Let's talk anti-roll bars

[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.

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.

[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.









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.

[diesel25lrs]

WOW....

Really looking forward to the P.S.!

[j-rho]

Moved here for Matt's sake

[Ron Sutton]

This post topic moved to another thread here.

[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.





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 I join in at post #24, but read it from the start & watch the videos of the tires.

Josh's Camaro

[j-rho]

Moved here 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.





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





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

[iadr]

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

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."

.