Let's talk anti-roll bars

[Rod]

ha ha ha ha 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?

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?
Of Course !!!

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.

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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.




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.


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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.

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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.

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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.





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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.

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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.

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-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.

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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.

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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.

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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.

[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 for Matt's sake