mryaknow

I autocross an SS classed 2004 Z06. My car is neutral on Asphalt, but I've noticed when competing on concrete the handling goes to understeer. I only run on concrete a couple of times a year.

I experience pretty bad understeer at mid-corner on concrete.

I'm running a common autocross Alignment.
Camber Ft -2.0
Camber Rr -1.5
Zero toe Ft
1/4" Toe in Rr
Stock Bars.

Is this a common problem when running on concrete? Are there any easy fixes in terms of tire pressure adjustments? Or is the problem just the loose nut behind the wheel?

Any help would be appreciated. Thanks

Matt

LehmanZ06

Possibly a throttle induced understeer.....a little to anxious with the gas ?

Front tires giving up at the limit slowly is confidence inspiring.

Possibly more front toe out ? (helps to point the car at initial turn in....not sure of midcorner effects)

mryaknow

Thanks for your reply. I have in the past caused throttle induced understeer, but in this case I was trying everything from closing throttle to trailbraking. Although I have always found it hard to trail brake the Z06 without kicking in the abs .

The strange thing is on asphalt a mid corner push has never been a problem. But on 2 different concrete surfaces I have consistently experienced pretty bad understeer.

thehammer69

Set front camber to -2.3

Toe the front out a hair.

Reduce rear toe to 1/8 to 3/32.

I think that may fix you up.

Do you have the car lowered? if so, how much?

waktasz

I'd go more front camber, and for me, a bigger front bar.

If you are too low you could be bottoming out the front shocks and washing out. You might not see that on an ashphalt surface because you aren't experiencing as many G's.

mountainbiker2

Just reduce the toe in at the rear. Go with 0 to 1/16" total toe in. If you're running Kumho V710's I would not put in more camber in the front. Hoosier A6 would require a little more camber in the front then you have. I would do the toe for my number one choice first.

Steve

mryaknow

Thanks to everyone. Your advice is greatly appreciated. So, it sounds like dialing in less rear toe is the first place to start. I'll try that out as soon as I can. I was also wondering if raising the rear ride height would be beneficial. Any ideas on this front?

Thanks again this forum is a great resource.

mryaknow

Hammer
I forgot to mention the car's ride height has been adjusted for corner weighting only. I have a steep driveway

Solofast

If you have poly bushings on the front go back to stock rubber....

If you have stock bushings on the front bar, put a 1/16 of an inch shim between the bracket and the frame. That will soften the front bar enough to fix the push. Adding more front bar stiffness would increase the push. You are obvioulsly close on setup and just need a little tweak to get it dialed in...

mryaknow

Thanks Solofast!

I am using the OEM bushings in the front. So, I will try adding a 1/16" shim on the brackets as you suggested. If that doesn't work I will try changing the rear toe as also suggested in previous post. I really appreciate your suggestion as this is a simple and easily reversible setup change and I would have never thought of doing that.

Thanks Again

Matt

TedDBere

Adding a washer under the sway bar brackets is SCCA SS legal, FWIW.

Add camber and 2 lbs of pressure to the fronts.

Dave OH32

Yeah it is. Very Much so in fact...

TedDBere

Well, I can learn. Where in the rules is it allowed? You can use any bushing material, you can use any bar and any endlinks. But I don't see where you can add spacers to the mounting positions to alter the bar geometry. But I can see where it probably wouldn't be any different from using offset bushings.

It's certainly not in the service manual as an acceptable adjustment, like shims for castor are.

talon95

The brackets are free, right? You could just make them with thicker ends. Same thing. The washers are legal (on the front of course).

Dave G.

froggy47

waktasz

I've always understood that the brackets/mounts for a front bar are free, but now that I check the rulebook I don't see where it says that.

I also don't see where it says endlinks are allowed either, for that matter.

TedDBere

Endlinks have always been allowed, but one of the last couple of Fastracks finally had the wording changed to include it in the rules, instead of having it implied as part of the bar. FWIW

waktasz

I know they are allowed, and have thought the brackets/mounts were as well, but there is no specific mention of it in the rulebook.

TedDBere

Here is the rule:

13.7 ANTI-ROLL (SWAY) BARS
A. For front anti-roll (sway) bars:
1. Substitution, addition or removal of any front anti-roll bars is
permitted.
2. Substitution, addition or removal of anti-roll bars may serve
no other purpose than that of an anti-roll bar.
3. The use of any bushing material is permitted.
4. No modification to the body, frame or other components to
accommodate anti-roll bar addition or substitution is allowed,
except for the drilling of holes for mounting bolts. Nonstandard
lateral members which connect between the brackets
for the bar are not permitted.
B. Rear anti-roll (sway) bars may not be removed, replaced, or
modified in any way.

And here is the Fastrack from July:

3. Stock: Section 13.7.A.1 is clarified to read: “Substitution, addition or removal of any front anti-roll bar and its supporting hardware
(brackets, endlinks, bushings, etc.) is permitted.”

So I suppose it would be argued that the addition of washers to the bracket constitutes "supporting hardware" and would therefore be legal.

See, I can learn.

froggy47

Rather than add a specific size shim/washer what you might want to try is adding an appropriate size washer(s) to get the bar to the point where it can be moved by hand when detached at the ends.

Bars/bushings/paint thickness/bushing material/grease all that stuff varies from car to car. Age/miles on the bushing also makes a difference.

Use the right combination for "your" car, sort of like hand fitting it.