Trying to cure understeer

[cliffordm4]

My current setup:
Ohlins R&T, 90N/m and 230N/m springs
SPL thrust arms
SPL FLCAs
SPL sway bar links
SPL rear toe arms
SPL rear trailing arms
Ground Control camber plates

I don't have the exact alignment specs, but it's decently aggressive. 0 front toe, -3.x front camber, -2.5ish rear camber.

At Laguna over the summer on 265/325 AR1s, I had some pretty bad understeer. I don't remember exactly what settings I had on the Ohlins at the time.

I recently did a wet track day on 275/315 PS4S, but wasn't pushing hard enough to notice the understeer.

Would I benefit from a stiffer swaybar (M2 CSR comes to mind) to combat the understeer I was experiencing at Laguna? Going to be running 265/305 CR-S this summer season, if that makes a difference.

What settings should I try on the Ohlins to help with the understeer and overall performance on track?

Thank you all

[RugbyBro]

You’re running a pretty massive stagger with your tires, try reducing the stagger or better yet, run square. I.e you need more front tire or less rear tire.

[cliffordm4]

Originally Posted by RugbyBro

You’re running a pretty massive stagger with your tires, try reducing the stagger or better yet, run square. I.e you need more front tire or less rear tire.

Yeah, at the time it was the only sizes available - not ideal, I know. The 265/305 stagger should be better, but I'm just curious if it has to do with suspension too. I hear the Ohlins are prone to understeer, I'm just curious how to fix it

As to running square, I currently have 19x10 fronts and 19x11 rears. Wouldn't it not be ideal to run square on those rims? Not super stoked about having to go down in size on the rears - I'm limited on space up front. The 275/35 is pretty much the limit of what fits up there.

[RugbyBro]

Originally Posted by cliffordm4

Yeah, at the time it was the only sizes available - not ideal, I know. The 265/305 stagger should be better, but I'm just curious if it has to do with suspension too. I hear the Ohlins are prone to understeer, I'm just curious how to fix it

As to running square, I currently have 19x10 fronts and 19x11 rears. Wouldn't it not be ideal to run square on those rims? Not super stoked about having to go down in size on the rears - I'm limited on space up front. The 275/35 is pretty much the limit of what fits up there.

Yes to run square you ideally want 4 of the same wheel, doesn’t make sense to run it on a staggered wheel setup. You are correct that the 265/305 will be less understeery than your previous setup, but you’ll still run into understeer. I think in this case it’s more of a tire issue but you can adjust for it by either softening the front damping or stiffening the rear damping or both- you’ll have to play with it a bit to find the right balance of adjustments.

Edit: sounds like you already have the tires? Just make the most of them and make some suspension adjustments mentioned above. You can run sway bars however you would really need a rear sway, not a front. A front sway will just further stiffen the front and induce more understeer.

[M3SQRD]

Originally Posted by cliffordm4

Yeah, at the time it was the only sizes available - not ideal, I know. The 265/305 stagger should be better, but I'm just curious if it has to do with suspension too. I hear the Ohlins are prone to understeer, I'm just curious how to fix it

As to running square, I currently have 19x10 fronts and 19x11 rears. Wouldn't it not be ideal to run square on those rims? Not super stoked about having to go down in size on the rears - I'm limited on space up front. The 275/35 is pretty much the limit of what fits up there.

Depending on how you’ve setup the car, a staggered setup can work just as well as, or better than, a square setup. I run front 285/295 and rear 305 setup and I have no issues with understeer, plus I can better put the power down sooner on corner exit (started running a GTS tune in 2019 on my ‘16 M4). Disadvantage to a staggered setup is not being able to swap tires front-rear and left-right to increase longevity; however, I’ve had good luck with swapping tires left-right only.

You can try to adjust damping front and rear but, unfortunately, you don’t have independent low-speed damping control which controls weight transfer and to a certain degree steady-state cornering (damping is zero at true steady state cornering because damping is related to piston velocity which is zero at steady state). You’ll completely screw up the damping control over bumps and curbs if you set your dampers up to deal with steady-state understeer. You’re already running quite high rear spring rates so I wouldn’t recommend increasing the rear rate. It would really help to know where you had the dampers set when you experienced understeer because you can easily overdamp the springs, in particular the front springs, with R&T stock valving. When’s the last time you adjusted the damping? Could it be the same settings used at LS?

[FaRKle!]

I agree with others that your understeer is related to having too big of a tire stagger due to the native Ohlins spring rates. Even with the stiffer 230N/mm rear spring you'd still want to run more towards square.

Adding a stiffer front bar will only make things worse than they are right now if you're understeering.

There's no issue running square tires on stagger wheels. You just still won't have the benefit of rotating them, but will have the handling benefits. I did that (ran 265 square on 9.5/10.5 wheels) to test how a square setup would feel.

For the GT4 aero you're considering, I'd try it with the existing springs first, and then decide if you need a change. I don't really think you'll need to change though, and you probably shouldn't go stiffer than the existing 230N/mm spring in the rear since it won't be within working range (it'd be more ideal going to coilover rear and using lower spring rates to achieve a higher rear wheel rate).

[OG Shark]

With the limited control over a single adjustment suspension you are really dependent on their valving for handling characteristics like that. Like M3SQRD mentioned making adjustments with a single is going to make changes to everything and might induce negative traits somewhere else. You can play with spring rates but also like he mentioned pretty high in the rear already and soft in the front. Sways like RugbyBro mentioned would be more on the rear side too for what you are looking to do but I don't think that is the main culprit.

That tire stagger is huge... A proper staggered setup on the F8x is typically* the fastest way around the track - but that big a delta is a huge cause of understeer. I try to keep it at maximum 20mm. Will push to 30 if the situation dictates it (usually by rule constraints). 40mm is ugh - can still get around fairly quick but just really isn't that much fun. 60mm is just freaking awful. Please turn, please turn, awww crap didn't want to turn. I would work to keep that stagger within 20mm and retest - see how much of a difference that makes before making physical changes to the car. Certainly adjust the damper settings though just would wait on sways or springs or anything like that. And I say typically - the more tire you can stuff in the front the better so if you can get a decent width up front then running square is not out of the question. Keep in mind that you need square is both wheels and tires being equal widths all for corners - running the same width tire on different wheel widths changes the contact patch dimensions.

[cliffordm4]

Thank you OG Shark and FaRKle!. I will give the smaller (20mm) stagger a shot, and leave spring rates alone for now.

My thinking with the sway bar(s) stemmed from feeling front roll with the Ohlins, even at stiffer settings, hence my questions about both the Ohlins settings and the possibility of adding sways.

Is it correct to say that just adding only a front sway bar induce too much understeer, even with a 20mm stagger setup? Like what @RugbyBro mentioned. (p.s. I haven't bought the tires yet - it's just what I had planned on going with, since I had run that setup before with few issues, but admittedly at a much slower pace).

At what settings are the Ohlins working their best on track? What exactly does "critically damped" mean? Just trying to learn more about suspension dynamics and kinematics

The 60mm was a terrible tire setup, but again, it's all that I could get at the time and I had a few days to get sorted before a track day!

Thank you all for the help!

[jbalabas]

Originally Posted by cliffordm4

Thank you OG Shark and FaRKle!. I will give the smaller (20mm) stagger a shot, and leave spring rates alone for now.

My thinking with the sway bar(s) stemmed from feeling front roll with the Ohlins, even at stiffer settings, hence my questions about both the Ohlins settings and the possibility of adding sways.

Is it correct to say that just adding only a front sway bar induce too much understeer, even with a 20mm stagger setup? Like what @RugbyBro mentioned. (p.s. I haven't bought the tires yet - it's just what I had planned on going with, since I had run that setup before with few issues, but admittedly at a much slower pace).

At what settings are the Ohlins working their best on track? What exactly does "critically damped" mean? Just trying to learn more about suspension dynamics and kinematics

The 60mm was a terrible tire setup, but again, it's all that I could get at the time and I had a few days to get sorted before a track day!

Thank you all for the help!

What settings are you running on your R&T?? My base is 5 clicks from full closed and it's still compliant and supple on track. That being said my local track is a year old and super smooth and I'm quick but far from fast.

[RugbyBro]

Originally Posted by cliffordm4

Is it correct to say that just adding only a front sway bar induce too much understeer, even with a 20mm stagger setup? Like what @RugbyBro mentioned. (p.s. I haven't bought the tires yet - it's just what I had planned on going with, since I had run that setup before with few issues, but admittedly at a much slower pace).

Yes that is correct unless the sway bar is softer than the stock sway you are replacing. Grip and response are inverse to each other, making the front stiffer and more "responsive" will sacrifice grip. Ultimately tweaking damping, springs, and sway bars is a give & take process but any additional front end stiffness will certainly make an already understeer-y setup worse.

Honestly give 275/295 a try - you will probably need to adjust your driving style given you are use to that massive stagger. Whatever you feel like you lose by having less rear tire you will certainly gain and more from the additional front end grip. I personally don't feel that this platform requires more than 295 in the rear for the vast majority of drivers (myself included). The front end on this platform feels like it needs more help than the rear (assuming that the rear is adequately tire'd - 275+). Also, FWIW, the fastest F8X laps I know of personally all run square between 275-295 so there is something to be said about minimizing the front/rear stagger.

[M3SQRD]

Originally Posted by cliffordm4

Thank you OG Shark and FaRKle!. I will give the smaller (20mm) stagger a shot, and leave spring rates alone for now.

My thinking with the sway bar(s) stemmed from feeling front roll with the Ohlins, even at stiffer settings, hence my questions about both the Ohlins settings and the possibility of adding sways.

Is it correct to say that just adding only a front sway bar induce too much understeer, even with a 20mm stagger setup? Like what @RugbyBro mentioned. (p.s. I haven't bought the tires yet - it's just what I had planned on going with, since I had run that setup before with few issues, but admittedly at a much slower pace).

At what settings are the Ohlins working their best on track? What exactly does "critically damped" mean? Just trying to learn more about suspension dynamics and kinematics

The 60mm was a terrible tire setup, but again, it's all that I could get at the time and I had a few days to get sorted before a track day!

Thank you all for the help!

You said the widest tire you can run is a 275 on the front and that’s due to the tire contacting the strut/spring? 275/295 will be better than the staggered setups you’ve been running. A stiffer sway bar can potentially help to reduce understeer on a front strut suspension by providing better control of the camber curve (strut suspension lose camber with suspension compression) but if you’re already struggling with understeer it’s probably not a wise addition. Try the 20 mm stagger first and see whether that reduces the understeer.

Critically damped motion is when a suspension oscillation/disturbance is damped out without the motion overshooting its original undisturbed starting position; i.e., it’s the least amount of damping that results in no vibration (see the second figure in the link below and the curve for zeta = 1.0)

https://www.racecompengineering.com/...itical-damping

You typically want the suspension to be underdamped at low, mid and high damper piston speeds (relative to the damper body) for cars without real downforce. As an example, at lower piston speeds the damping will be around 60-80% of critical damping and at higher piston speeds it’ll be around 20-40% of critical damping. If the suspension is overdamped then the suspension will take too long to return to its starting position so if you encounter a second bump your suspension becomes jacked down (unable to absorb the second bump) with a sudden loss of grip. This is why we’re saying adjusting your single-adjustable (SA) dampers (R&T adjusts both rebound and compression together) to address understeer at low piston speeds (initial turn in) will result in too much/too little damping at higher piston speeds (bump midcorner or a bumpy braking zone). You’ll always have a compromised setup with SA dampers because different parts of the track may require different damping settings.

[andrewmr]

Originally Posted by cliffordm4

My current setup:
Ohlins R&T, 90N/m and 230N/m springs
SPL thrust arms
SPL FLCAs
SPL sway bar links
SPL rear toe arms
SPL rear trailing arms
Ground Control camber plates

I don't have the exact alignment specs, but it's decently aggressive. 0 front toe, -3.x front camber, -2.5ish rear camber.

At Laguna over the summer on 265/325 AR1s, I had some pretty bad understeer. I don't remember exactly what settings I had on the Ohlins at the time.

I recently did a wet track day on 275/315 PS4S, but wasn't pushing hard enough to notice the understeer.

Would I benefit from a stiffer swaybar (M2 CSR comes to mind) to combat the understeer I was experiencing at Laguna? Going to be running 265/305 CR-S this summer season, if that makes a difference.

What settings should I try on the Ohlins to help with the understeer and overall performance on track?

Thank you all

To reduce understeer you'll want to go with a softer sway bar in the front, or a firmer sway bar in the rear. Or springs instead of bars.

Where is the car understeering? Entry, apex or exit?

[N1rve]

If you want more over steer, more grip in the front. If you want more under steer, more grip in the rear.

A softer front end will give more over steer and a stiffer rear end will give more understeer. This is in terms of damping and suspension sway bars. So you want to adjust your front coilovers to a softer setting than the rear.

As you have significantly introduced more grip in the rear than the front from the tires...
Stock is 255/275 and you only went up 10mm in the front but went 30mm+ in the rear, you want to have a softer front sway bar.

[Track/S]

Originally Posted by M3SQRD

You said the widest tire you can run is a 275 on the front and that’s due to the tire contacting the strut/spring? 275/295 will be better than the staggered setups you’ve been running. A stiffer sway bar can potentially help to reduce understeer on a front strut suspension by providing better control of the camber curve (strut suspension lose camber with suspension compression) but if you’re already struggling with understeer it’s probably not a wise addition. Try the 20 mm stagger first and see whether that reduces the understeer.

Critically damped motion is when a suspension oscillation/disturbance is damped out without the motion overshooting its original undisturbed starting position; i.e., it’s the least amount of damping that results in no vibration (see the second figure in the link below and the curve for zeta = 1.0)

https://www.racecompengineering.com/...itical-damping

You typically want the suspension to be underdamped at low, mid and high damper piston speeds (relative to the damper body) for cars without real downforce. As an example, at lower piston speeds the damping will be around 60-80% of critical damping and at higher piston speeds it’ll be around 20-40% of critical damping. If the suspension is overdamped then the suspension will take too long to return to its starting position so if you encounter a second bump your suspension becomes jacked down (unable to absorb the second bump) with a sudden loss of grip. This is why we’re saying adjusting your single-adjustable (SA) dampers (R&T adjusts both rebound and compression together) to address understeer at low piston speeds (initial turn in) will result in too much/too little damping at higher piston speeds (bump midcorner or a bumpy braking zone). You’ll always have a compromised setup with SA dampers because different parts of the track may require different damping settings.

I found this MOTON article where they say that to combat understeer, stiffen the rebound at the front, I'm trying to combat understeer on my m2c with 285/30/18 square (Before with 285/35 tires I had no problems) my GTS turns much better with 275F/285R.

[M3SQRD]

Originally Posted by Track/S

I found this MOTON article where they say that to combat understeer, stiffen the rebound at the front, I'm trying to combat understeer on my m2c with 285/30/18 square (Before with 285/35 tires I had no problems) my GTS turns much better with 275F/285R.

Are you experiencing understeer at initial turn-in only or understeer at corner entry and/or midcorner and/or corner exit with throttle? What are your spring rates and ride heights (i.e., how much forward rake are you running)? I measure rake by measuring the ride height right in front of the forward jack points and the ride height just right behind the rear jack points. I like the rear jack point to be around 3/8” (max of 1/2”) higher than the forward jack points.

By increasing front R damping you’re trying to push the inside wheel (e.g., when turning to the right, the right corner is the inside corner) down onto the ground to take more advantage of the extra grip available from the inside tire. Don’t go crazy with the increasing R unless it’s just a trade to what happens. Always start at fully opened, or closed, (I prefer open) R and then count off the number of clicks you wanted noting what the old and new settings are. If you don’t do this and a corner is already adjusted wrong you’re likely making things worse or creating an issue that wouldn’t have happened if things were adjusted correctly initially. Second, you’d also try reducing rear R damping (same thing, start fully opened or closed, noting new and old settings) to help with (speed up) transferring cross weight to the front outside wheel. Be careful to not create new issues at other corners unless you’re intentionally doing a large change as a trade.

I actually find I’m faster with a 20 mm stagger (285 F + 305 R or 295 F + 305 R if the 295 is narrower). I know staggered setups aren’t popular here but I find it faster due to being quicker on throttle. Yes, I lose out on not being able to rotate front-to-rear but I gain it back with better performance.

[RugbyBro]

Originally Posted by Track/S

I found this MOTON article where they say that to combat understeer, stiffen the rebound at the front, I'm trying to combat understeer on my m2c with 285/30/18 square (Before with 285/35 tires I had no problems) my GTS turns much better with 275F/285R.

Maybe make the front end compression a tad softer and/or bump the rebound a tad? The tire profile switch would have increased stiffness all around but sounds like it's disproportionately affecting the front end? Lot of variables here.

While getting used to the new tire setup over the weekend I had some oversteer bias tuned out by dropping rear compression and increasing rear rebound. Not massive swings for each, just a -1 click compression and +2 clicks rebound.

[Track/S]

Originally Posted by M3SQRD

Are you experiencing understeer at initial turn-in only or understeer at corner entry and/or midcorner and/or corner exit with throttle? What are your spring rates and ride heights (i.e., how much forward rake are you running)? I measure rake by measuring the ride height right in front of the forward jack points and the ride height just right behind the rear jack points. I like the rear jack point to be around 3/8” (max of 1/2”) higher than the forward jack points.

By increasing front R damping you’re trying to push the inside wheel (e.g., when turning to the right, the right corner is the inside corner) down onto the ground to take more advantage of the extra grip available from the inside tire. Don’t go crazy with the increasing R unless it’s just a trade to what happens. Always start at fully opened, or closed, (I prefer open) R and then count off the number of clicks you wanted noting what the old and new settings are. If you don’t do this and a corner is already adjusted wrong you’re likely making things worse or creating an issue that wouldn’t have happened if things were adjusted correctly initially. Second, you’d also try reducing rear R damping (same thing, start fully opened or closed, noting new and old settings) to help with (speed up) transferring cross weight to the front outside wheel. Be careful to not create new issues at other corners unless you’re intentionally doing a large change as a trade.

I actually find I’m faster with a 20 mm stagger (285 F + 305 R or 295 F + 305 R if the 295 is narrower). I know staggered setups aren’t popular here but I find it faster due to being quicker on throttle. Yes, I lose out on not being able to rotate front-to-rear but I gain it back with better performance.

I changed the 140nm F and 150nm R springs to 120nm F and 130nm R, and I have the compressions at a minimum +2clicks, before I used more rebound at the back than at the front and the car felt much faster at the entrance and middle of corners.

I also did corner weight with this result, and yes, the back is a little higher:






Aligment:




Toe adjustment on the image is inverted.
Front toe out 1mm
Rear toe in 2mm






This weekend I will try with stiffer rebound at the front and stiffer compression at the rear, if that doesn't work I will install stock front swaybar to test.

Originally Posted by RugbyBro

Maybe make the front end compression a tad softer and/or bump the rebound a tad? The tire profile switch would have increased stiffness all around but sounds like it's disproportionately affecting the front end? Lot of variables here.

While getting used to the new tire setup over the weekend I had some oversteer bias tuned out by dropping rear compression and increasing rear rebound. Not massive swings for each, just a -1 click compression and +2 clicks rebound.

I go with minimum compression front and rear, I will increase the rear compression a little to see if it improves, oversteer is easy to combat, understeer is terrible... when I use the GTS I always amaze how it can turn so well

[M3SQRD]

Originally Posted by Track/S

I changed the 140nm F and 150nm R springs to 120nm F and 130nm R, and I have the compressions at a minimum +2clicks, before I used more rebound at the back than at the front and the car felt much faster at the entrance and middle of corners.

I also did corner weight with this result, and yes, the back is a little higher:


Aligment:


Toe adjustment on the image is inverted.
Front toe out 1mm
Rear toe in 2mm


This weekend I will try with stiffer rebound at the front and stiffer compression at the rear, if that doesn't work I will install stock front swaybar to test.


I go with minimum compression front and rear, I will increase the rear compression a little to see if it improves, oversteer is easy to combat, understeer is terrible... when I use the GTS I always amaze how it can turn so well

I’m assuming you’re running a coilover rear, yes? 120/130 N/mm = 685/752 lbf/in should have a more neutral/oversteer balance. Surprised you’re complaining about understeer. 130/150 N/mm might be a good combo to try if the understeer is that bad. This will shift the balance towards the rear + provide better front camber support. Why did you swap the 140/150 N/mm springs? Is the understeer in just certain corners or is it everywhere?

+2 from fully open? If it’s just two clicks from fully opened then I doubt your issue is too much C damping. Is C damping the same at the rear? Does the setup give you a feeling of confidence? How many clicks of R and C do you have? Are the dampers 2-way? What sway bars are you currently using and is it front only? Are they adjustable? If they’re adjustable, soften front or stiffen rear or both (if the understeer is absolutely horrible). I’m still wondering if the front 685 lbf/in spring + front sway bar aren’t stiff enough to maintain front camber with compression?

Low front negative camber, -2.0, is the only thing I would adjust. Is there a reason why you’re running only -2.0? If it’s because it’s street driven, I’d go to at least -2.5 deg if it’s a dual-purpose car, min of -3.0 if it’s not. When you switched tire sidewall height, is it the same or different tire brand/compound?

I always work on the end that’s having a problem rather than adjusting the end that doesn’t. Adjusting the good end usually results in two ends not working the way you want!

[Track/S]

Originally Posted by M3SQRD

I’m assuming you’re running a coilover rear, yes? 120/130 N/mm = 685/752 lbf/in should have a more neutral/oversteer balance. Surprised you’re complaining about understeer. 130/150 N/mm might be a good combo to try if the understeer is that bad. This will shift the balance towards the rear + provide better front camber support. Why did you swap the 140/150 N/mm springs? Is the understeer in just certain corners or is it everywhere?

+2 from fully open? If it’s just two clicks from fully opened then I doubt your issue is too much C damping. Is C damping the same at the rear? Does the setup give you a feeling of confidence? How many clicks of R and C do you have? Are the dampers 2-way? What sway bars are you currently using and is it front only? Are they adjustable? If they’re adjustable, soften front or stiffen rear or both (if the understeer is absolutely horrible). I’m still wondering if the front 685 lbf/in spring + front sway bar aren’t stiff enough to maintain front camber with compression?

Low front negative camber, -2.0, is the only thing I would adjust. Is there a reason why you’re running only -2.0? If it’s because it’s street driven, I’d go to at least -2.5 deg if it’s a dual-purpose car, min of -3.0 if it’s not. When you switched tire sidewall height, is it the same or different tire brand/compound?

I always work on the end that’s having a problem rather than adjusting the end that doesn’t. Adjusting the good end usually results in two ends not working the way you want!

Yes, rear is full coilover, 140nm front and 150nm rear is too harsh for street use.

3way coilovers, 20 clicks for low speed and 20 for high speed, 18 for rebound.

Front and rear sway bars H&R, 2 point adjustmen on front and 1 on rear.
Front and rear GT4 kinematics, don't necessary more than -2 of camber for street use.

This morning I did tests, stiffer rebound helped a lot, I think the problem may come from the tires since apart from the understeer it doesn't pull like before, so I understand that I should go back to the tires I used before, 285/35/18 (different brand and compound) This reminds me that it also happened to me with the cup2 in the rear...


With the previous tires I didn't have the problems that I have now so the problem comes from there I think.

[RugbyBro]

Originally Posted by Track/S

This morning I did tests, stiffer rebound helped a lot, I think the problem may come from the tires since apart from the understeer it doesn't pull like before, so I understand that I should go back to the tires I used before, 285/35/18 (different brand and compound) This reminds me that it also happened to me with the cup2 in the rear...


With the previous tires I didn't have the problems that I have now so the problem comes from there I think.

Here's a very non-scientific spitball - maybe the 30 sidewall isn't giving you the necessary compliance so it is not maintaining grip in the front with your setup (could be skipping a bit), hence why the additional rebound is helping. I love a thick sidewall so im all for you going back to 285/35.

[Track/S]

Originally Posted by RugbyBro

Here's a very non-scientific spitball - maybe the 30 sidewall isn't giving you the necessary compliance so it is not maintaining grip in the front with your setup (could be skipping a bit), hence why the additional rebound is helping. I love a thick sidewall so im all for you going back to 285/35.

I think the same but why does the GTS with 275/30/19 turn a lot better? It may be sidewall of that brand is softer...

[RugbyBro]

Originally Posted by Track/S

I think the same but why does the GTS with 275/30/19 turn a lot better? It may be sidewall of that brand is softer...

What are all the tires in question? I know one of them is AD09s but don't know about the others.