Spring rate too high?

[AndyK5]

Stock car on stock Federal 595 RS-RR with whatever stock alignment was understeering alot.

Now has MCS2W with vorschlag, rear toe links and front sway bar end links. Alignment is -3.7 camber 0 toe front -2.5 camber 1/8inch in toe rear. Spring rates are 12k (672lb) front and 11k (616lb) rear.

Tires are on their 5th track day and fronts corded on the last session, 65F ambient.

Damper settings are stock which are on the soft side of things, 4 out of 14 compression, 8 out of 18 rebound. 12 bar nitrogen pressure.

Now the car oversteers a lot under trail braking. It does not behave too bad under power, power oversteer is not an issue.


This week I am going to square setup and 275 front which should technically make the front even grippier. Car has no aero or power mods.


Are my rear springs too stiff causing the oversteer?

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[GRGT4]

You may not want to chase the setup too much with that much time on the tires. See how it goes with the new set.

 

[Islindur]

Stock sway bars?

 

[AndyK5]

You may not want to chase the setup too much with that much time on the tires. See how it goes with the new set.

I was thinking the same thing, but fronts are just as worn as the rears, maybe even more. Again though who knows, test with a fresh set will yield better metrics.

Stock sway bars?

Yes

 

[kyle9]

Looking purely at spring rates and ignoring everything else, I’d say they are too low compared to what everybody has found to be successful for time attack.

I’ve had similar problems before and there were several issues that seemed to contribute:

- damaged rear dampers (caused by impact with rear end links)
- improperly adjusted rear sway bar
- improperly adjusted rear end links
- improperly adjusted rear traction arm causing excessive bump steer

Heat cycled tires seems to cause the rear to break loose as well, even when the front are equally cycled out.

 

[GRGT4]

Has anyone really analyzed the stock ABS strategy and effects? Pretty safe to say that if you are on track with toasted tires and get hard into the ABS up front, it will go into as much as full "oh shit" street mode which typically dumps the front pressures and and would leave you with heavy rear bias and some lovely oversteer during trail braking as described, until the front recovers.

Just one of several other things to possibly consider before throwing changes at it.

 

[AndyK5]

Looking purely at spring rates and ignoring everything else, I’d say they are too low compared to what everybody has found to be successful for time attack.

I’ve had similar problems before and there were several issues that seemed to contribute:

- damaged rear dampers (caused by impact with rear end links)
- improperly adjusted rear sway bar
- improperly adjusted rear end links
- improperly adjusted rear traction arm causing excessive bump steer

Heat cycled tires seems to cause the rear to break loose as well, even when the front are equally cycled out.

My dampers are brand new so hopefully they are in good condition and properly charged as I did not check the pressures. The other thing is the person who installed the dampers was supposed to put them on stock settings and after a few sessions I found the adjusters to be all over the place. Now I am not sure if he even charged the front dampers to proper nitrogen pressure. Will be investigating today.

Sway bars are stock, rear endlink is stock. Rear toe bar is aftermarket.

Has anyone really analyzed the stock ABS strategy and effects? Pretty safe to say that if you are on track with toasted tires and get hard into the ABS up front, it will go into as much as full "oh shit" street mode which typically dumps the front pressures and and would leave you with heavy rear bias and some lovely oversteer during trail braking as described, until the front recovers.

Just one of several other things to possibly consider before throwing changes at it.

So that would make sense, though this is happening in corners where ABS did not kick in , or kicked in like a few seconds earlier. Over steer is comes when trying to tuck back in to the apex at about 20-30% brake pressure.



Maybe its a driver issue, maybe I have too much trail brake pressure.

 

[GRGT4]

It would be interesting to monitor the ABS/ Pressures. I don't have any knowledge about the strategy of this stock system, but with many others in that situation they don't just fully recover right away. If you know their was activity, it seems even more likely to me that there could be a lingering balance shift. Best thing to do is to try a less aggressive/more progressive application to stay out of the ABS, and see if it affects things. Either way, if you say the car is good under throttle then you'll want to back things up and get rotated sooner anyway to be back under throttle well before most apexes. Anyway, just sharing thoughts in case it helps...

 

[kyle9]

Try new tires and make sure your rear ride heigh is stock.

If you drop the rear height you'll mess up the geometry and the rear end will be really unpredictable, especially without any adjustable arms to (kind of) fix things. You can't really drop the rear ride height much unless you run the Verkline subframe to correct the geometry.

 

[AndyK5]

Try new tires and make sure your rear ride heigh is stock.

If you drop the rear height you'll mess up the geometry and the rear end will be really unpredictable, especially without any adjustable arms to (kind of) fix things. You can't really drop the rear ride height much unless you run the Verkline subframe to correct the geometry.

What is the stock ride height and where do I measure it from? I told my alingment guy to leave it stock but not sure of he did it. Right now I have 1.5 finger in the wheel well on stock wheels and I think stock is more.


Also going down to 18 inch wheels…still stock height? I’d have to raise the car .5 inch to get there to make up for 1 inch diameter change of the wheel.

 

[kyle9]

Sounds like you’re too low. Lots of people have posted stock height measurements. Ground to fender I measured 27.75 with oem wheels and tires (32psi) in the rear.

 

[AndyK5]

Sounds like you’re too low. Lots of people have posted stock height measurements. Ground to fender I measured 27.75 with oem wheels and tires (32psi) in the rear.

Do you know front and rear is supposed to be same? There is no front/rear rake in the stock setup?

 

[CafeRacerQueen]

Just run a taller overall wheel/tire diameter from stock

 

[racebuild]

Stock is 14.5” from fender lip to center of the hub.

 

[garudathree]

@kyle9 any willingness to share your fender to centercap measurements please?

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