Let's talk anti-roll bars

[Matt@BOS]

I've been testing and tuning my '69 Camaro with DSE underpinnings this year to get it to drive they way I want. I've played around with springs, sway bars and tires to try and get the car as neutral handling as possible. I try to only make one change at a time, but occasionally I will have to make two, i.e. if I'm replacing tires, sometimes I will change brands and throw on different springs as well.

Now, to what I wanted to discuss, is there a point where stiffening the rear of a car will decrease grip at the front, and/or increase grip at the rear?
Of the changes I've made, increasing rear sway bar stiffness seemed to increase the amount of understeer into transitional oversteer that I experienced. Additionally, I recently made a change to the front of the car. I increased spring rate and deccreased roll bar stiffness to try to get the car to have less brake dive with similar steady state cornering, but ended up with a car that seemed to put power down exceptionally well but exhibited more understeer, especially applying power with slight steering input. I'm curious, can limiting the amount of roll on the back of the car keep the outside front from loading up with weight, and "biting?"


Matt

[Ron Sutton]

Hey Matt,

so we all can have a better feel of what you're doing ... can you share all the details of your suspension ... tire brand & sizes, spring rates, anti-roll bar types & diameters, type of shocks, type of rear suspension (assuming it is a double A-arm front suspension) ... and front end geometry if you have it?

Plus ...
How heavy is the car?
Power output, trans & gear ratio?
What type of driving are you doing ... AutoX, road courses?

That will help get us all out of the dark to be able to engage in somewhat educated conversation.

[Rod]

yea!!! Matt :naughty: tell me all about your spring rates, anti-roll bar types & diameters, type of shocks, type of rear suspension....:smoke:...really I noticed the same thing I increased the rear bar on the car and stiffened the shocks and ended up with more traction

[Ron Sutton]

:hah: You're funny Rod.

I think I can tell you what's happening ... and why ... but I want to be sure of the set up ... so I don't stick my foot in my mouth. I wouldn't want to make assumptions & jump to the wrong conclusion.

You know what happens when you make assumptions ... right? You make an ass out the umptions. (Hmmm ... that didn't sound right). :evil:

[Matt@BOS]

Hey Ron, funny you should ask for details. I'd originally typed out a ton of details and then deleted them because I thought it might be better to talk from a broader conceptual level at first. I was hoping it might draw more people in, especially if they had personal experiences and questions of their own.

Here are the details:

1969 Camaro with 454 LS7 (gen IV), T56 Magnum, 3.73 gears, 18x9 and 18x11.5 wheels with 275/35 F, 315/30 R tires. DSE subframe and quadralink. 3500lbs with a full tank, sans driver. 51/49 F/R weight distribution. cross weights are pretty close. I think the biggest short coming of the car, which I am currently addressing is the narrower front than rear track width.

Anyway, I started the year with 450lb front springs and a .250" wall front bar with 250lb rear springs and DSE's 1-1/8" rear bar on the softest setting (of two settings). The car had pretty good bite and turn in, but it was wearing the outside tires badly and it was the tire was being overloaded because it would skip, or hop once before taking a set. The easiest adjustment I could make at the time was to adjust the rear bar and stiffen it up since pretty much any tuning guide says to soften the front or stiffen the rear to reduce understeer. Seeing as the front felt too soft I stiffened the rear, only to notice that I now had decent initial turn in with terrible mid corner push turning into transitional oversteer, making the car really loose putting power down.

Eventually I arrived at a set up I was reasonably happy with. 575lb springs/.250" bar front and 300lb/1-1/8" bar on the stiffest setting. I ended up changing though because the rear shocks I had were shot, so I put in working shocks (JRI) and replaced the springs with 275 to test. and I also wanted to give Falken tires a try. These changes gave me understeer that was most noticeable on turn in, but the functioning rear shocks greatly fixed traction issues as I used to start losing traction on auto crosses mid way through a straight since the rear springs wasn't being controlled.

In an effort to smooth turn in transitions I changed the front to a stiffer 700lb spring and softened the anti roll bar to .120" wall thickness with the hope being that it might solve the lack of turn in under braking. The car has always felt it never wanted to respond to trail braking, with the best turn in happening when the car was slowed and without your foot on the brake or gas.

I know there is probably no such thing as too much information, but there are a lot of different little things going on, and as I'm sure you know, fixing one thing always changes something else.

Matt

[Ron Sutton]

That is great information that helps me to have a little clearer picture. I still need a "few" more details.

When you talk about your front sway bar, you mention wall thickness but not diameter. Please post the diameter ... and effective bar rate ... if you know it.

In the rear, you mention having the 1-1/8" sway bar on the stiffest setting. Please post the effective bar rate for it too ... if you know it.

Are you on a coil-over setup or separate shocks & springs ?

Did you put JRI shocks on all 4 corners ... or just the rear?

Lastly, are your results coming from driving in Autox or big road courses?


Thanks, Ron Sutton

[Rod]

Matty, I think were both using the hyperco springs I ended up with 200 lb rears and 700 fronts, but hell you know that works I could change next week, I think that some of the lack of trail braking is also tire offsets, I noticed that scenario at Del Mar with the 10" rim on all for corners I had 0(zero) trail brake I switched to the smaller 8" inch 255 front wheel set up front and the turn in was quicker mid way in the turn allowing the rear to come around, instead of pushing through the corners

[Matt@BOS]

Rod, we are both using Hyperco springs, although I have a stray set of AFCO ones that Cris let me borrow to test (300lb) and a few sets of DSE branded ones on the shelf.

Ron, here is a chart from Speedway showing the bar rates. You will want to look at the 1-1/4" OD listings. Forgive me though, because I don't know what the length of the arm is. I think it is either 10" or 12."

The rear rates are:
Front Hole: 344 lb/in. Rear Hole: 402 lb/in.

Matt

[Ron Sutton]

Matt,

Did you put JRI shocks on all 4 corners ... or just the rear?

[Ron Sutton]

Matt,

Did you put JRI shocks on all 4 corners ... or just the rear?

[Ron Sutton]

For clarity sake, Matt … please read this and make sure I am interpreting your writings correctly. If not, copy, paste & edit into the next post.

----------------------------------------------------------------------------------------------

Your car is a 1969 Camaro with 454 LS7 (gen IV), T56 Magnum, 3.73 gears, 18x9 and 18x11.5 wheels with 275/35 F, 315/30 R tires. DSE subframe and quadralink. 3500lbs with a full tank, sans driver. 51/49 F/R weight distribution, with “close” cross weights” & narrower front than rear track width.

You have had basic 5 suspension set-ups:

#1
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 344#
Notes: The car had pretty good bite and turn in, but it was wearing the outside tires badly and it was the tire was being overloaded because it would skip, or hop once before taking a set.

#2
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 402#
Notes: I stiffened the rear, only to notice that I now had decent initial turn in with terrible mid corner push turning into transitional oversteer, making the car really loose putting power down.

#3
Front Springs: 575#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 402#
Notes: I arrived at a set up I was reasonably happy with.

#4
Front Springs: 575#
Front Sway Bar: 447#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes gave me understeer that was most noticeable on turn in, but the functioning rear shocks greatly fixed traction issues as I used to start losing traction on auto crosses mid way through a straight since the rear springs wasn't being controlled.

#5
Front Springs: 700#
Front Sway Bar: 295#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes seemed to increase the amount of understeer into transitional oversteer that I experienced & ended up with a car that seemed to put power down exceptionally well but exhibited more understeer, especially applying power with slight steering input.


Do I have this correct ?


Ron Sutton

[Rod]

thread HI-JACK! hey Ron that logo is familiar, I meet you at Pleasanton didn't I? you should have went for a ride along, OK back to your regularly scheduled program

[Ron Sutton]

Yes, Rod. I stopped by & looked at your baby while I was at the last Pleasanton GG event. Checking to see if you were running same size tires on all 4 corners.

Sorry I didn't introduce myself. I was visiting Brianne & Mike Maier most of the day.

[Rod]

I'm liking this!! now were talking real, fun, stuff,



For clarity sake, Matt … please read this and make sure I am interpreting your writings correctly. If not, copy, paste & edit into the next post.

----------------------------------------------------------------------------------------------

Your car is a 1969 Camaro with 454 LS7 (gen IV), T56 Magnum, 3.73 gears, 18x9 and 18x11.5 wheels with 275/35 F, 315/30 R tires. DSE subframe and quadralink. 3500lbs with a full tank, sans driver. 51/49 F/R weight distribution, with “close” cross weights” & narrower front than rear track width.

You have had basic 5 suspension set-ups:

#1
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 344#
Notes: The car had pretty good bite and turn in, but it was wearing the outside tires badly and it was the tire was being overloaded because it would skip, or hop once before taking a set.

#2
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 402#
Notes: I stiffened the rear, only to notice that I now had decent initial turn in with terrible mid corner push turning into transitional oversteer, making the car really loose putting power down.

#3
Front Springs: 575#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 402#
Notes: I arrived at a set up I was reasonably happy with.

#4
Front Springs: 575#
Front Sway Bar: 447#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes gave me understeer that was most noticeable on turn in, but the functioning rear shocks greatly fixed traction issues as I used to start losing traction on auto crosses mid way through a straight since the rear springs wasn't being controlled.

#5
Front Springs: 700#
Front Sway Bar: 295#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes seemed to increase the amount of understeer into transitional oversteer that I experienced & ended up with a car that seemed to put power down exceptionally well but exhibited more understeer, especially applying power with slight steering input.


Do I have this correct ?


Ron Sutton

[Tomswheels]

Matt, your suspension sounds like its working to eliminate too much roll, which is backwards. You want to ENCOURAGE roll, I included pics to show how it SHOULD look:

https://static1.pt-content.com/images/pt/2013/06/cuuuda1_zps9f2ab644-1.jpg (http://s1357.photobucket.com/user/tomswheels/media/Barracuda/cuuuda1_zps9f2ab644.jpg.html)

See how the front wheels appear to be pointed AWAY from the Apex, thats a great sign things are going well.

https://static1.pt-content.com/images/pt/2013/06/cuuuda2_zpscf3442c6-1.jpg (http://s1357.photobucket.com/user/tomswheels/media/Barracuda/cuuuda2_zpscf3442c6.jpg.html)

In this one we see the benefits of a 230(+) pound "driver"... Im getting the most grip possible from the outside edge of the left side tires.

[Tomswheels]

https://static1.pt-content.com/images/pt/2013/06/cuuuda5_zps5b8b108b-1.jpg (http://s1357.photobucket.com/user/tomswheels/media/Barracuda/cuuuda5_zps5b8b108b.jpg.html)

No comment needed, however, note the front left wheel / rear bumper angle. Almost perfect! :thankyou:

[Matt@BOS]

For clarity sake, Matt … please read this and make sure I am interpreting your writings correctly. If not, copy, paste & edit into the next post.

----------------------------------------------------------------------------------------------

Your car is a 1969 Camaro with 454 LS7 (gen IV), T56 Magnum, 3.73 gears, 18x9 and 18x11.5 wheels with 275/35 F, 315/30 R tires. DSE subframe and quadralink. 3500lbs with a full tank, sans driver. 51/49 F/R weight distribution, with “close” cross weights” & narrower front than rear track width.

You have had basic 5 suspension set-ups:

#1
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 344#
Notes: The car had pretty good bite and turn in, but it was wearing the outside tires badly and it was the tire was being overloaded because it would skip, or hop once before taking a set.

#2
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 402#
Notes: I stiffened the rear, only to notice that I now had decent initial turn in with terrible mid corner push turning into transitional oversteer, making the car really loose putting power down.

#3
Front Springs: 575#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 402#
Notes: I arrived at a set up I was reasonably happy with.

#4
Front Springs: 575#
Front Sway Bar: 447#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes gave me understeer that was most noticeable on turn in, but the functioning rear shocks greatly fixed traction issues as I used to start losing traction on auto crosses mid way through a straight since the rear springs wasn't being controlled.

#5
Front Springs: 700#
Front Sway Bar: 295#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes seemed to increase the amount of understeer into transitional oversteer that I experienced & ended up with a car that seemed to put power down exceptionally well but exhibited more understeer, especially applying power with slight steering input.


Do I have this correct ?


Ron Sutton

Ron, that is 99 percent correct
On setup #4 I changed rear springs from 300lb to 275lb. JJ at JRI and I discussed between the 250-325lb rates I had on the shelf and put the 275lb springs on as a starting point since I was also swapping in rear shocks that had nitrogen, and well... functioned.

Oh, and before I forget, I do have JRI shocks on all four corners. They have low speed rebound adjustment, and a high speed damping adjuster. I can also add or drop pressure.

Thanks for your interest in sorting things out

Matt

[Matt@BOS]

Tom, I saw your Barracuda tearing up the Good Guys peanut course, and when I went for a ride I was afraid of capsizing. Perhaps that fear caused me to overcompensate by limiting weight transfer too much on my car.

Matt

[Tomswheels]

Understood Matt, im sure Ron will have a more intelligent observation, but have you ever tried a fairly stiff front setup with little (or even no) rear sway bar? This has worked with my (admttedly not as well balanced) cars in the past...

[Ron Sutton]

Ron, that is 99 percent correct
On setup #4 I changed rear springs from 300lb to 275lb. JJ at JRI and I discussed between the 250-325lb rates I had on the shelf and put the 275lb springs on as a starting point since I was also swapping in rear shocks that had nitrogen, and well... functioned.

Oh, and before I forget, I do have JRI shocks on all four corners. They have low speed rebound adjustment, and a high speed damping adjuster. I can also add or drop pressure.

Thanks for your interest in sorting things out

Matt

In which stages (1-5) did you have the 300# rear springs on ?

All JRI shocks come with a dyno sheet. Can you scan & post them please? We won't start with shock tuning, but we will finish there, as that is what shocks allow you to do ... fine tune & dial in a good spring & Anti-Roll Bar package.

[Ron Sutton]

Before we get into problems & solutions on your specific application … I want to share with you a viewpoint I use to make tuning easier … then outline terms & critical tuning concepts … so we’re on the same page.

We all know competition cars are COMPLEX. There are literally over 200 AREAS of things to TUNE in the suspension alone. I find what helps a Tuner/Crew Chief to become more confident is ... knowledge (of course) ... experience (of course) ... knowing what a mechanical change actually effects on track … and how each tuning change of affects other areas.

But also, as a Tuner/Crew Chief, having a viewpoint that makes all this complexity ... simpler to understand … provides clarity & builds confidence.

I have been fortunate to develop many crew chiefs over the years to work with me on my race teams. Teaching them everything they need to master is a long term commitment on my part & theirs. It takes years. But simplifying things help them grasp concepts quicker ... and develops confidence in their tuning decisions.

Let's simplify things first. Remember this little corny phrase: 4x4x2+2

It is short (like an acronym, but using numbers) for ALL the things that competition car Designers, Tuners & Crew Chiefs deal with. There are 4 key areas with 4 major ingredients, operating in 2 worlds … plus 2 wild cards. 4x4x2+2 is just a simple way to remind us what we're dealing with.

The 4 key areas are: power, braking, handling & aerodynamics (in no particular order.) Obviously these all play a role in the performance of the car … and in many cases affect each other.

Each Key area has 4 major ingredients that define it & of course affect it.

For power, the 4 major ingredients are:
Airflow
Fuel management
Spark control
Structure Design

For braking, the 4 major ingredients are:
Hydraulics
Leverage
CoF
Structure Design

For handling, the 4 major ingredients are:
Tires
Weight transfer … to and from tires
Geometry affecting … the tires
Structure Design

For aerodynamics, the 4 major ingredients are:
Force
Drag
Turbulence
Structure Design

When I said competition cars operate in two worlds, what I really mean is we do a lot of design, set up & tuning to the car in a “static state” … then go drive it HARD … and everything is affected & different when the car is in a "dynamic state" on track.

No pun intended, but the 2 wild cards are the track & the driver. The track environment is constantly changing, and good Tuners/Crew Chiefs tune to the changing conditions.

As long as we use human drivers, this will be a variable. Some drivers are more consistent & some less, but none of them are robots, so there will be inconsistencies. Some drivers are learning & improving, some not & even some declining in their abilities, but again, they are not static. Some drivers are more of a wild card than others.


I find, as long as we embrace these 4 key areas, understand the 4 major ingredients that define & affect them, remember the car is acting in a dynamic state on track & account for the 2 wild cards … the job of Tuner/Crew Chief gets more clear, less daunting and making tuning decisions becomes easier, quicker & more confidently.


----------------------------------------------------------------------------------------------

Let’s get on the same page with terms & critical tuning concepts.

Shorthand & Acronyms
IF = Inside Front Tire
IR = Inside Rear Tire
OF = Outside Front Tire
OR = Outside Rear Tire
*Inside means the tire on the inside of the corner, regardless of corner direction.
Outside is the tire on the outside of the corner.

ARB = Anti-Roll Bar
FRC = Front Roll Couple
RRC = Rear Roll Couple
TRS = Total Roll Stiffness
TAR = is those black round things the car rolls on. (Sorry, couldn’t resist)
WT = Weight Transfer

CG = Center of Gravity
RC = Roll Center
IC = Instant Center
RA = Roll Angle

----------------------------------------------------------------------------------------------

TERMS:

Total Roll Stiffness: is the mathematical calculation of the “roll resistance” built into the car with springs, ARB’s & their geometry. Stiffer springs & bigger ARB’s make this number go UP & the roll angle of the car to be less.

Roll Couple … front to rear … is expressing the roll stiffness separately & often in %. If we say the Front has 58% roll couple (then the rear automatically has 42%) … so the front suspension of the car is resisting roll more than the rear.

Roll Angle: is the amount the car “rolls” over from side-to-side in cornering, usually expressed in degrees.

Spring rate = pounds of linear force to compress the spring 1”.
Spring force = total amount of force (weight and/or weight transfer) on the spring.

Anti-Roll Bar, ARB, Sway Bar & Anti-Sway Bar … all mean the same thing. Kind of like “slim chance” & “fat chance” ... :)
ARB Rate = Pounds of torsional force to twist the ARB 5 degrees. (This has been corrected.)

Dive = is the front suspension compressing under braking & cornering forces.
Rise = can refer to either end of the car rising up.
Squat = refers to the car planting the rear end on launch or under acceleration
Roll = Side to side body rotation … aka body roll.
Pitch = Fore & aft body rotation. As when the front end dives & back end rises under braking or when the front end rises & the back end squats under acceleration.

Grip & Bite = are my slang terms for tire traction.


Track width = is center to center of the tread.
Tread width = is outside to outside of the tread.
A lot of people get those confused & our conversations get sidelined.
* The definitions for these 2 were swapped & has now been corrected

Rate = The rating of a device often expressed in pounds vs distance. A 450# spring takes 900# to compress 2”.
Rate = The speed at which something happens, often expressed in time vs distance. 3” per second. 85 mph.
* Yup, dual meanings.

----------------------------------------------------------------------------------------------

ASSUMPTIONS:

Let’s assume we’re not changing any ride heights, unless discussed. In race cars & many (but obviously not all) PT cars, the spring height is adjustable & if we make a spring rate change, we are putting the car back to the EXACT same ride heights, unless it is desired & discussed to change ride heights.

----------------------------------------------------------------------------------------------

20 CRITICAL TUNING CONCEPTS:

1. What you do WITH & TO the TIRES ... are the key to performance. Contact patch is the highest priority.

2. Geometry design, settings & changes should be to improve how the tires contact the road dynamically.

3. The design structure of every component affects how well that component handles forces inflicted upon it.

4. After the car is built, tires are selected & the geometry is optimum … most chassis tuning is to control the degree of weight transfer to achieve the traction goal.

5. Force (weight & weight transfer) applied to a tire adds grip to that tire. With the exception of aerodynamics, weight transfer from tire(s) to tire(s) is the primary force we have to work with.

6. Anti-Roll Bars primarily control how far the front or rear suspension (and therefore chassis) “rolls” under force, and only secondarily influences the rate of roll. Stiffer bars reduce roll angle, engaging the inside tires more.

7. Springs primarily control how far a suspension corner travels under force, and only secondarily influences the rate of travel. Shocks primarily control the rate of suspension corner travel under force, and only secondarily have influence on how far.

8. Springs, Shocks & Anti-Roll Bars need to work together “as a team” … with the springs’ primary role of controlling dive & rise, Anti-Roll Bars’ primary role of controlling roll & Shocks primarily role controlling the rate of both. They all affect each other, but if we choose the right tool for the job, we create a harmonious team.

9. I find in production based cars, we can go no faster through a corner than the front tires can grip. Balancing the rear tire grip to the front … for balanced neutral handling … is relatively easy … compared to the complexities of optimizing front tire grip.

10. The front tires need force, from weight transfer on corner entry, to provide front tire GRIP. Too little & the car pushes … too much & the car is loose on entry. The rear tires need force, from weight transfer on corner exit, to provide rear tire GRIP. Too little & the car is loose … too much & the car pushes on exit.

11. Tuning to allow a suspension corner … to compress quicker or farther … provides more force & therefore more grip to that tire … up to the limits of the tire. Tuning to allow a suspension corner … to extend/rebound quicker or farther … provides more force & therefore more grip to the opposite corner’s tire … up to the limits of the tire.

12. Softer springs allow more compression travel & therefore more force onto the tire … for MORE GRIP on that tire ... and less grip on the opposite tire. Stiffer springs reduce compression travel & therefore lessen force onto the tire … for LESS GRIP on that tire ... retaining more grip on the opposite tire.

13. Optimum roll angle works & loads both sides of the car’s tires “closer to even” ... within the optimum tire heat range … providing a consistent "long run set-up" & optimum cornering traction throughout a multi-lap event. Long run set-ups typically take ½ a lap to a whole lap for the tires to “come in” 100%.

14. Higher roll angles work better in tight corners but suffer in high speed corners. Lower roll angles work better in high speed corners but suffer in tight corners. The goal on a road course with various tight & high speed corners … is to find the best balance & compromise that produces the quickest lap times.

15. Too much roll angle overworks the outside tires in corners & underworks the inside tires. Too little roll angle underworks the outside tires in a corner. Excessive roll angle works the outside tires too much … may provide an “ok” short run set-up … but will be “knife edgy” to drive on long runs. The tire heat up quicker & go away quicker. If it has way too much roll angle … the car loses grip as the inside tires are not being utilized.

16. Too little roll angle produces less than optimum grip. The car feels “skatey” to drive … like it’s “on top of the track.” The outside tires are not getting enough load from force, therefore not gripping enough. Tires heat up slower & car gets better very slowly over a long run as tires gain heat.

17. I learned early that tuning is NOT linear 2 directions with stops at the ends. A car can be loose because it has too little roll angle in the rear & is not properly loading the outside rear tire ... or loose because it has too much roll angle in the rear & is not properly loading the inside rear tire. A car can be pushy because it has too little roll angle in the front & is not properly loading the outside front tire ... or pushy because it has too much roll angle in the front & is not properly loading the inside front tire.

18. The car’s Center of Gravity acts as a lever on the Roll Center … separately front & rear. Higher CG’s and/or lower RC’s increases roll angle. Lower CG’s and/or higher RC’s decrease roll angle. Getting the front & rear of the car to roll similar is desired. Getting them to roll exactly the same is not, because …

19. Goal: To have optimum grip on all tires and disengage the inside rear tire (to a degree) to turn well … then re-engage the inside rear tire (to a higher degree) for maximum forward bite on exit. So, on entry & mid-corner, the car needs to roll less in the front to keep both front tires engaged for optimum front end grip, while allowing the car to roll slightly more in the rear to disengage the inside rear tire, to a small degree, to turn better. For optimal exit, the car will have more roll in the front & less in the rear to re-engage the inside rear tire to a higher degree than it was on entry & exit, for maximum forward bite (traction) on exit.

20. Don’t forget the role & affects the engine, gears, brakes, driver & track conditions each have on handling.


----------------------------------------------------------------------------------------------

After you have read this ... and have time to digest it ... the cause of your handling challenges may become more clear. Regardless, I'll be back tomorrow with what i think is an explanation for your particular issues.



If anyone has any questions, feel free to chime in on this thread.

Ron Sutton

[Tomswheels]

:hammer:

[Ron.in.SoCal]

"TAR = is those black round things the car rolls on. (Sorry, couldn’t resist)"

That's a NASCAR term right? As in, "Last pitstop he took two TARs!" :lol:

Ron such a pleasure to watch you in action. Keep going Sir! :cheers:

[Ron Sutton]

"TAR = is those black round things the car rolls on. (Sorry, couldn’t resist)"

That's a NASCAR term right? As in, "Last pitstop he took two TARs!" :lol:

Ron such a pleasure to watch you in action. Keep going Sir! :cheers:

No, Ron ... that's a drag racing term I picked up in the South. After the race was over ... talking with racer buddies over several adult beverages ... a friend said he was having problems with tar. I said, we used to also. But now we put WD-40 on the fenderwells before runs, and the tar doesn't stick. He looked at me like I was drunk ... no comment ... and said, "No Ron. I having problems getting my tars to hook up."

Oh. :doh:

[Ron Sutton]

Tom,

Tom ....


Tom ... you going to be ok? :seizure:

[Tomswheels]

Awesome stuff. Trying to figure out how to get my Torsion bars and leaf springs to understand it all...

[Matt@BOS]

Ron, hopefully this isn't too confusing, but in place of setup 2, I actually had two setups with minor differences which mostly drove the same.

setup 3:
Front Springs: 550#
Front Sway Bar: 447#
Rear Springs: 300#
Rear Sway Bar: 402#
Notes: I arrived at a set up I was reasonably happy with. last setup with AFCO shocks on all corners

setup 3.5
Front Springs: 575# (Now with JRI shocks up front)
Front Sway Bar: 447#
Rear Springs: 300#
Rear Sway Bar: 402#
Notes: I arrived at a set up I was reasonably happy with. I ran the same little track at Adams Motorsports track in Riverside (autocross sized) before and after making the changes, and found the JRIs to be slightly quicker. I have driven the track many times, and I was a bit quicker with the JRIs. Perhaps it was just confidence but I felt like the JRIs functioned better through quick transitions and gave better turn in feel. I had to back compression off of the AFCOs to get them to respond the way I wanted them to in 180 degree slow speed, tight corners, which left me with a car that felt a little numb and was slightly slower to react in slalom situations, but otherwise worked well. It is probably pointless rambling about that since I've changed out the shocks, and we don't know have dyno sheets of the afcos, but more information never hurt, right?

I will have to go look for the shock dyno charts on the JRIs, if I don't have them I can always call DSE.

Matt

[Ron Sutton]

Thanks for the update Matt. I'll create an updated sheet, so as we discuss how changes affect the car ... you & I can refer back to actual setups you had.

I'm hoping Rod & Tom join in the conversation as well, with their experiences.

[Ron Sutton]

Awesome stuff. Trying to figure out how to get my Torsion bars and leaf springs to understand it all...

Ain't no big thing. A spring is a spring, regardless of how man shaped it. If you think of it this way, it all makes sense.

A. We are always working to get the 4 tires to optimize contact patch.
B. There is a roll angle the car is happy at for each corner ... and a best compromise for the various corners of a track.

Have you added a track bar to your leaf springs?

[Ron Sutton]

For clarity sake, Matt … please read this and make sure I am interpreting your writings correctly. If not, copy, paste & edit into the next post.

----------------------------------------------------------------------------------------------

Your car is a 1969 Camaro with 454 LS7 (gen IV), T56 Magnum, 3.73 gears, 18x9 and 18x11.5 wheels with 275/35 F, 315/30 R tires. DSE subframe and quadralink. 3500lbs with a full tank, sans driver. 51/49 F/R weight distribution, with “close” cross weights” & narrower front than rear track width.

You have had basic 5 suspension set-ups:

#1
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 344#
Notes: The car had pretty good bite and turn in, but it was wearing the outside tires badly and it was the tire was being overloaded because it would skip, or hop once before taking a set.

#2
Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 402#
Notes: I stiffened the rear, only to notice that I now had decent initial turn in with terrible mid corner push turning into transitional oversteer, making the car really loose putting power down.

#3
Front Springs: 550#
Front Sway Bar: 447#
Rear Springs: 300#
Rear Sway Bar: 402#
Notes: I arrived at a set up I was reasonably happy with. last setup with AFCO shocks on all corners

#3.5:
Front Springs: 575# (Now with JRI shocks up front)
Front Sway Bar: 447#
Rear Springs: 300#
Rear Sway Bar: 402#
Notes: I arrived at a set up I was reasonably happy with. I ran the same little track at Adams Motorsports track in Riverside (autocross sized) before and after making the changes, and found the JRIs to be slightly quicker. I have driven the track many times, and I was a bit quicker with the JRIs. Perhaps it was just confidence but I felt like the JRIs functioned better through quick transitions and gave better turn in feel. I had to back compression off of the AFCOs to get them to respond the way I wanted them to in 180 degree slow speed, tight corners, which left me with a car that felt a little numb and was slightly slower to react in slalom situations, but otherwise worked well. It is probably pointless rambling about that since I've changed out the shocks, and we don't know have dyno sheets of the afcos, but more information never hurt, right?

#4
Front Springs: 575#
Front Sway Bar: 447#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes gave me understeer that was most noticeable on turn in, but the functioning rear shocks greatly fixed traction issues as I used to start losing traction on auto crosses mid way through a straight since the rear springs wasn't being controlled.

#5
Front Springs: 700#
Front Sway Bar: 295#
Rear Springs: 275#
Rear Sway Bar: 402#
Additional Changes: Put JRI Shocks on the rear & Falken Tires all the way around
Notes: These changes seemed to increase the amount of understeer into transitional oversteer that I experienced & ended up with a car that seemed to put power down exceptionally well but exhibited more understeer, especially applying power with slight steering input.


Do I have this correct ?


Ron Sutton

[Matt@BOS]

I mentioned earlier that I was widening the front track width, but never got into specifics. It is a pretty big change. I just picked up a set of widened Fiberglass fenders which should allow me to move the wheels out 1.5" per side from what I have now. It should allow me to run a roughly 71"/70" front to rear track. My car is out getting getting the rear center section fixed after all of the ring gear bolts fell out, for a second time. So, I can't measure for sure, but the other Camaros in the shop allowed me to work backwards to those numbers, and I kind of cringed when I figured out what they probably are.

So, let me pose one more question for you, and hopefully we aren't getting ahead of ourselves too much, but this relates back to one of Rod's questions. Can we get into undersquare versus square front to rear tire widths, and how they affect turn in?

[Matt@BOS]

Oh, and yes, the latest sheet of setups is correct and includes all of the combinations I've I ran on autocrosses. I did go out to Big Willow, and have a few notes on that setup but for the sake of focus, I haven't included those notes.

[Ron Sutton]

Matt,

When you say "71"/70" front to rear" ... that's not track width, that's tread width ... or you really have a WIDE car. :seizure:

Small difference in measuring ... big difference in how it affects the car. If your tires were the same width ... even though the measurements are outside-to-outside & need to be center-to-center ... the ratio of 1" wider in front would be fine.

If you make your car have a "tread width" of 71" front & 70" rear ... with your 275/35 Front tires on 18x9 wheels, which have around 9.8" tread on the ground and your 315/30 Rear tires on 18x11.5 wheels have about 11.8" of tread on the ground ... that would make the front track width 61.2" ... and your rear track width 58.2" .... 3" wider in the front .... hmmmmmm ... wrong direction ... will make the car push like a dump truck ... not good. Let's discuss this along with everything else.

To discuss how the car has been handling ... we need to clarify the track width the car has now.

Next steps ....

1. Measure center of tread to center of tread ... front & back ... and post the #'s.
* (or outside of tread on one & inside of tread on the other)

2. Provide me with accurate tire tread width numbers for future calculations.



If anyone has any questions, feel free to chime in on this thread.

Ron Sutton

[Ron Sutton]

Can we get into undersquare versus square front to rear tire widths, and how they affect turn in?

Any time you widen the front track width ... and leave the rear track width the same ... You are tightening the car on Corner Entry & Exit ... meaning you're adding more rear tire grip. If the car was pushing already .. the push will get worse. The same would be true if you left the front track width alone and narrowed the rear track width.

The handling in the center of the corner ... also known as the "roll through zone", where you're off the brake & haven't picked up the throttle yet ... can have different results. If the car had too much Roll Angle ... the wider front track width may help reduce the roll angle & load the IF tire more, adding grip to the front end of the car, helping it to turn better.

On the other hand, if the car already had the correct Roll Angle or too little Roll Angle ... and the IF tire was already loaded & doing it's job ... the wider front track width will reduce the roll angle even more & unfortunately may load the IR tire to a higher degree (bad) adding grip to the rear end of the car ... contributing to a tight or push condition.

Read my long winded "book" in post #21 ... then read this again ... and let your mind digest it some. Let me know when you're ready to pick up the conversation again, and if you had any "Ah Ha" moments.


If anyone has any questions, feel free to chime in on this thread.

Ron Sutton

[Matt@BOS]

Hey Ron, here is what you wrote:

Track width = is outside to outside of the tread.
Tread width = is center to center of the tread.

It sounds like you meant to write the opposite, no?

So, let me take another stab at this,
overall width is currently 68"/70"
That would make the tread width closer to 67"/69"
and the track width would then be 57.2" front and 57.2" rear

With the widened front fenders I was planning on adding more front tire, so instead of a 9" wheel I would be moving up to a 10.5" or possibly 11" wheel. This would allow me to run a 295 or 315 front tire, depending on brands. Falken only makes a 295/40, which is too tall, so I would be looking to run their 315/30/18s all the way around.

I believe this would change things to:
58.2" front, 57.2" rear track width.

Again these numbers are approximate because the car isn't in front of me, but if it is fine with you, let's run with these numbers. I can always work backwards and plug in the actual numbers later, right?

[Ron Sutton]

Hey Ron, here is what you wrote:

Track width = is outside to outside of the tread.
Tread width = is center to center of the tread.

It sounds like you meant to write the opposite, no?
Hmm. I went back & looked to fix it & can't find the error. I found the error in post #21 & corrected it. Thanks for catching it.

Regardless, Track width is center to center of the tread ... and Tread width is outside to outside of the tread.


So, let me take another stab at this,
overall width is currently 68"/70"
That would make the tread width closer to 67"/69"
and the track width would then be 57.2" front and 57.2" rear
You're on the right track. My math says 56.6" front & 57.0" rear.

I'm using these #'s which are "in the ballpark" ...
275/35 Front tires on 18x9 wheels should work out to 10.6" overall & 9.8" tread on the ground
315/30 Rear tires on 18x11.5 wheels should work out to 12.4" overall & 11.8" of tread on the ground
* Again, when you get your car back, measure everything "for real" & we'll work from those #s.




With the widened front fenders I was planning on adding more front tire, so instead of a 9" wheel I would be moving up to a 10.5" or possibly 11" wheel. This would allow me to run a 295 or 315 front tire, depending on brands. Falken only makes a 295/40, which is too tall, so I would be looking to run their 315/30/18s all the way around.
OMG ... this would be a great move ... because 1 of the issues your current set-up has is the small fronts & big rears.

But if the front track width goes past 58.0" ... or 1" more than the rear ... you may compound your tuning challenges.

Assuming you're going from a 9" wheel to an 11" wheel, the back spacing will need to be .3" MORE than your current front wheels. That would place .3" of the additional 2.0" of tire width on the inside, closer to the frame & 1.7" of the additional 2.0" of tire width on the outside, closer to the fender. My suggestion is this is the MAX I would push the tires & wheels out. This creates a 58.0" track width

I feel optimum would be back spacing .5" MORE than your current front wheels. That would place .5" of the additional 2.0" of tire width is on the inside closer to the frame & 1.5" of the additional 2.0" of tire width is on the outside closer to the fender. This creates a 57.6" track width ... .6 or 6/10 of an inch wider than the rear. :naughty:



I believe this would change things to:
58.2" front, 57.2" rear track width.

Again these numbers are approximate because the car isn't in front of me, but if it is fine with you, let's run with these numbers. I can always work backwards and plug in the actual numbers later, right?

Yes, let's run with these numbers & the concept ... and work out actual numbers when you have your car back.

[Matt@BOS]

Well, I can't go inboard with the front wheels anymore without seriously limiting steering, but I can go out .25 inches per side in the rear if that would help.

[Ron Sutton]

Well, I can't go inboard with the front wheels anymore without seriously limiting steering, but I can go out .25 inches per side in the rear if that would help.

Awesome. That should make the front track width 58.6" and the rear track width 57.5" ... give or take until you measure your car for real.

2 questions ...

1. Have you read Post #21 thoroughly yet?
2. If so, are you getting ideas of why your car is pushing with bigger rear sway bars?


Ron Sutton

[QuarterD25]

Mind blowen....

[Ron Sutton]

Mind blowen....

Sorry ...

[Rod]

ha ha ha ha :smashcomp ha ha ha ha


Mind blowen....

it will get better! close your eyes young Jedi and visualize

[Greg from Aus]

Thanks so much Ron, for sharing you knowledge with us. When my car is finally finished, I would love the opportunity to pick your brains for an initial set up.



Regards
Greg

[Ron Sutton]

Thanks so much Ron, for sharing you knowledge with us. When my car is finally finished, I would love the opportunity to pick your brains for an initial set up.



Regards
Greg

I'd be happy & honored to help Greg. Feel free to chime in on the technical posts I'm involved in.

Ron Sutton

[QuarterD25]

So maybe a bit of a tangent but how do you tell if you have too much negative camber or is there too much? Also, how do you determine how much camber you need in a turn?

[Matt@BOS]

Hey Ron, I finished going over my "homework." Did you make sure to put the information I was looking for at the bottom so I would have to read over everything? :lol:

The photos capturing my car running at events correspond well with the info you gave. The car tends to dive under braking, while loading up weight on the outside front tire in the turn, yet as I roll into and through corners, it doesn't look like I get much rear roll. You mentioned that the goal of setting up a rear suspension was to get it to be able to unload weight from the inside rear tire on entry and be able to load the inside rear tire on exit. Does this mean if the rear has insufficient roll, the inside rear tire will be too planted and will be one of the factors leading to the understeer because the contact patch created by both rear tires is too great relative to the front?

Thanks for the help,

Matt

[Ron Sutton]

So maybe a bit of a tangent but how do you tell if you have too much negative camber or is there too much? Also, how do you determine how much camber you need in a turn?

No worries. I'm glad you chimed in.

Sure, you can have too much of anything in cars, be it camber, caster, toe, camber gain ... camshaft, carb, cylinder port size, compression, header size, fuel, timing, etc. I'm sure you have seen this in many areas. It's never a simple answer, or one specific number, that works for every situation. The correct answer for every one of those things listed is, "it depends on the combination".

That's not a cop out. Competition cars are COMPLEX. There are literally over 200 AREAS of things to TUNE in the suspension alone. What helps a Racer/Tuner/Crew Chief to become more confident is ... knowledge (of course) ... experience (of course) ... knowing what a mechanical change actually effects on track … and how each tuning change of affects other areas.

Every one of these items I listed above will have effects on other areas, so as a race car Designer & Crew Chief, I can't look at Camber as an individual thing. I have to look at the spindle KPI/SAI, Caster, Caster Gain/Loss, Camber, Camber Gain/Loss as a team ... a team of geometry devices that I need to work together to improve how the tires contact the road dynamically.

Having done this for years, designing, building & racing a lot of cars, in a wide variety of racing, has given me some insight into how things work. So now it's a little easier & quicker for me to "get there" to the sweet spot. I have a process I like to use ...

A. I have to work out the Spindle KPI/SAI with the length of the A-arms, tire width & wheel backspacing ... to end up with a desirable scrub radius.
B. Once I know the spindle KPI/SAI, that guides me on how much caster I need to build in to achieve a KPI/Caster Split favoring the caster.
C. I need to work out if we want caster gain, or for the caster to stay the same, as the front suspension compresses fully under braking & turning (called "Dive")
D. If I can get the caster I want ... statically and/or with gain ... so the KPI/Caster Split favors the caster ... I can run modest Camber, instead of aggressive camber, which is the goal. We're always going to run some static camber (negative). But if I can not get the KPI/Caster Split favoring the caster, I will need to more more aggressive with camber.
E. Once I know how much total camber I need for that combo, I work out how much of it is going to be static camber & how much is going to be camber gain.
F. How we get the camber gain, & how much ... is a function of the double A-arm geometry ... and therefore determines the car's static & dynamic roll center ... so they have to work as a team too.

All of this is to optimize both front tire's contact patch with the asphalt in the car's dynamic states when it's driven HARD ... meaning turning, braking, rolling, unwinding & accelerating to the limits of the car, tires & driver ... sometimes beyond. .

Of course there is no “perfect handling car” when driven at its limits. That’s why they’re called “limits” ... and why this is so challenging. The top Crew Chiefs & Tuners … that dial in the best balance, fastest compromise & win races … are highly sought after & well compensated.

The same applies to the rest of the car too ... meaning components & settings must work together as a team .. to achieve optimum performance. Engines need the short block geometry, heads, intake, carb, headers, cam, valvetrain, ignition, etc to all harmonize for optimum power & drivability. Springs, Shocks & Anti-Roll Bars need to work together as a harmonious team .. and that team must work with the car's front & rear geometry ... to optimize handling.

So ... your 2nd question was, "how do you determine how much camber you need in a turn?"

The real, no BS, answer is ... I need as much as it takes, but no more ... to work with my spindle KPI/SAI & caster ... to create a flat contact patch on the pavement ... "dynamically" ... which means the driver drove the car into the corner deep, braked hard, turned into & through the corner, let a roll a bit & rise, then rolled the throttle on as quickly as the tires would allow.

I know that was a complex answer, but I didn't want to simply throw you a BS #.



If anyone has any questions, feel free to chime in on this thread.

Ron Sutton

[Ron Sutton]

Hey Ron, I finished going over my "homework." Did you make sure to put the information I was looking for at the bottom so I would have to read over everything? :lol:
Of Course !!! :woot:

The photos capturing my car running at events correspond well with the info you gave. The car tends to dive under braking, while loading up weight on the outside front tire in the turn, yet as I roll into and through corners, it doesn't look like I get much rear roll. You mentioned that the goal of setting up a rear suspension was to get it to be able to unload weight from the inside rear tire on entry and be able to load the inside rear tire on exit. Does this mean if the rear has insufficient roll, the inside rear tire will be too planted and will be one of the factors leading to the understeer because the contact patch created by both rear tires is too great relative to the front?

Thanks for the help,

Matt

I say old chap ... you nailed it. That is the problem ... now. I'll make a series of posts to outline CEPS ... Causes, Effects, Problems & Solutions ... that address your original set-up & the tuning changes you made.

Please don't take offense as I outline some tuning mistakes I see. I just want to help, and it's just as important to learn from what didn't work ... as it is to learn from what did work. Sometimes it is a better lesson I find, because I won't forget it.

[Ron Sutton]

Matt,

In my opinion, the causes of your car’s handling became clear when you described how it was handling & what you tried.

I think you have several issues compounding each other. My hope is the tuning guide I put in post #21 would help clarify some things & give us a common language to discuss “cause & effect.” From your last post, with you outlining exactly what the car is doing ... sounds like it worked.

Let's go back to the beginning. Before you starting tuning on your car, it had a push condition. You didn’t mention what type of driving you were doing … road course, AutoX, etc. But I suspect your push condition showed up on tighter corners that required more steering input.

Your 51/49 F/R weight balance is great. Your initial baseline spring & sway bar package was close ... not optimum … but in the ballpark.

The “push” was the effect. The “cause” was a combination of:
1. Rear tires with 23.6” of tread versus front tires with 19.6” of tread.
2. Front end geometry … caster, camber, spindle KPI/SAI & toe … that is MUCH better than stock, but not optimized for tight cornering at a competition level.

Then, with the goal of fixing the problem …
3. You tuned in the wrong areas, that were not causing the problem … I’m trying to be gentle here … and went the wrong way with stiffer front springs, bigger rear ARB & smaller front ARB … compounding the problems. But hey, we all have done that & learned from it.

-----------------------------------------------------------------------------------------------------

Let’s expand on #1 …
You have 4” less tread in the front. That’s a 20.4% static tread difference. That’s 20% LESS grip for the front tires, than the rear.

Digest that a moment.

Any properly set up competition car, especially with a nice 51/49 weight balance like yours, will make the front tires push when driven to their limits … with 20% less tread in the front.

I’m not saying you can’t free up the rear end … reduce rear tire grip … to balance out the handling. You can … but some things to think about are:

1. We can't make a car optimum by reducing a positive quality (grip/tire traction) in one area to balance another weak area. Sometimes you have to … but my first inclination is to INCREASE the positive quality(grip/tire traction in this case) … in the weak area.

2. In other words, I suggest you not reduce the grip in the rear to match the front. Or, you might as well put 275’s all the way around.

3. My recommendation is to increase the grip in the front … to match the rear … for a balanced car ... WITH 20% MORE GRIP.

Make sense?

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I have 2 “by the ways” for you …

a. I had USAC Midget Race Cars that had 20% more rear tread width & they worked well, because they had 58% rear weight. Anytime a car has that much rear weight, the more speed carried into and/or through the corners, actually loosens the car up. That weight back there acts like a pendulum. So the 20% wider tires were needed there.

b. I’m building a street fighter for myself & I also like the cool look of the bigger rear tires than front tires. I have a set of 355’s in the rear & 285’s in the front for street cruising & car shows. But when I go run it often on road courses & autocross, it will have 335’s on all 4 corners, for more balanced performance.

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In production based cars, where the majority of the weight mass is on the front tires, usually around 52-56%. The last thing we want to do here is make the front tires have less grip than the rear. If it didn’t look completely dorky, we would put wider tires in front than the rear, to help make up for the poor weight balance.

Even in race cars, some class rules prevent or limit engine placement & weight placement and all the cars in that type of race class end up heavier on the front end. Crew Chiefs work to make these front heavy race cars handle neutral with suspension tuning. But the front end is the end that breaks free first when the car is driven past the tires’ limits ... because of this weight imbalance.

Wherever possible, practical & legal under race class rules, you want to design handling cars with as close to 50/50 weight balance as possible (with as much of the weight mass centered & inside the wheelbase.) There are no rules preventing us from optimizing our hot rods, other than our our own limitations of time, money & abilities.

You have an awesome 51/49 F/R weight balance. Great place to start. Currently your tires are 44.5/55.5 F/R ratio in contact patch on the ground … creating a traction capability of 44.5/55.5 F/R ratio. Your car is pretty weight balanced … but not traction balanced.

[Ron Sutton]

Matt, Let’s expand on #2 …

Cause …
I believe your caster, camber, toe & spindle KPI/SAI combination is not optimum for handling the tight corners of road course & AutoX competition. Specifically, the KPI/Caster split favors the KPI too much, and there is not enough camber & camber gain to fix it. It is WAY BETTER than stock geometry … just not optimum … yet.

It probably handles good on larger radius turns, because you’re not turning the wheels as far. But, when you’re hard into a corner … turning & braking … and then you turn the front wheels more … your tires tip & lean out … reducing the contact patch significantly.

In fact, not only is the tire’s contact patch with the road reduced, but you’re on the sidewall. Tire sidewalls are just like a spring .. really ... just like a spring. I use an Intercomp “Tire Sidewall Spring Rater” to learn the spring rate & characteristics of different tires. And they DO DIFFER.

77796


Effect …
In tight radius corners, the car goes into a push condition … until the car scrubs off enough corner speed that the tries regain grip.

When you have the outside front tire rolled over & bound up, it is overloaded … and it will break free … and hop … then regain traction … and continue this break free-hop-regain traction activity … although it is lessening each time as the car scrubs off speed … until the speed comes down enough that the front tires can hold.

The problem is …
When the KPI/Caster Split favors the KPI … the tire & wheel, on the outside of corners, goes into a state of positive camber (bad for the outside tire) … rolling over on the outside part of the tread and sidewall of the tire … with the inside part of the tread becoming unloaded. Basically, at this point, the actual tread making contact with the pavement (contact patch) gets narrower, making it incapable of maintaining the speed it was capable of an instant earlier, when it had a full contact patch.

The tire & wheel, on the inside of corners, goes into a state of negative camber (bad for the inside tire) … rolling over on the inside part of the tread and sidewall of the tire … with the outside part of the tread becoming unloaded. Also making the contact patch narrower, making it incapable of maintaining the speed it was capable of an instant earlier, when it had more contact patch.

So your front tires that were already offering 20% less traction than the rear tires … just got narrower … and lost even more front traction.

Hence … the push or understeer condition.

The amount of camber loss is minimal with slight amounts of steering input on large sweeping corners, but grows exponentially worse with higher rates of steering input (front wheel steering angle) on tighter corners.

We can discuss this further if you want to understand it better. Just ask.

[Ron Sutton]

Matt ... Let’s expand on #3 …

As outlined earlier ... the push condition was caused by front tires being 20% smaller than the rears & less than optimum front end geometry, causing the tires to lean out under hard turning, reducing the contact patch.

Most of the tuning changes you made did not address these problems and actually compounded the problems.

When you …
a. Stiffened the front spring rates … from 450# to 550# to 575# to 700# … you were reducing front end suspension travel and therefore reducing weight transfer & loading force onto the front tires … reducing the traction of the front tires in cornering situations.

b. Increased the rate of the rear ARB … combined with stiffer springs ... made the made the car run flatter … making it harder for the inside rear tire to disengage on corner entry ... making it easier for the big rear tires to overpower the much narrower front tires.

c. Decreasing the rate of the front ARB would normally allow the car to transfer more weight off the inside rear tire & onto the outside front tire helping it to turn … unless the car rolls so much it also unloads the inside front tire too. But the front springs were too stiff, not allowing much transfer … and the contact patch got even narrower as you turned the wheel further, due to geometry.

d. Increased the rate of the rear springs … this did not contribute to the problems. They were needed to reduce rear tire traction to help balance the front. But they will need to be softer once you work out your combination.


Reminder of the 20 CRITICAL TUNING CONCEPTS … with Key ones for Your situation in BOLD.

1. What you do WITH & TO the TIRES ... are the key to performance. Contact patch is the highest priority.

2. Geometry design, settings & changes should be to improve how the tires contact the road dynamically.

3. The design structure of every component affects how well that component handles forces inflicted upon it.

4. After the car is built, tires are selected & the geometry is optimum … most chassis tuning is to control the degree of weight transfer to achieve the traction goal.

5. Force (weight & weight transfer) applied to a tire adds grip to that tire. With the exception of aerodynamics, weight transfer from tire(s) to tire(s) is the primary force we have to work with.

6. Anti-Roll Bars primarily control how far the front or rear suspension (and therefore chassis) “rolls” under force, and only secondarily influences the rate of roll. Stiffer bars reduce roll angle, engaging the inside tires more.

7. Springs primarily control how far a suspension corner travels under force, and only secondarily influences the rate of travel. Shocks primarily control the rate of suspension corner travel under force, and only secondarily have influence on how far.

8. Springs, Shocks & Anti-Roll Bars need to work together “as a team” … with the springs’ primary role of controlling dive & rise, Anti-Roll Bars’ primary role of controlling roll & Shocks primarily role controlling the rate of both. They all affect each other, but choose the right tool for the job & create a harmonious team.

9. I find in production based cars, we can go no faster through a corner than the front tires can grip. Balancing the rear tire grip to the front … for balanced neutral handling … is relatively easy … compared to the complexities of optimizing front tire grip.

10. The front tires need force, from weight transfer on corner entry, to provide front tire GRIP. Too little & the car pushes … too much & the car is loose on entry. The rear tires need force, from weight transfer on corner exit, to provide rear tire GRIP. Too little & the car is loose … too much & the car pushes on exit.

11. Tuning to allow a suspension corner … to compress quicker or farther … provides more force & therefore more grip to that tire … up to the limits of the tire. Tuning to allow a suspension corner … to extend/rebound quicker or farther … provides more force & therefore more grip to the opposite corner’s tire … up to the limits of the tire.

12. Softer springs allow more compression travel & therefore more force onto the tire … for MORE GRIP on that tire ... and less grip on the opposite tire. Stiffer springs reduce compression travel & therefore lessen force onto the tire … for LESS GRIP on that tire ... retaining more grip on the opposite tire.

13. Optimum roll angle works & loads both sides of the car’s tires “closer to even” ... within the optimum tire heat range … providing a consistent "long run set-up" & optimum cornering traction throughout a multi-lap event. Long run set-ups typically take ½ a lap to a whole lap for the tires to “come in” 100%.

14. Higher roll angles work better in tight corners but suffer in high speed corners. Lower roll angles work better in high speed corners but suffer in tight corners. The goal on a road course with various tight & high speed corners … is to find the best balance & compromise that produces the quickest lap times.

15. Too much roll angle overworks the outside tires in corners & underworks the inside tires. Too little roll angle underworks the outside tires in a corner. Excessive roll angle works the outside tires too much … may provide an “ok” short run set-up … but will be “knife edgy” to drive on long runs. The tire heat up quicker & go away quicker. If it has way too much roll angle … the car loses grip as the inside tires are not being utilized.

16. Too little roll angle produces less than optimum grip. The car feels “skatey” to drive … like it’s “on top of the track.” The outside tires are not getting enough load from force, therefore not gripping enough. Tires heat up slower & car gets better very slowly over a long run as tires gain heat.

17. I learned early on that tuning is NOT linear 2 directions with stops at the ends. A car can be loose because it has too little roll angle in the rear & is not properly loading the outside rear tire ... or loose because it has too much roll angle in the rear & is not properly loading the inside rear tire. A car can be pushy because it has too little roll angle in the front & is not properly loading the outside front tire ... or pushy because it has too much roll angle in the front & is not properly loading the inside front tire.

18. The car’s Center of Gravity acts as a lever on the Roll Center … separately front & rear. Higher CG’s and/or lower RC’s increases roll angle. Lower CG’s and/or higher RC’s decrease roll angle. Getting the front & rear of the car to roll similar is desired. Getting them to roll the same is not, because …

19. Goal: To have optimum grip on all tires and disengage the inside rear tire (to a degree) to turn well … then re-engage the inside rear tire (to a higher degree) for maximum forward bite on exit. So, on entry & mid-corner, the car needs to roll less in the front to keep both front tires engaged for optimum front end grip, while allowing the car to roll slightly more in the rear to disengage the inside rear tire, to a small degree, to turn better. For optimal exit, the car will have more roll in the front & less in the rear to re-engage the inside rear tire to a higher degree than it was on entry & exit, for maximum forward bite (traction) on exit.

20. Don’t forget the role & affects the engine, gears, brakes, driver & track conditions each have on handling.

[Ron Sutton]

Matt,

Solutions:

1. Match the tire widths on all 4 corners & keep the front track no more than 1” wider in the front.

2. Add several degrees of positive caster & a small amount of negative static camber. I can expand on this more if you want to understand it better. Just ask.

3. After you put the 315’s on all 4 corners & improve the front end geometry, start with your initial spring & ARB combo of:

Front Springs: 450#
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 344#
Notes: The car had pretty good bite and turn in, but it was wearing the outside tires badly and it was the tire was being overloaded because it would skip, or hop once before taking a set.

Plus … keep the JRI shocks.

This baseline combination will most likely need to be “tuned” to the track & your driving style. But this package is good baseline.


----------------------------------------------------------------------------------------------------------

Tuning Tips after making the suggested changes …

Finding the “happy window” for the Roll Angle is key.

Your spring & ARB’s combine to create a term called Total Roll Stiffness, discussed in post #21. The optimum TRS is different for different tracks and/or corners. Softer TRS work better in tight corners but suffer in high speed corners. Higher TRS work better in high speed corners but suffer in tight corners. The goal on a road course with various tight & high speed corners … is to find the best balance & compromise that produces the quickest lap times.

Your goal with the ARB’s is to achieve a front Roll Angle that keeps both front tires working optimally … and a rear Roll Angle that allows the IR tire to disengage “slightly” … on corner entry & middle … and re-engages the IR tire more on corner exit.

The term for this is Roll Couple. Although the term sounds different … it is simply breaking the TRS into front & rear %. You want the Front Roll Couple % (front spring & ARB combined stiffness) to be higher than the Rear Roll Couple % (rear spring & ARB combined stiffness). Most race engineers will tell you 5% more than the front weight percentage is a good place to start. In your car, with 51/49 F/R weight … that means a good baseline would be 56% Front Roll Couple % and 44% rear … adding up to 100% of the TRS #.

Don’t get too lost in the numbers or terms. They’re just a starting point anyway, and every car needs to be “dialed in” with tuning to optimize the handling for your wishes & planned uses. I’m not trying to make you a race engineer. But I know you’ll have more fun with your car if it handles well when you're competing with it or simply driving it hard.

Basic Tips:
If the car has too much Roll Angle … use the right tool … and increase the ARB size … keeping the front ARB rate significantly stiffer than the rear ARB rate. If you think you need to increase the rate of the rear ARB to near the rate of the front ARB, you have other problems.

If the car is loose on entry … consider the Roll Angle first … and if it’s good … then stiffen the front spring rate. If it is tight/pushy on entry … consider the Roll Angle first … and if it’s good … then soften the front spring rate.

If the car is loose on corner exit … consider the Roll Angle first … and if it’s good … then soften the rear spring rate. If it is tight/pushy on exit … consider the Roll Angle first … and if it’s good … then stiffen the rear spring rate.

Yes, each of these changes will have effects on other areas. There is no “perfect handling car” when driven at its limits. That’s why they’re called “limits” ... and why this is so challenging. The top Crew Chiefs & Tuners … that dial in the best balance, fastest compromise & win races … are highly sought after & well compensated.


That's all for tonight. Let's pick the conversation up tomorrow.


As always, if anyone wants to chime in or ask questions, feel free to.

Ron Sutton

[rustomatic]

I think Ron is the new Ray (who seems to have left us recently). Ray is of course our site's dictionary of odd suspension/race car prep knowledge.

Ron, you have many thanks (and undoubtedly new fans/students) here, and you're even kind of local to me, which may be a plus . . . as I ponder the mess I made in my Falcon's first autocross (didn't spin out, and beat many douchey high-dollar cars, including an AMG Merc and some late model Corvettes with lousy drivers), after having it semi-decently sorted for the twisty roads...

What are your thoughts on the long (tranny output) torque arm, as opposed to the shorter circle-track type?

[Ron Sutton]

Rustomatic ... when you say "circle track type" ... I think you're referring to a 3-link. Correct?

Assuming each type of rear suspension is set-up correctly, rod ends spaced away from brackets properly with high misalignment bushings & clocked correctly ... the 3-Link & Torque Arm suspensions both allow the rear axle to articulate (roll angle in relation to frame) quite well, which is key for a handling car. Both 3-Links & Torque Arm suspensions require a device to keep the rear end centered in the chassis, like a panhard bar or watts link, so that is the same.

Torque Arm & 3-Link suspensions are similar in that they both have 3 mounting points & both use two lower trailing arms (or "control arms"). If the lower control arms are adjustable, then rear steer or roll steer can be adjustable with both.

But the difference with how & where the 3rd link/arm mounts is significant. As you know, the upper link of a 3-Link typically mounts on top of the housing (centered or offset) with pivoting rod ends ... whereas the torque arm mounts solidly to the housing & extends quite far forward (closer to the center of the wheelbase) with it's 3rd pivot point.

The key difference between the two ... is adjustability of the front Instant Center, rise leverage & anti-squat.

Torque Arm suspensions are common as a factory style rear suspension in some cars, because they are the simplest of the designs, allow a high degree of rear end articulation & can take high shock loads from hard launches. Their Instant Center, if designed properly, is automatically in a "good" spot ... and can be made "a little" adjustable ... but offer the least adjustability of the common PT rear suspension designs, for tuning the front Instant Center, rise leverage & anti-squat. These make a great all around suspension for the person that doesn't want to tune much.

3-Links can handle drag racing up to a point, but it wouldn't be my choice if the car was planned for high hp, high rpm, clutch dropping, slick running, wheelie pulling launches ... as there are only 2 rod ends "pulling" to lift the whole car.

Centered 3-Links are common in oval track racing & offset 3-Links are very common in road racing, especially in full body cars like GT1 & the Trans Am series, because they allow for a high degree of articulation & are highly adjustable & tunable for track conditions. You also see them a lot on top AutoX racers. 3-Links can be very adjustable if designed & installed with multiple or variable mounting points. Many "street kits" are sold with little or no adjustment to protect non-tuning novices from themselves.

There are pros & cons both ways. If designed right, Torque Arm suspensions may not be optimum, but will always be in the ball park, and are difficult, if not impossible, to tune yourself out of the happy window. If you know chassis set-ups & tuning ... or plan to learn ... and want a rear suspension with a high degree of tuning adjustability, to fine tune & optimize your rear suspension's performance, the 3-Link is the better choice. If not, it makes more sense to go with the Torque Arm suspension.

Personally, for my car, the choice is an adjustable 3-link for AutoX, Road Course track days & street driving.

Ron Sutton

[QuarterD25]

Rodney, I prefer ninja, not jedi...those dudes are wierd, thinking they can move things with their minds...

Ron, thank you for replying.

There is a lot to digest in the previous posts.
I feel that my current set up should be doing much better than it is now. I feel like the front is not set up quite right. From what I gather, I need to start taking measurements of everything. The KPI/SAI, is this just measuring from the middle of the holes on the spindle to where the control arms attach or where the ball joints pivot?

Also, a couple of questions on some things you said.

- Add several degrees of positive caster & a small amount of negative static camber. I can expand on this more if you want to understand it better. Just ask.

I get what caster is and that it makes the wheels want to center themselves more but what other effects does it have?

-When you have the outside front tire rolled over & bound up, it is overloaded … and it will break free … and hop … then regain traction … and continue this break free-hop-regain traction activity … although it is lessening each time as the car scrubs off speed … until the speed comes down enough that the front tires can hold.

How do you know when this is happening? What are they symptoms? How do you fix this?
I am using NTO5's right now. I run 32/30 (ish) on the tires for autox and the one road course I have done. They have some wicked wear on them from what I think is alot of neg camber. The car seems to either push or hop/skip when i have some speed going into corners. The last autox I did, I took out he same row of cones a couple of time while trying to maintain speed. I felt bad for the corner works there.

[High Plains Mopars]

Mind blowen....

Yupper, Vehicle dynamics get pretty complex pretty quick.

Ron, thanks for explaining all this.

[Ron Sutton]

Ron, thank you for replying.
No worries. Glad to help.


There is a lot to digest in the previous posts.
Yup, yup. Competition cars are complex.

I feel that my current set up should be doing much better than it is now. I feel like the front is not set up quite right.
For competition purposes ... your car sure didn't start out right from the factory, so unless you made it right, it's safe to say it's not.

--------------------------------------------------------------------------------------------------------------------

From what I gather, I need to start taking measurements of everything.
That depends on what you want to do, how deep you want to get involved in improving it & how far you want to take it. You don't have to go to all that work if you want to achieve moderate improvements & enjoy a better handling car.

But if you want to kick ass & take names at competition events, you have a LOT of WORK to do. Pack a big lunch, to go along with a serious commitment to learning, working, tuning, testing, more tuning, more work ... and more testing. I think the key is being clear on your personal goals, before you dive in.

--------------------------------------------------------------------------------------------------------------------

The KPI/SAI, is this just measuring from the middle of the holes on the spindle to where the control arms attach or where the ball joints pivot?
KPI stands for King Pin Inclination & SAI stands for Steering Angle Inclination. They mean the same thing. KPI was a term coined back in the day of solid front axles when spindles actually used king pins.

Steering Angle Inclination is a more correct modern term & is calculated simply by running a theoretical line through the upper & lower ball joints & comparing that angle to the rolling axis of the tire & wheel.

If the tire were straight up with 0.0° camber ... & you find the angle of the theoretical line running through the upper & lower ball joints ... that is the KPI or SAI depending on what term you prefer. (I use both terms because many race car guys are used to the older term of KPI.) See photo.


77811


--------------------------------------------------------------------------------------------------------------------

Also, a couple of questions on some things you said.
- Add several degrees of positive caster & a small amount of negative static camber. I can expand on this more if you want to understand it better. Just ask.
Before we go any further ... it is dangerous to simply use advice intended for another car. Because front end geometry his all about the right combination, no 1 part of that geometry is the magic elixir.

I suggested that for Matt, because I know he has a DSE clip, which are well designed, utilizing a C6 spindle with 9.15° KPI/SAI, 5° of caster & -0.5° camber, with small amount of caster & camber gain built in.

I do not know what any of your geometry is, so I have no idea if that suggestion is correct for you … yet. But if you'll get me your specs, I'll be glad to guide you. I just don't want you ... or anyone reading this ... to take a suggestion meant for someone else’s specific application as gospel & run with it.

--------------------------------------------------------------------------------------------------------------------

I get what caster is and that it makes the wheels want to center themselves more but what other effects does it have?
Caster ... creates Camber as you know it ... but only when the wheels are turned. As you know, to achieve caster, you're moving the upper BJ back, and/or the lower BJ forward to "lean" the spindle back.

The "lean back" is measured in degrees & called positive caster. As you turn the steering wheel, caster leans the top of BOTH front tires back & towards the inside of the corner ... basically adding what you think of as camber to the tires.

Combine this with the static camber & camber gain through suspension travel and these are your tools to get the tire tread to lay flat for maximum tread contact patch during hard cornering.

--------------------------------------------------------------------------------------------------------------------

-When you have the outside front tire rolled over & bound up, it is overloaded … and it will break free … and hop … then regain traction … and continue this break free-hop-regain traction activity … although it is lessening each time as the car scrubs off speed … until the speed comes down enough that the front tires can hold.

How do you know when this is happening? What are they symptoms?
If it is minor ... you'll feel & see the car pushing from inside the car ... and a trained eye or video camera can catch it from outside the car. If it is significant, you'll also feel it in the steering wheel.

How do you fix this?
The key to making a competition car carve corners well, is keeping both front tires’ full contact patches on the ground while cornering, regardless of steering angle. This is achieved with optimum front suspension geometry, which is often discussed but rarely fully understood.

This specific problem is generally caused by too much KPI/Caster Split … meaning the degree of KPI angle is much greater than the degree of positive caster. The greater the KPI/Caster Split … the more the top of both front tires tilt the WRONG direction when turned. The amount of camber error is minimal with slight amounts of steering input on large sweeping corners, but grows exponentially worse with higher rates of steering input (front wheel steering angle) on tighter corners.

The tire & wheel, on the outside of corners, goes into a state of positive camber (bad for the outside tire) … rolling over on the outside part of the tread and sidewall of the tire … with the inside part of the tread becoming unloaded. Basically, at this point, the actual tread making contact with the pavement (contact patch) gets narrower, making it incapable of maintaining the speed it was capable of an instant earlier, when it had more contact patch.

The tire & wheel, on the inside of corners, goes into a state of negative camber (bad for the inside tire) … rolling over on the inside part of the tread and sidewall of the tire … with the outside part of the tread becoming unloaded. Also making the contact patch narrower, making it incapable of maintaining the speed it was capable of an instant earlier, when it had more contact patch.

Hence … the ugly, frustrating, painful & embarrassing push (understeer) condition.

--------------------------------------------------------------------------------------------------------------------

I am using NTO5's right now. I run 32/30 (ish) on the tires for autox and the one road course I have done. They have some wicked wear on them from what I think is alot of neg camber.
Are they worn worse on the inside or outside edges of the tire?

Regardless, that is your clue the tires are REALLY unhappy, meaning not running with flat, Full contact patches. However wide your front tires are ... you’re only using a portion of that width & available grip.

--------------------------------------------------------------------------------------------------------------------

The car seems to either push or hop/skip when i have some speed going into corners.
Sounds like your KPI/Caster Split favors the KPI too much … but I don’t know for sure until I review your geometry specs.

--------------------------------------------------------------------------------------------------------------------

The last autox I did, I took out he same row of cones a couple of time while trying to maintain speed. I felt bad for the corner works there.
What about those poor little orange cones? They’re probably traumatized!

I just hope they don’t change careers & end up working on a highway project like prison convicts.

:drive1:

[Ron Sutton]

Yupper, Vehicle dynamics get pretty complex pretty quick.

Ron, thanks for explaining all this.

Glad to help.

[rustomatic]

Ron, as expected, you've provided great feedback on my 3-link/torque arm quandary--I've been drooling over torque arms lately, but packaging space and reality on a '63 Falcon are tough games. Thanks! I'll be studying up more on people's cars in Marina this weekend, at the American Autocross Series. Cheers!

[Ron Sutton]

I'm unclear why your car has packaging issues for a Torque Arm suspension. Some cars have a hard time fitting in a long enough upper link for a good 3-Link set-up. But most Torque arms go under the floor plan.

Enlighten us why you're having space problems. Thanks !

[j-rho]

Moved here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas) for Matt's sake

[Ron Sutton]

This post topic moved to another thread here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas).

[SSLance]

All I need now is for Ron to explain "wedge" and I'll have everything I need to go NASCAR racing... ;)

Seriously, does anyone else feel like they are stealing by reading all of this information here on a free public forum?

Props to you Ron!

[Matt@BOS]

Hey Ron, I have another round of questions for you.

After giving your opinion of what would be a close to optimal setup, I was a little curious about your opinion about how much spring is needed to support the weight of a car. Do you like pre-load on springs, or not. What effect does it have? If you wouldn't mind elaborating a little bit more, I'm sure it could benefit us all.

The reason I ask is because you recommended 450lb springs up front, and 250lb springs out back. The front springs and .250" sway bar with my current setup have not been able to control the roll to a degree that I've been happy with, and tend to settle so much that I would need to run a longer spring than I can fit on the coilover without compressing the longer spring to get in under the shock collar.

Matt

[Ron Sutton]

All I need now is for Ron to explain "wedge" and I'll have everything I need to go NASCAR racing... ;)

Seriously, does anyone else feel like they are stealing by reading all of this information here on a free public forum?

Props to you Ron!

I'm taking a little time off from racing ... before I tackle my next project ... and I enjoy sharing & helping if someone is actually going to use it.

Were you serious on the"wedge" question ... or just being funny?

[Ron Sutton]

Matt, I need some more clarity,

Hey Ron, I have another round of questions for you.

After giving your opinion of what would be a close to optimal setup, I was a little curious about your opinion about how much spring is needed to support the weight of a car.
I'm NOT clear on what you're asking. Can you re-phrase this? :confused:

Do you like pre-load on springs, or not.
Until I read further down, this question confused me more ... because all springs are preloaded with the weight of the car. :rolleyes:

What effect does it have? If you wouldn't mind elaborating a little bit more, I'm sure it could benefit us all.
Again, all springs get preloaded with the car's weight & I'm not clear on what you're asking. Are you asking ... is there a problem with running a spring that has to be compressed to install it on the shock? or ... ?

The reason I ask is because you recommended 450lb springs up front, and 250lb springs out back. The front springs and .250" sway bar with my current setup have not been able to control the roll to a degree that I've been happy with,
OK. Let's discuss higher rate sway bars & springs. But I need your shock mounting motion ratio & shock angles to do this correctly.

and tend to settle so much
What do you mean settle? "Settle" in spring lingo ... means the springs started out a "X" free height (no load) ... and after being installed and used ... are now a shorter free height when removed. Is that what you mean? Or are you calling the compression of the spring with the car's weight "settling" ... when in fact their free height is the same as before?


that I would need to run a longer spring than I can fit on the coilover without compressing the longer spring to get in under the shock collar.
Two things ...
1. Why would you need to run a longer spring?
2. When you ran this spring before, did the car sit too low?

[SSLance]

Truthfully I always wondered exactly what the nascar teams were talking about when discussing putting wedge into the car?

[j-rho]

Moved here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas) for Matt's sake

[Ron Sutton]

WoooHoooo !!

My little buddy AJ Allmendinger won the NASCAR Nationwide race at Road America!

Couldn't be happier for him. He needed something good to happen.

[Ron Sutton]

Truthfully I always wondered exactly what the nascar teams were talking about when discussing putting wedge into the car?

Hi Lance,

"Wedge" is a Stock Car term meaning the same thing as "Cross Weight" used by Road Racers & Open Wheel Racers, even in oval racing. Some racers simply shorten it to "Cross" ... as in "put some cross in the car". Then throw in a mix of Engineers and it's a wonder any of them understand each other. :rotfl:

I have to go back & forth because I've been involved heavily in different forms of oval & road racing. I find it amusing the terms are so different. One of them you & I have been discussing is KPI & SAI. Stock car guys still use the KPI term, but Double A-arm cars don't have king pins.

Anyway, let me explain what Wedge & Cross Weight are ...

If we were going road racing, and the rules allowed, we would be running the car as weight balanced side-to-side as we could get it. Here is a car that weighs 2572#, with a 48.77% front weight & 51.23% rear weight.

--------------------------------------------------------------------------------
Example #1

If we could achieve it, the 4 scales would read ....

LF 626 # RF 626 #
LR 660 # RR 660 #

This is a car with no wedge or cross weight.

--------------------------------------------------------------------------------
Example #2

If that same car was on the scales & read ...

LF 616 # RF 636 #
LR 670 # RR 650 #

You'll notice the LR & RF corners weigh more than the RR & LF. That is wedge or cross weight. In this example, the front wheels have a 20# difference between them ... as do the rear tires. That's not much, but not optimum. Not counting other aberrations in the suspension, this car would have a little more grip on left hand turns & a little less grip on right hand turns.

It's not much, but when you're racing and driving the car at 102% & the tires are at their optimum slip angle ... with no room to spare ... 20# would make a small difference that would affect the car "a little" & a talented race driver would feel ... and be whining & screaming for a change. :attn:

OK, just kidding on the whining & screaming ... sorta. You NEED the driver to give accurate, precise, measured feedback in a consistent, methodical way to know when to tune, which direction to go & how much. The difference between "whining" & "constructive input" comes down to attitude & communication skills ... and varies from driver to driver.

--------------------------------------------------------------------------------
Example #3

LF 636 # RF 616 #
LR 650 # RR 670 #

If it were reversed ... and looked like the #'s above ... again not counting other aberrations in the suspension, this car would have a little more grip on right hand turns & a little less grip on left hand turns. If the car handling was "neutral" on right hand turns, it would be a bit looser on left hand turns. If the handling was "neutral" on left hand turns, it would be a bit tighter/pushy on right hand turns.

--------------------------------------------------------------------------------
Example #4

Both examples #2 & #3 show SMALL amounts of cross weight difference. Bigger differences in corner weights make bigger differences in the results, but the effects are the same.

LF 736 # RF 516 #
LR 550 # RR 770 #

If the differences were larger ... like the example above ... the handling differences from right turns & left turns would be HUGE.

If the car handling was "neutral" on right hand turns, it would be a VERY loose on left hand turns. If the handling was "neutral" on left hand turns, it would be VERY pushy on right hand turns.

By the way, this example is not a simple tuning adjustment.

--------------------------------------------------------------------------------

In most cases, it is undesirable to have any cross weight for road racing or AutoX cars. There are exceptions.

Years back, we raced at a shifter kart track that had a LOT of fast right handers & only 2 lefts. 1 of the left turns was banked ... which gave more grip ... and the other left hander was a tight hairpin. We dialed in cross weight the opposite of an oval track car, so it had more grip on right hand turns. The banked left hander was still good. And the karts were loose in the hairpin ... which we used to our advantage, rotating the rear end to help the karts turn. That set-up dominated there the 2 years we ran it.

--------------------------------------------------------------------------------
Example #5

LF 516 # RF 736 #
LR 770 # RR 550 #

So, the casual observer may think oval track racers simply add "wedge" and it would look like this.

You calculate how much wedge or cross weight a car has ... by adding the opposite corners of LR & RF & compare it the car's total weight.
The LR 770 # + RF 736 # = 1506# / Total: 2572 # = 58.55% wedge or cross weight.

* Example #4 would be described as having 41.45% wedge or cross weight.

--------------------------------------------------------------------------------

But that's not how an oval track car would look on the scales ...
because they are allowed to race with a higher left side weight balance. Each series or class has a rule written as either a left side percentage maximum, a left side pound maximum or specific rules about where weight can be put.

In Professional Road Racing & Oval Track Racing, car designers & builders build the cars as light as they can ... and still be structurally sound ... so they can put the weight (lead or tungsten) where they want it. Low, left & centered in the wheelbase for Oval Track ... Low & centered for Road Racing.

Here is what the scales would read for a real world oval track car with rules calling for a Maximum of 58.0% left side weight, if it still had the same & 51.23% rear weight we have been using in the previous examples.

LF 616 # RF 637 #
LR 880 # RR 436 #


This car weighs a total of 2572# ... with driver & 175# Lead
Target Cross: 59.0% w/ARB preload
* It was 57.5% before preloading the front ARB :secret:

Left side weight: 58.2% :evil:
Front weight: 48.77%
Rear weight: 51.23 %

--------------------------------------------------------------------------------

So when a Stock Car team is calling for more wedge, they are turning a threaded adjuster "in" on the LR or "out" on the RR ... that is to give the car more grip. If they're calling for less wedge, they are turning a threaded adjuster "out" on the LR or "in" on the RR ... that is to free the car up (less grip).

They do both of these through the back window.
* The right side of the track bar is also adjustable through the back window.

--------------------------------------------------------------------------------

Oval track racing is way more challenging than outsiders know. I love all forms of motor racing ... but I prefer road racing the most.

[Ron Sutton]

This post topic moved to another thread here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas).

[j-rho]

Moved here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas) for Matt's sake

[diesel25lrs]

Ron,
Thank you so much for sharing your knowledge! I've been asking many of these same questions & basically have the exact same issues as Matt but with a Speed Tech torque arm setup... My build started as a restoration that quickly turned into auto-x racer & wondering why the "REALLY" bad push in corners...everyone would just tell me to slow down going into corners...yes- some of it is inexperience driving but i feel it was more the cars bad setup...The car wasn't built correctly from the start for racing(275F/345R tires & stock spindles)...with almost everyone on the auto-x scene switching to wider fronts the last year it really got me thinking about my setup & reading this has really confirmed where i need to start making improvements to go faster! So i dont highjack this thread- i'll reread everything again & go along for the ride! I would like to get back with you at a later time with my specs for setup if possible? Thanks for breaking everything down!
Josh

[Ron Sutton]

Ron,
Thank you so much for sharing your knowledge! I've been asking many of these same questions & basically have the exact same issues as Matt but with a Speed Tech torque arm setup... My build started as a restoration that quickly turned into auto-x racer & wondering why the "REALLY" bad push in corners...everyone would just tell me to slow down going into corners...yes- some of it is inexperience driving but i feel it was more the cars bad setup...The car wasn't built correctly from the start for racing(275F/345R tires & stock spindles)...with almost everyone on the auto-x scene switching to wider fronts the last year it really got me thinking about my setup & reading this has really confirmed where i need to start making improvements to go faster! So i dont highjack this thread- i'll reread everything again & go along for the ride! I would like to get back with you at a later time with my specs for setup if possible? Thanks for breaking everything down!
Josh

You're welcome Josh. After you re-read all the tech stuff ... if you have questions pertinent to this thread ... feel free to chime in here. If you have questions concerning your car & specific handling issues & solutions, let's start a new thread.

What part of NC are you in? I travel to the Mooresville & Concord area occasionally.

[diesel25lrs]

Ron,
Sounds great! I'm just south of Raleigh about an hour in Pinehurst. M-ville is only 2hrs from here... You must be doing some NASCAR tar testing over that way...

[RobNoLimit]

great info Ron. I enjoyed talking with you in P-town (I have the red C10) Thanks for helping out. Some of the tuning points for Matt have me thinking.:smoke:

[Ron Sutton]

Ron,
Sounds great! I'm just south of Raleigh about an hour in Pinehurst. M-ville is only 2hrs from here... You must be doing some NASCAR tar testing over that way...

Josh,

That was funny. No, we're not doing "Tar testing".

I still work with Penske, Roush, RCR & Gibbs on sponsorship stuff I can't discuss publicly. I expect to fly back there again in August. Often I fly into RDU because I have a zillion Southwest Air points & they don't fly into Charlotte. Flying into RDU makes it easier to go to RCR first, then spend my time in Concord, Huntersville, Mooresville, etc. I like to stay in Concord, by the Mall, because there are so many restaurants and it's close to the dirt track, Concord Speedway's two tracks & the big Speedway.

Is there any cool ProTouring stuff or AutoX going on back there?

[Ron Sutton]

great info Ron. I enjoyed talking with you in P-town (I have the red C10) Thanks for helping out. Some of the tuning points for Matt have me thinking.:smoke:

Hi Rob !

I enjoyed talking with you too. I love your truck. My best buddy has a sweet '69 C10 short fleetside that I have first dibs to buy when he's ready to sell. I'll probably paint it red & black, since those are my colors.

You have a great chassis & suspension package. I would love to work with you on set-up and/or geometry stuff ... and go do some test days if you want. We might find a few more tenths with some TLC.

[diesel25lrs]

Ron,
Yeah-thats the racer's haven over there! Let me know when your coming for sure & i'll cruise the hotrod up & grab some dinner with you!

We have a few good races around here- RTTOS in SC, RTTH- pigeon Forge, TN, GG-Charlotte & of course DSE HQ is just outside of Charlotte- must see if u haven't been there yet! I have about 4 good friends within an hour of me that all have PT cars so the scene is not huge but growing here!

[Ron Sutton]

I'll do that. Take care.

[Ron Sutton]

Matt sent me a PM, and said I could post it to respond so everybody could learn from what we’re discussing.

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Hey Ron, Let me provide you with a little more clarity. I apologize if my terminology is incorrect. Most of us come from a hot rodding, show car building, or cruising background and it is only in the last several years that we've started to realized how much fun it is to try and go fast, at least that is the case with most of us southern California guys. I think we have probably come up with some of our own terms as we go.

What I meant by pre-load was the amount of load placed on the spring before the car is ever placed down on its own weight, or how much I need to compress the spring before I put the coil over back in the car.
Gotcha. I understand what you’re saying now.


For example, on the front, with 450lb springs I would need to tighten the collars way up so that the spring is already moderately compressed in order to keep the car from sitting too low. If I only ran the bottom adjustment collar up to the spring before setting it in the car, the car would sit far too low. Does that make a little more sense.
Yes. I’m clear now.


Perhaps I need a longer spring?
The question to get answered for both of us is … if you compress either front suspension corner … does the spring run out of travel first or the shock? Then that will guide me on what to suggest.


Also I have noticed that with the lighter springs, 450 and 550 that the car would sit lower after the car was driven on the track for the first time. I could drive 200 miles and ride height would stay the same, but after an afternoon at the track the front would sit half an inch lower, and stay there permanently. Is that normal?
It is normal on low quality springs. Most … but not all … of the $50-75 springs typically do that. What brand of springs are your 450#’s? … what brand are the 550#’s ?


I think from my seat time the car felt undersprung (at least to me). With about a degree of static negative camber I was still chewing up the outside of my front tires.
This is partially a Roll Angle issue … to be worked out with springs & sway bar … and partially a KPI/Caster split issue.

Your DSE setup is WAY better than factory, but doesn’t currently have enough caster to be optimum for AutoX cornering level performance. I’ll expand on this, but you will want to refer back to the post I made on KPI/Caster Split for it to completely make sense. DSE and many others top companies building clips use the Corvette C6 spindle which has 9.15 degrees of KPI. To dial that front end to CARVE tight corners, we need around 1.0+ degrees more caster then the KPI angle.

The ZR1 C6 Corvettes that run this spindle have a factory caster setting of 7.7 degrees up to 8.3 degrees … for factory production street cars. All of the savvy Corvette guys that compete with these cars, run the caster at 10.0 to 10.5 degrees … then make the camber around -1.5 … and kick butt.

I am not sure why the clip companies reduce their standard caster setting below factory specs, but probably have good reasons for it. For performance, I would think they would run the factory setting the spindle was designed for … around 8 degrees, but again, they may see other reasons not to. If we want it to really kick ass in AutoX, need to use the settings Corvette racers use (-10.0 to -10.5 degrees).

I don't have permission to say who … but several winning AutoX guys … run a LOT of caster. Matt, currently, at 5.0 degrees of caster, your KPI/Caster split is 4.15 degrees favoring the KPI. To achieve optimum tire contact patches … the KPI/Caster split needs to be 1.0 or more degrees favoring the Caster.

Having said that, I’m not sure your current DSE package can “get to” 10+ degrees of caster … and that’s ok. Let’s just make it better than it currently is. If you can get yours up to 7-8 degrees of caster … and set the static camber around -2.0 degrees … you won’t be folding the tire under like the car in the attached photo.


77974

[Ron Sutton]

Part 2 of Matt's questions & my answers

I think I was actually most happy with 550lb springs, because, in retrospect, they provided better response in autocrosses, seemed to work effectively out at Willow Springs (the car never felt too skiddish or harsh) and held the weight better. I also know that DSE has switched from running 450 to 550lb springs on their subframes.

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The discussion about springs is quite involved. More than most people would think … with something as seemingly simple as springs.

This is going to be controversial … because there are new* concepts … and there will be people who have run traditional** spring packages for decades … that have worked well for them … they have been successful with traditional** spring packages … and they don’t understand the new concepts & technology.

*New as in the last 20 years
**Traditional as in, since the 1950's

When anyone has run something for years … that has worked well for them … changing to something new & “supposedly” better … and re-learning new concepts … doesn’t come easy. For those following along with Matt & I … I’m not suggesting you change anything. I’m simply willing to share these somewhat new, yet vastly proven suspension concepts with you … and you can decide what you want.

Now is as good of a time as any to discuss it … since you (Matt) need to make some spring & ARB decisions.

Matt … and fellow readers … you can learn about this … and simply go with what makes sense for you & what works best for your goals. That’s a cool thing about hot rodding. One guy goes 3-link, another chooses a torque arm & another yet is debating over 3 versions of 4-links. And we all can be happy, enjoying our cars. Even competing against each other at an AutoX or track day event.

What I really care about … in helping you learn this … is that you have fun with it … and get your car to better achieve your goals. Not my goals. Not anyone else’s. I’m helping Lance make his Monte SS a better AutoX car, but we’re NOT cutting it up & putting a race chassis in it. Just improving the suspension to achieve his goals. Matt, my goal here, is to help you achieve your handling goals with your car.

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Let’s get started with some key concepts for springing a car:

Weight transfer: Speaking literally … weight doesn’t transfer. I mean weight doesn’t unbolt itself and move around the car, re-attaching itself somewhere else just because you jumped on the brakes … I mean other than your coffee cup. :doh:

What is really happening is the car’s weight mass at the CG is acting on the roll & pivot axis of the car and applying “Force” when the driver tries to get the car to stop, turn or accelerate. Calling it “Weight Transfer” is not technically correct, but it is simple & easier for most of us to understand ... so we’ll call it Weight Transfer or WT for short. :)

Static weight & weight transfer (Force) combine to define the load on the car’s 4 tires. Load applied to a tire … adds grip to that tire. More load equals more grip … up to the point of overloading the tire. As we add load to one tire, we are reducing the load on another tire. Understanding this is key. Matt, you have 3500# to work with … and only 3500# to work with.

With the exception of aerodynamics, suspension components & geometry tuning is the primary toolset we have to work with in controlling weight transfer from tire(s) to tire(s).

Reminder: You’re not creating the Force. The Force already exists when you try to stop, turn or accelerate a 3500# car. When you step on the brakes, Force will make the front end want to compress (dive) & the back end want to lift … also known as “pitch.” You’re just using the tuning tools available to influence how fast & how far the front end dives & the rear end lifts. When you steer the car hard left or right … Force will make the car roll about its roll centers. You’re just using the tuning tools available to influence how fast & how far the car rolls. On corner exit, under power … you get it.

We have many tools to use, to influence chassis pitch & roll, including springs, sway bars, shocks, adjustable roll centers, weight placement, ride height, suspension arm or link geometry, track width, wheel base, etc, etc. Some are “built in” & some are tunable. For this post … I’m going to keep my discussion to springs, ARB’s (Sway Bars) & shocks.

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This next part is instrumental in understanding your role as a tuner.


Where weight is transferring TO … is loading the tire more … and increasing tire grip/traction at that tire. Where ever weight is transferring FROM … is loading that tire less … and decreasing tire grip/traction at that tire.


You need to optimize the “balance of the grip” of all 4 tires at each stage of the corner (entry-middle-exit). So you don’t want to over load some tire(s) & underload other tire(s). You’re tuning the car to find the optimum “balance of the grip.”


Tires are your only contact with the pavement. Grip is speed. Using all four tires will be faster than just using two. You just have to work out where to increase load/grip & where to decrease load/grip … and how much.


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So how do you put more load on a tire?
The further the suspension travels … the more weight is transferred TO that end or corner of the car, putting more load & grip on the tire(s) at that end or corner. And more weight is transferred FROM the opposite end or corner, reducing the load & grip on the tire(s) at that end or corner.

Here are some basic examples discussing hypothetically using ONLY SPRINGS as the tuning tool & ASSUMING the Roll Angle is kept optimum with other tuning tools.

As you brake in a straight line the front springs allow weight transfer from both rear tires to both front tires.
• Softer front springs allow the front end to travel more, putting more load/grip on both front tires & reducing load/grip on both rear tires.
• Stiffer front springs allow the front end to travel less, putting less load/grip on both front tires & retaining more load/grip on both rear tires.

When you brake & turn at the same time, the outer front spring primarily allows weight transfer from the inside rear tire to the outside front tire.
• Softer front springs allow more travel, putting more load/grip on the outside front tire & reducing load/grip on the inside rear tire.
• Stiffer front springs allow less travel, putting less load/grip on the outside front tire & retaining more load/grip on the inside rear tire.

When you are turning, with no braking force, the outside front & rear springs allow weight transfer from the inside tires to the outside tires.
• Softer front & rear springs allow more travel, putting more load/grip on the outside tires & reducing load/grip on the inside tires.
• Stiffer front & rear springs allow less travel, putting less load/grip on the outside tires & retaining more load/grip on the inside tires.
• Softer front & stiffer rear springs put more load/grip on the outside front tire & reducing load/grip on the inside front tire … while putting less load/grip on the outside rear tire & retaining more load/grip on the inside tires.
• Stiffer front & softer rear springs put less load/grip on the outside front tire & retaining more load/grip on the inside front tire … while putting more load/grip on the outside rear tire & reducing load/grip on the inside tires.

In most every situation in life & racing there are “exceptions to the rule” … this is one of them. What you read is not a typo. As you accelerate out of the corner, the inside rear spring WOULD allow weight transfer from the outside front corner to the inside rear corner … IF THE FORCE was going that direction. But it’s not. The Force … when accelerating out of a turn, while still turning … is to the outside & rear. So there is NO FORCE pushing the car onto the left rear … yet. BUT … for optimum acceleration you still need to utilize all the potential grip available with the inside rear tire. So …
• Stiffer rear springs keep the inside tire engaged more retaining more load/grip on the inside rear tire.
• Softer rear springs lessen the inside tire’s engagement more reducing load/grip on the inside rear tire.

As you unwind the steering to straighten the car, but are still accelerating, NOW there is weight transfer to the insider rear tire as the car flattens out.
• Softer rear springs allow the rear to travel more, putting more load/grip on both rear tires & reducing load/grip on both front tires.
• Stiffer rear springs allow less travel, putting less load/grip on both rear tires & retaining more load/grip on both front tires.

Did you notice some conflicts? That’s what makes this challenging in finding the best compromise … the best “balance of the grip.”

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Let’s clarify some things …

Corner Entry:
1. Softer front springs put more load & grip on the front tires for better turning ability.
2. Stiffer front springs keep more load & grip on the rear tires allowing the driver to drive into the corner deeper & brake harder.
3. Too soft of front springs do not allow the driver to go in as deep & brake as hard. Optimizing the brake bias & shock package helps.
4. Too stiff of front springs makes the car push on entry due to low load & grip on the front tires
5. Rear springs are left out, because their primary role here is working with the rest of the suspension for optimum Roll Angle.

Mid Corner / Roll Though Zone:
1. Softer front springs put more load & grip on the front tires … allowing for higher cornering speeds … allowing softer braking on entry.
2. Stiffer front springs keep more load & grip on the rear tires … requiring lower cornering speeds … requiring more braking on entry.
3. Too soft of front springs make the car loose in the middle of the corner due to low load & grip on the rear tires.
4. Too stiff of front springs makes the car push in the middle of the corner due to low load & grip on the front tires.
5. Rear springs are left out, because their primary role here is working with the rest of the suspension for optimum Roll Angle.

Corner Exit:
1. Softer rear springs put more load & grip on the rear tires for more traction.
2. Stiffer rear springs keep more load & grip on the front tires for better turning ability.
3. Too soft of rear springs can make the car push on corner exit to low load & grip on the front tires.
4. Too stiff of rear springs can make the car loose on corner exit to low load & grip on the rear tires.
5. Front springs are left out, because their primary role here is working with the rest of the suspension for optimum Roll Angle.

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On the menu today, your choice … pick just ONE.

• Stiffer front springs let you drive in deeper … but gets tight/pushy in the middle requiring lower corner speeds.
• Softer front springs require you to brake softer … but turns much better in the middle allowing higher corner speeds.

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Roll Angle vs Pitch angle

The car can’t run flat … it needs to travel … so it’s either got to Roll or Pitch … that’s the primary difference in the two tuning concepts I’m going to outline.

• It can’t pitch a lot AND roll a LOT … it would be dangerous & undrivable
• It can’t pitch AND roll a LITTLE … it would just skate on the road surface.
• It can pitch a lot & roll a little … OR it pitch a little & roll a lot

You need to pick a path … so here is what they look like.

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Conventional:
• Stiff front springs
• Small, soft sway bars
• More Roll
• Less Pitch

Sample Set-up:
Front Springs: 550-700#
Front ARB: 100-200#
Rear Springs: 150-200#
Rear ARB: 50-100# or … No ARB & 50-100# stiffer rear springs … or higher rear Roll Center


Old School – Let it Roll
• Moderate to High Roll Angle (3 to 6 degrees)
• Front suspension doesn’t compress much on entry. (3/4” to 1-1/2”)
• Load the outside tires for grip & unload the inside tires so it will turn.

Drawbacks:
• Too much roll angle overworks the outside tires in corners & underworks the inside tires.
• The tires heat up quicker & go away quicker, providing a better short run set-up.
• After tires “come in” the car is “knife edgy” to drive.
• Very line sensitive … drivers say, “can’t drive it just anywhere” … meaning it handles poorly out of its optimum groove.
• As the track grip increases & the car rolls more … these problems magnify.
• When it rolls a lot & you brake hard, the inside rear tire has no grip. So to prevent from being loose on entry you must run stiffer front springs.
• The stiffer front springs make the car tight/pushy in the middle … requiring the driver to brake more and run slower corner speeds.


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High Travel:
• Soft front springs
• Big, stiff sway bar in front
• Known as SS/BB … soft spring/big bar … if no bump stop or coil bind is utilized.
• Same concept used in conjunction with travel stops: Bump Stops or Coil Bind
• Less Roll
• More Pitch

Sample Set-up:
Front Springs: 300-400#
Front Springs: 200-350# with bump rubber or coil bind
Front ARB: 600-2000+#
Rear Springs: 300-500#
Rear ARB: 100-200# … or No ARB & 100-200# stiffer rear springs … or higher rear Roll Center

New School – Get the nose on the ground & run the car flatter
• Roll angle is minimal, controlled primarily by the sway bar in front & stiffer rear suspension. (1 to 1.75 degrees)
• Front suspension travels a LOT in dive (compress) to put maximum load & grip on front tires. (3” +)
• Load the outside tires only slightly more than inside corners for optimum 4 tire corner grip.

Disadvantages:
• Even when optimized … it still can not be driven as deep on corner entry as a conventional set up.
• When racing door-to-door in a field of race cars running a mixture of set-ups, the SS/BB set-up is susceptible to dive bomb passes.

Advantages:
• Flatter Roll Angle works the tires more evenly.
• The tires heat up slower & last longer … making a better long run set-up as the tires are “good” way longer.
• Less line sensitive … drivers say, “I can drive it just anywhere” … meaning any line on the track.
• As the track grip increases … the advantages show more.
• The soft spring/high travel front end puts creates maximum grip on front tires for highest cornering speeds.
• Will produce faster cornering speeds & quicker lap times over conventional set-up, all other things being equal.

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Tweener Set-ups:

Today I see guys that won on old school conventional set-ups “migrating” to some version of SS/BB with or without bump stops. They are on softer front springs than before & a few steps up in size in ARB. They’re learning, testing & getting there a step at a time.

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Soooooo …

Matt, I suggest you get the 315’s all the way around & the front geometry optimized first. Then … you need to either decide what you think is the best spring & ARB package for you & bolt it on … or pick a baseline spring & ARB package to start with … go run it, test & tune on it … until you get it dialed in for your goals. Some guys want to get it done & just drive it. Other guys want to tinker & improve. I feel the decision is a personal one, depending on your priorities, goals & desires.

If you go the test & tune route … as a baseline to tune from … I’m sticking with my recommendation of
Front Springs: 450# … depending on the motion ratio.
Front Sway Bar: 447#
Rear Springs: 250#
Rear Sway Bar: 344#
* After learning his car's front motion ratio, I upped the suggestion to 550# front springs.

I think it will need a bigger front ARB … substantially bigger … and then this baby will turn well & carry good corner speed. But I think you need to get the 315’s on & the geometry right ... with this set up ... and feel how the car handles.

It isn’t going to plow under like it did before. I’ll bet you 3 beers & a hamburger. :cheers:

[Ron Sutton]

Part 3 of Matt's questions & my answers ...

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p.s. your discussion with Jason brought up another question I started to ponder? From my experience, it doesn't seem possible to lift the inside rear tire of our types of cars on a turn.

The goal is NOT to lift it off the ground, just to reduce the load & grip of the inside tire a bit on corner entry & middle. I think Jason mentioned that first & I was just responding to his questions & comments, of which he was spot on. No doubt ... IF you have enough traction & body roll combined … you can make either inside tire come off the ground.

Here are some photos.


77975

77976

77977


The common denominators are …
1. Tight radius corner.
2. Soft springs & high CG for excessive body Roll Angle
3. Enough tire grip for the weight of the car. (It’s easier with light cars, like the ones in the photos, because they don’t require as much tire.)

Reminder: The goal is NOT to lift it off the ground, just to unload it a bit on corner entry & middle, for better turning.

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I'm guessing the roll center would have to be astronomically low compared to the center of gravity, and even then I would think that a car with a roll center that low would need a really stiff spring to compensate.
No, just a high CG, soft suspension & enough grip.

This got me thinking about your opinion on roll centers. I frequently ask Mike Maier, who is a friend of mine, various tuning questions, and he is always of the opinion that lowering the roll center helps provide more rear "bite" to a car. He does run a very stiff rear spring but the car works very well for autocross.
Yes, Mike is right … but he doesn’t need me to say that. Mike is a very smart chassis guy & tuner. We’re friends too, talk often and are the same page. He & I agree on low rear roll centers on short tracks & yes, our rear spring & ARB packages make it work.

By lowing the roll center, even if stiffer springs are used to limit the degree of body roll, would the car be transferring its weight much quicker.
You're correct, but I to state it differently, just to be technically correct, to: It rolls very little … so it’s not transferring the weight very far … planting the tire quicker. Make sense?

That would be ideal for autocross, but less so for a car that sees big road course track time. In your opinion is there another way of achieving similar results without quite as much compromise? I suppose you are always going to compromise somewhere.

Thanks, Matt

For road racing, or any high speed driving … you simply raise the roll centers. The spring package can the same … still soft in front & stiff in the rear … and work well. Of course if you want to optimize the performance for each track ... you're going to tune to that track, so springs can change. But if you want one set-up to drive & not change the springs, it will work.

But again, for optimum handling you raise both roll centers on faster tracks with higher speed corners & lower the roll centers on lower speed, tighter tracks. Remember, it’s not about eliminating Roll Angle. It’s about achieving the correct Roll Angle for the corners you’re running.


Reminder from the 20 Concepts I shared with you earlier:

13. Optimum roll angle works & loads both sides of the car’s tires “closer to even” ... within the optimum tire heat range … providing a consistent "long run set-up" & optimum cornering traction throughout a multi-lap event. Long run set-ups typically take ½ a lap to a whole lap for the tires to “come in” 100%. (Road Course)

14. Higher roll angles work better in tight corners but suffer in high speed corners. Lower roll angles work better in high speed corners but suffer in tight corners. The goal on a road course with various tight & high speed corners … is to find the best balance & compromise that produces the quickest lap times.

15. Too much roll angle overworks the outside tires in corners & underworks the inside tires. Too little roll angle underworks the outside tires in a corner. Excessive roll angle works the outside tires too much … may provide an “ok” short run set-up … but will be “knife edgy” to drive on long runs. The tires heat up quicker & go away quicker. If it has way too much roll angle … the car loses grip as the inside tires are not being utilized.

18. The car’s Center of Gravity acts as a lever on the Roll Center … separately front & rear. Higher CG’s and/or lower RC’s increases roll angle. Lower CG’s and/or higher RC’s decrease roll angle. Getting the front & rear of the car to roll similar is desired. Getting them to roll the same is not, because …

19. Goal: To have optimum grip on all tires and disengage the inside rear tire (to a degree) to turn well … then re-engage the inside rear tire (to a higher degree) for maximum forward bite on exit. So, on entry & mid-corner, the car needs to roll less in the front to keep both front tires engaged for optimum front end grip, while allowing the car to roll slightly more in the rear to disengage the inside rear tire, to a small degree, to turn better. For optimal exit, the car will have more roll in the front & less in the rear to re-engage the inside rear tire to a higher degree than it was on entry & exit, for maximum forward bite (traction) on exit.

[Cobra 498]

Hi Ron,
Appreciate the perspective here. I wonder if maybe our apparent disagreement isn't really a difference over the underlying principles, but maybe just the way we talk about them.

Using your scales approach from above, let's take a hypothetical "totally symmetrical car" - everything is the same about it any way you cut it in half. 50/50 weight distribution with its CG at vehicle centerline along the longitudinal or lateral axes.

Let's say at rest this car looks like this on the scales:
{At rest baseline}
LF 500# RF 500#
LR 500# RR 500#
Left side total: 1000#
Right side total: 1000#
Front total: 1000#
Rear total: 1000#


Now let's say we did something to simulate a cornering situation - maybe we attach a cord to the CG, and pull directly horizontal with some force F. Our tires stay stuck to the scales, but that force rolls the car just as it would in a corner, and based on this car's setup, now our scales read:
{Cornering force F baseline}
LF 750# RF 250#
LR 750# RR 250#
Left side total: 1500#
Right side total: 500#
Front total: 1000#
Rear total: 1000#

Now, we do something to stiffen the front swaybar some amount. But we did so without adding weight or changing anything else about the car. At rest, it still looks the same:
{At rest stiffer front bar}
LF 500# RF 500#
LR 500# RR 500#
Left side total: 1000#
Right side total: 1000#
Front total: 1000#
Rear total: 1000#

The difference, is now what happens when we apply the exact same lateral force F, now that we have increased the front roll stiffness?

I contend we will see something like this:
{Cornering force F stiffer front bar}
LF 750+X# RF 250-X#
LR 750-X# RR 250+X#
Left side total: 1500#
Right side total: 500#
Front total: 1000#
Rear total: 1000#

I contend we haven't changed the total resulting total load on either the left side or right side tires from baseline, even though the car might visually be leaned less now in response to the same lateral force F (e.g. we haven't reduced the total amount of weight transfer). Whatever additional weight transfer X occurred on the front axle, will be the amount of reduced weight transfer we see on the rear axle.

When I read "Stiffer bars reduce roll angle, engaging the inside tires more." What I hear is one of the classic misconceptions in vehicle handling (which seems out of place amongst your otherwise correct information) - that quantity of roll is directly related to quantity of weight transfer, and the more roll, the more weight transfer independent of lateral acceleration. A corollary misconception is that which says the car that squats more, has more rearward weight transfer. I think the basis of this misconception is that when you see two cars with identical setups, and one is rolling more, then there is more weight transfer - but only because that car is cornering harder (more torque about the CG).

If stiffening the front bar resulted in more weight on the inside wheels at the same lateral force F, where is that load coming from? Since our car can't magically gain weight, it has to come from reduced load on the outside tires. This all means a reduction in front-view torque about the CG, and there is no other force available to counteract the torque presented by the cord tugging at the CG. It doesn't add up.

What does make sense is "Stiffer bars reduce roll angle, engaging the inside tire on the other axle more (but not the "inside tires" as a whole)" - if you can live with that interpretation, then maybe we can find some agreement. :)

Jason is on the money with regard to weight transfer vs CG height and track width, I was wondering if anybody would bring that up while browsing through this very interesting thread.
I may have missed it but steering Akerman can be a cause of understeer on slow speed tight radius corners especially on new tire designs with very short sidewalls.

[Ron Sutton]

This post topic moved to another thread here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas).

[diesel25lrs]

:seizure: WOW....:worship:

Really looking forward to the P.S.!

[j-rho]

Moved here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas) for Matt's sake

[Ron Sutton]

This post topic moved to another thread here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas).

[RobNoLimit]

Hey Ron, just have to say thanks for all the great info here. You have got me thinking. I don't want to jack Matts thread, because i'm really interested in his car, and how he can prep for Optima. After Columbus I'll start a new thread, or we'll put a new discussion on the HellBoy build thread.
1). Track/Tread width. the truck was built with the idea that a wider stance is better. and with the wide-5 hardware it's really easy to change it. For the last year or so I have had the tread width at 73" ft and 71" rr. I have always had a push going in and in the middle, corner exit is good. If it gets away from me, i have to wait in the turn until it calms down and then exit the corner. I have used a bit of rear steer set up in the rear bars to combat this. After reading (several times) and digesting the track/tread width info, I'm seeing the flaw in my set up. or at least one of them. So I made a changeand got the widths to 73/72.6 - it runs a 315 all the way around.
2). KPI split. First off, thanks for saying a number (static caster = KPI + 1, or so) I have always been a big believer in caster, but in the hot rod/street rod/truckin worlds, I think I'm alone. I have studied many late model cars, BMW, Mercedes, vette, even the chrysler 300, and they have BIG caster numbers. I have been running in the 6 to 8 range, and although thought I needed more, but my initial UCA fabbed components stopped me. The HOWE spindles are 9 degree (I say KPI, just used to it) so over the weekend I fabbed some new ball joint sockets and longer front legs and was able to get an adjustment range from 6 to 12 deg. Currently set at 10 (KPI + 1), This did create some bumpsteer, but this is really easy for me to fix, the rack mount 'z' axis is slotted, and the lower steering shaft has a slip shaft.
3). I use AutoWare Suspension Geometry Pro, it's simple to use. and I'm quick enough at it to use it in the shop during fab and set ups. Thats makes things go a lot faster. Some other info. The truck weighs 3285 with me in it. 53.7% ft. The truck has always felt tight in the rear, so I calced the total roll resistance ft/rr, and guess what, yep, the rear was higher (based on wt %) than the front. So, I went back to the 200 springs that I ran last year. - and now think that 175 may be a better choice.
I have no time to track test before I leave for Des-Moines and Columbus, but I did go over to the CHP training lot here in San Bernardino (hey, there weren't using it) saturday afternoon and I am very happy with the fell and results. Skip pad l/r produced better tire temps and better times than ever before (I use 'trackmaster' phone app) slolom times also went from a best of 48.3 mph to a new best of 49.7. - and the tires look better. BTW, it was 112 degrees out.
So, wish me luck, I'm off on a road trip, got lots of spare parts, a laptop, i-pad and three clip boards of notes. Thanks for sharing the info. Watch our facebook - No Limit Engineering, i'll keep you posted.

[Ron Sutton]

Hey Ron, just have to say thanks for all the great info here. You have got me thinking. I don't want to jack Matts thread, because i'm really interested in his car, and how he can prep for Optima. After Columbus I'll start a new thread, or we'll put a new discussion on the HellBoy build thread.
1). Track/Tread width. the truck was built with the idea that a wider stance is better. and with the wide-5 hardware it's really easy to change it. For the last year or so I have had the tread width at 73" ft and 71" rr. I have always had a push going in and in the middle, corner exit is good. If it gets away from me, i have to wait in the turn until it calms down and then exit the corner. I have used a bit of rear steer set up in the rear bars to combat this. After reading (several times) and digesting the track/tread width info, I'm seeing the flaw in my set up. or at least one of them. So I made a changeand got the widths to 73/72.6 - it runs a 315 all the way around.
2). KPI split. First off, thanks for saying a number (static caster = KPI + 1, or so) I have always been a big believer in caster, but in the hot rod/street rod/truckin worlds, I think I'm alone. I have studied many late model cars, BMW, Mercedes, vette, even the chrysler 300, and they have BIG caster numbers. I have been running in the 6 to 8 range, and although thought I needed more, but my initial UCA fabbed components stopped me. The HOWE spindles are 9 degree (I say KPI, just used to it) so over the weekend I fabbed some new ball joint sockets and longer front legs and was able to get an adjustment range from 6 to 12 deg. Currently set at 10 (KPI + 1), This did create some bumpsteer, but this is really easy for me to fix, the rack mount 'z' axis is slotted, and the lower steering shaft has a slip shaft.
3). I use AutoWare Suspension Geometry Pro, it's simple to use. and I'm quick enough at it to use it in the shop during fab and set ups. Thats makes things go a lot faster. Some other info. The truck weighs 3285 with me in it. 53.7% ft. The truck has always felt tight in the rear, so I calced the total roll resistance ft/rr, and guess what, yep, the rear was higher (based on wt %) than the front. So, I went back to the 200 springs that I ran last year. - and now think that 175 may be a better choice.
I have no time to track test before I leave for Des-Moines and Columbus, but I did go over to the CHP training lot here in San Bernardino (hey, there weren't using it) saturday afternoon and I am very happy with the fell and results. Skip pad l/r produced better tire temps and better times than ever before (I use 'trackmaster' phone app) slolom times also went from a best of 48.3 mph to a new best of 49.7. - and the tires look better. BTW, it was 112 degrees out.
So, wish me luck, I'm off on a road trip, got lots of spare parts, a laptop, i-pad and three clip boards of notes. Thanks for sharing the info. Watch our facebook - No Limit Engineering, i'll keep you posted.



Hey Rob, thanks for the shout out.

When you get back, let's start a new thread & discuss what effects the changes had, so everyone can learn, chime in & ask questions.

Glad to hear the changes improved your skid pad numbers. 1.4 mph is pretty big.

Good luck in Des-Moines and Columbus.

[Ron Sutton]

Matt,

I suggest you figure out what your scrub radius with your current set-up ... and then with your new set-up. I "think" you're going to make it much smaller & better ... and that will help your turning also. It will be good for you & everyone reading along to see what the change was.

As you know, I measure everything & work it out in a suspension software. But for the average guy in his garage ... do this:

a. Determine the EXACT centerline height of your front spindle (Pick one ... left or right ... doesn't matter) ... with all 4 wheels & tires on the ground ... suspension loaded. It is going to be around 12-13". Let's say it is 12-3/4".

b. Remove that tire & wheel. Put a good, non-leaking jack under the the ball joint (or other secure point on the lower A-arm) & jack the spindle back to that exact same height ... in this example 12-3/4". (you are simulating ride height ... with 3 tires on the ground & a jack under one front corner.

c. Using a string, laser, straight edges or whatever works for you ... make a true line through the CENTERS of the upper & lower ball joints ... projecting onto the floor. Mark it. (I use blue 3M masking tape, so I'm not marking up my floor permanently.)

d. Ideally ... you want the mark on the shop floor to be more than a dot. What works best is a line 8-12" long TRULY PARALLEL with the car.

e. Put your tire & wheel back on ... and set the car on the ground.

f. Find the true centerline of your tire tread ... and measure the distance to the line you put on the floor. Whatever that measurement is ... in inches ... is your scrub radius. This method may not be dead on accurate ... but it'll be close enough to know what you're working with.


79171


Please post your Scrub Radius dimension, so I also know what we're working with.

[Rod]

Hey Ron, just have to say thanks for all the great info here. You have got me thinking. I don't want to jack Matts thread, because i'm really interested in his car, and how he can prep for Optima. After Columbus I'll start a new thread, or we'll put a new discussion on the HellBoy build thread.
1). Track/Tread width. the truck was built with the idea that a wider stance is better. and with the wide-5 hardware it's really easy to change it. For the last year or so I have had the tread width at 73" ft and 71" rr. I have always had a push going in and in the middle, corner exit is good. If it gets away from me, i have to wait in the turn until it calms down and then exit the corner. I have used a bit of rear steer set up in the rear bars to combat this. After reading (several times) and digesting the track/tread width info, I'm seeing the flaw in my set up. or at least one of them. So I made a changeand got the widths to 73/72.6 - it runs a 315 all the way around.
2). KPI split. First off, thanks for saying a number (static caster = KPI + 1, or so) I have always been a big believer in caster, but in the hot rod/street rod/truckin worlds, I think I'm alone. I have studied many late model cars, BMW, Mercedes, vette, even the chrysler 300, and they have BIG caster numbers. I have been running in the 6 to 8 range, and although thought I needed more, but my initial UCA fabbed components stopped me. The HOWE spindles are 9 degree (I say KPI, just used to it) so over the weekend I fabbed some new ball joint sockets and longer front legs and was able to get an adjustment range from 6 to 12 deg. Currently set at 10 (KPI + 1), This did create some bumpsteer, but this is really easy for me to fix, the rack mount 'z' axis is slotted, and the lower steering shaft has a slip shaft.
3). I use AutoWare Suspension Geometry Pro, it's simple to use. and I'm quick enough at it to use it in the shop during fab and set ups. Thats makes things go a lot faster. Some other info. The truck weighs 3285 with me in it. 53.7% ft. The truck has always felt tight in the rear, so I calced the total roll resistance ft/rr, and guess what, yep, the rear was higher (based on wt %) than the front. So, I went back to the 200 springs that I ran last year. - and now think that 175 may be a better choice.
I have no time to track test before I leave for Des-Moines and Columbus, but I did go over to the CHP training lot here in San Bernardino (hey, there weren't using it) saturday afternoon and I am very happy with the fell and results. Skip pad l/r produced better tire temps and better times than ever before (I use 'trackmaster' phone app) slolom times also went from a best of 48.3 mph to a new best of 49.7. - and the tires look better. BTW, it was 112 degrees out.
So, wish me luck, I'm off on a road trip, got lots of spare parts, a laptop, i-pad and three clip boards of notes. Thanks for sharing the info. Watch our facebook - No Limit Engineering, i'll keep you posted.

That will be a fun one I'm in on that

[mitch_04]

This needs to be a sticky of some sort. I had to stop reading halfway through page 3 because I can only digest so much at a time, but wow!!! This is as good as any book I have read so far, maybe I'm reading the wrong books...

[Ron Sutton]

Hi Mitch,

Thanks for the Kudos. Hang with us as Matt & I are going to do some cool stuff over the next month.

A few other good threads I'm involved in are:

Lance's Monte Carlo (https://www.pro-touring.com/showthread.php?98063-Need-a-little-help-figuring-something-out) I join in at post #24, but read it from the start & watch the videos of the tires.

Josh's Camaro (https://www.pro-touring.com/showthread.php?99921-Suspension-questions-for-69-camaro)

[j-rho]

Moved here (https://www.pro-touring.com/showthread.php?100142-When-the-Results-Don-t-Match-The-Principals-or-Formulas) for Matt's sake

[Bryce]

great info.

I was just giving my suspension some thought last night and saw this thread today, so good timing. I can adjust every aspect of my suspension so trying to decide if I have short comings. I lose 1 degree of camber at max steering input (not too bad) so some more caster will help that.

Thanks for taking your time to post all of this!

[Ron Sutton]

Hey Guys,

I'm on the Forum today for a few more hours ... then I'll be gone for a week.


I'm meeting up with my friend Neil Porter at Sears Point where he's running 2 formula cars in SCCA racing.

https://www.pro-touring.com/attachment.php?attachmentid=78694&d=1373072350



Then I'm camping with my girls the rest of the week.

https://www.pro-touring.com/attachment.php?attachmentid=78695&d=1373072681



I'll be back online late Thursday (7/11) or Friday morning (7/18).

[iadr]

https://static1.pt-content.com/images/pt/2013/06/cuuuda5_zps5b8b108b-1.jpg (http://s1357.photobucket.com/user/tomswheels/media/Barracuda/cuuuda5_zps5b8b108b.jpg.html)

No comment needed, however, note the front left wheel / rear bumper angle. Almost perfect! :thankyou:

I've been mulling this over two different nights, and decided to "call" the poster and his friend on this:

It the above sarcasm? Obviously you want the left front wheel not to look anything like it does. You want it to have the same relation to vertical as the left rear wheel does in that photo. The only excuse to have your left front wheel looking like that is it is a compromise when you desperately need the outer (right front) to do something that can't be achieved with your hardware any other way.

Lets talk this out.

[72BBSwinger]

The times that car lays down with the parts it has speak for them selves....

[Tomswheels]

Yes, Sarcasm.... I like to give this posts original author (Matt and his 69 Camaro) a hard time because that was the one event I got extremely lucky and beat him at (at least on Sat). You think the front wheels looks less than ideal, you should feel it from the drivers seat-- Scary!! On a non-sarcastic note though, as Ron stated sometimes a bit of roll can result in some decent lap times. I initially took too much lean out of this car, and after many laps with a rear sway bar, I learned this Barracuda is faster at Autocross w/o it...

[Ron Sutton]

Hey Guys,

A reminder from Post #81 of this thread

Roll Angle vs Pitch angle: A handling car can’t run flat … it needs to travel … so it’s either got to Roll or Pitch … that’s the primary difference in the two tuning concepts.

• It can’t pitch a lot AND roll a LOT … it would be dangerous & undrivable
• It can’t pitch AND roll a LITTLE … it would just skate on the road surface.
• It can pitch a lot & roll a little … OR it pitch a little & roll a lot

You need to pick a path … so here is what they look like.

-------------------------------------------------------------------------------------------------------

Conventional:
• Stiff front springs
• Small, soft sway bars
• More Roll
• Less Pitch

Old School – Let it Roll
• Moderate to High Roll Angle (3 to 6 degrees)
• Front suspension doesn’t compress much on entry. (3/4” to 1-1/2”)
• Load the outside tires for grip & unload the inside tires so it will turn.

Drawbacks:
• Too much roll angle overworks the outside tires in corners & underworks the inside tires.
• The tires heat up quicker & go away quicker, providing a better short run set-up. (AutoX !)
• After tires “come in” the car is “knife edgy” to drive.
• Very line sensitive … drivers say, “can’t drive it just anywhere” … meaning it handles poorly out of its optimum groove.
• As the track grip increases & the car rolls more … these problems magnify.
• When it rolls a lot & you brake hard, the inside rear tire has no grip. So to prevent from being loose on entry you must run stiffer front springs.
• The stiffer front springs make the car tight/pushy in the middle … requiring the driver to brake more and run slower corner speeds.


-------------------------------------------------------------------------------------------------------

High Travel:
• Soft front springs
• Big, stiff sway bar in front
• Known as SS/BB … soft spring/big bar … if no bump stop or coil bind is utilized.
• Same concept used in conjunction with travel stops: Bump Stops or Coil Bind
• Less Roll
• More Pitch

New School – Get the nose on the ground & run the car flatter
• Roll angle is minimal, controlled primarily by the sway bar in front & stiffer rear suspension. (1 to 1.75 degrees)
• Front suspension travels a LOT in dive (compress) to put maximum load & grip on front tires. (3” +)
• Load the outside tires only slightly more than inside corners for optimum 4 tire corner grip.

Disadvantages:
• Even when optimized … it still can not be driven as deep on corner entry as a conventional set up.
• When racing door-to-door in a field of race cars running a mixture of set-ups, the SS/BB set-up is susceptible to dive bomb passes.

Advantages:
• Flatter Roll Angle works the tires more evenly.
• The tires heat up slower & last longer … making a better long run set-up as the tires are “good” way longer. (Road Race)
• Less line sensitive … drivers say, “I can drive it just anywhere” … meaning any line on the track.
• As the track grip increases … the advantages show more.
• The soft spring/high travel front end puts creates maximum grip on front tires for highest cornering speeds.
• Will produce faster cornering speeds & quicker lap times over conventional set-up, all other things being equal.


-------------------------------------------------------------------------------------------------------

In the top professional racing series, everyone is on the newer higher travel/low roll set-ups. But in lower sportsman levels, there are many series where the competitors run both, and some series where they all run low travel/ high roll.

In a field of cars with different people competing with these two styles of set-ups, things are rarely equal. But when two theoretical "identical" cars are ran with the two set-ups ... and those set-ups are fully optimized ... the high travel/low roll angle set-up will be faster, but not by a ton.

And if on any given day the the low travel/high roll team is "spot on" ... they can & do win ... and when the team on the newer high travel/low roll set-up is "off" their set-up a bit they can & do lose just as easily. To paraphrase comedian Ron White says, "I know, I've seen me do it." :twothumbs

.

[Ron Sutton]

Hey Tom,

When you removed the rear sway bar, what changed in your handling specifically ?

[Tomswheels]

With sway bar on the car was always oversteering. Rear broke away early and often. Taking it off made the car lean more, but stick better.

[Ron Sutton]

With sway bar on the car was always oversteering. Rear broke away early and often. Taking it off made the car lean more, but stick better.

Thanks. That's the normal affect for a stock suspended car.

[iadr]

I just wanted to say (aside from sorry if I came off rude with Tom's car- they say sarcasm is lost on the autistic. Certainly, if there's a spectrum, I'm over on that end... :( ) that I found the explanation of why SAI stuffs the outside tire into the pavement, one of the few things Ron sort of glossed over. I'd thought about it for what a couple weeks now? And didn't "get it" until an hour ago.
Figure 5 here: (I didn't even need to get to 6-10, I had my a-ha! moment before I scrolled):
http://www.ismasupers.com/downloads/tech-talk/Tech-02%20Suspension%20Geometry%20relations%204.pdf
The spindle's snout (being a traditional spindle illustrated, not a bolt on hub type) being at an angle is really what "does it", or rather, that, as the complete knuckle rotates the "theoretical" 90 deg, the SAI goes from its true angle to being, as viewed from the side, vertical. And the snout's previously "appropriate" built-in angle..., well, you wish it would go away. lol
This is harder to explain than I thought.

Anyway, I was wondering if Ron you felt like commenting on: if a close to Zero SAI spindle would be ideal for street/Autocross. Or why you wouldn't want that. ??? I have an interesting project on a non-protouring vehicle, which is to adapt Lexus IS-AWD front spindles and upper arms in place of a macpherson strut. The parts are one of those tall spindles with the "hook" at the top putting the upper BJ overtop the inner tread blocks of the tires. Just a conventional 10.5* SAI, but it looks like they could have gone further out with the upper BJ and reduced the SAI if they wanted too. They compete with the German cars that use two separate upper BJ's to (at least to my eyes) put the effective upper BJ location well out over the tire. Are you familiar with what I mean? Theoretically, you could do a conventional lower BJ, and one of those up top to have Zero SAI. Would your steering feel be poor? (not that it's that great on the last few year's car's anyway... you get on local snowy roads here in Canada with a car with 40-series tires and a 10:1 steering ratio+electric boost, and little body roll, and you have zero progessiveness, or ability to finesse-catch it...because the reactions are all moved up to high G points. Back in the day street cars gave feedback at like .15-.2G. Not anymore.)
I gather of bits of the puzzle from places as disparate as Edmunds Suspension walk arounds, and the Locost Lotus seven replica building community.
On the former, here are a couple interesting ones:
http://www.edmunds.com/car-reviews/track-tests/2009-audi-s5-suspension-walkaround.html
http://www.edmunds.com/car-reviews/track-tests/2012-bmw-328i-suspension-walkaround.html
The second has an animated .GIF picturing the one thing I mentioned.

[iadr]

Hmm, watching the BMW .gif, I think I need help understanding what is going on. It is not as simple as moving out the pivot point, because at higher angles the pivot tucks *inside*. Hmm.

(???)

[Ron Sutton]

I just wanted to say (aside from sorry if I came off rude with Tom's car- they say sarcasm is lost on the autistic. Certainly, if there's a spectrum, I'm over on that end... :( ) that I found the explanation of why SAI stuffs the outside tire into the pavement, one of the few things Ron sort of glossed over. I'd thought about it for what a couple weeks now? And didn't "get it" until an hour ago.
Figure 5 here: (I didn't even need to get to 6-10, I had my a-ha! moment before I scrolled):
http://www.ismasupers.com/downloads/tech-talk/Tech-02%20Suspension%20Geometry%20relations%204.pdf
The spindle's snout (being a traditional spindle illustrated, not a bolt on hub type) being at an angle is really what "does it", or rather, that, as the complete knuckle rotates the "theoretical" 90 deg, the SAI goes from its true angle to being, as viewed from the side, vertical. And the snout's previously "appropriate" built-in angle..., well, you wish it would go away. lol
This is harder to explain than I thought.

Anyway, I was wondering if Ron you felt like commenting on: if a close to Zero SAI spindle would be ideal for street/Autocross. Or why you wouldn't want that. ??? I have an interesting project on a non-protouring vehicle, which is to adapt Lexus IS-AWD front spindles and upper arms in place of a macpherson strut. The parts are one of those tall spindles with the "hook" at the top putting the upper BJ overtop the inner tread blocks of the tires. Just a conventional 10.5* SAI, but it looks like they could have gone further out with the upper BJ and reduced the SAI if they wanted too. They compete with the German cars that use two separate upper BJ's to (at least to my eyes) put the effective upper BJ location well out over the tire. Are you familiar with what I mean? Theoretically, you could do a conventional lower BJ, and one of those up top to have Zero SAI. Would your steering feel be poor? (not that it's that great on the last few year's car's anyway... you get on local snowy roads here in Canada with a car with 40-series tires and a 10:1 steering ratio+electric boost, and little body roll, and you have zero progessiveness, or ability to finesse-catch it...because the reactions are all moved up to high G points. Back in the day street cars gave feedback at like .15-.2G. Not anymore.)
I gather of bits of the puzzle from places as disparate as Edmunds Suspension walk arounds, and the Locost Lotus seven replica building community.
On the former, here are a couple interesting ones:
http://www.edmunds.com/car-reviews/track-tests/2009-audi-s5-suspension-walkaround.html
http://www.edmunds.com/car-reviews/track-tests/2012-bmw-328i-suspension-walkaround.html
The second has an animated .GIF picturing the one thing I mentioned.

When I'm designing a race car with no rules limiting me on spindles or control arms ... I am using custom built spindles with very low KPI/SAI ... long control arms pushing the ball joint out & deep back spaced wheels ... to arrive at zero scrub radius. You don't need any more KPI angle than necessary to achieve a zero scrub radius.

I personally have no experience with a zero KPI spindle, and could not tell you if there are any issues. I have no experience going that low, because I haven't been in a situation where zero KPI would get me zero scrub radius. Zero scrub radius is the primary goal.

I have several projects where we achieved zero scrub radius with 3 degree & 5 degree KPI spindles. As long as we can achieve a zero scrub radius set-up ... and the caster can be adjusted 1-2 degrees more than KPI ... one isn't necessarily better than the other.

[Ron Sutton]

Hmm, watching the BMW .gif, I think I need help understanding what is going on. It is not as simple as moving out the pivot point, because at higher angles the pivot tucks *inside*. Hmm.

(???)

I did not understand this message. Is there a BMW.gif on this thread? If yes, in what post?

[Norm Peterson]

It's not in any post here.

Look about a quarter of the way down the BMW suspension walkaround link http://www.edmunds.com/car-reviews/track-tests/2012-bmw-328i-suspension-walkaround.html for a picture that animates automatically.


Norm

[Ron Sutton]

It's not in any post here.

Look about a quarter of the way down the BMW suspension walkaround link http://www.edmunds.com/car-reviews/track-tests/2012-bmw-328i-suspension-walkaround.html for a picture that animates automatically.

Norm

Thanks Norm. That's pretty cool.

Iadr, I couldn't speak intelligently on the BMW suspension that has a dynamic scrub radius, as I have no experience with it. But it's looks neat.

.