124Spider

Hi,

I seem to have reached the point where, with a staggered setup, the car either pushes too much or has rear wheel lift (depending on sway bar setting). This is autocross.

Background: MY 2004
Stock, except for revalved Konis, Gendron medium stiff bar, SSR GT7 wheels of stock-legal offset, and Kumho 245/45-17 front and 275/40-17 rear

I was gridded today at an NT next to a guy with stock shocks and the stiffest Gendron front bar, and 275 Hoosiers all around. He says the amount of rubbing is acceptable, and the combination gives him neutral handling without rear wheel spin.

I'm having trouble seeing how 245's all around would be better than what I have, overall, but, if I can get enough contact patch out of 275 front tires (and little enough rubbing), I would probably go there.

I've done a search, but all I found was individual discussions of square setup, but not discussing 275's. If this has already been discussed, I would appreciate a link to the thread, and perhaps Steve could put something in his setup FAQ about square tire choices.

Thanks.

sirbunz

General consensus is that you need some really stiff shock compression to keep the tires off the fender liners in a non-CR. I would recommend trying a 245 non-staggered setup. Tommy Pulliam ran this on his car and did really well with it.

Edit, here is the link I posted in the setup FAQ. Also, with our typical bumpy auto-x lots, wheel lift is simply going to happen when you really hooking up. I just minimize as best as I can without compromising grip.

https://www.s2ki.com/forums/index.php?showtopic=610918

-Marc

124Spider

Interesting thread; thanks!

But I can't find a consensus there. I have the revalved Konis, set at full stiff front and 3/4 stiff rear. Is that enough damping to make 275's work on the front of a "normal" AP2?

I don't mind some rubbing; I just don't want serious damage, either to my fender or my tires.

If not, I have trouble understanding how 245's all around, with the FSB set at a very stiff setting, would solve my overall handling problems. I understand that the push might be "solved," but at the expense of rear grip; no extra front grip (so then I would be drifting where I now push; not a huge improvement, I fear). I don't see how that would get me though tight turns any faster than I can now (by keeping the FSB at a firm enough setting to prevent wheel spin).

sirbunz

Good questions. I think the only answer would be to get another set of wheels and tires and try this out. I suggest getting old 275s to test with the fronts to see if the clear enough. With the 245, the only answer I have is with Tommy Pulliams results with his '06 AP2. He drove this at '08 Dixie Tour, '08 Atlanta Tour, '09 Dixie Tour and local events. He drove other cars at the other and most recent events. Jadrice drove on the 245/245 setup and really liked it as well. I don't have many details from his perspective though and he used this on his CR.

-Marc

sirbunz

BTW, what is your alignment settings?

124Spider

I'll try to find a set of old 275's to put on my front wheels.

My alignment, for this, my daily driver/autocross car, is -1.75 front, -2.5 rear, max/even caster (5.5, I think), and (I think; it's been over a year since it was set) zero toe all around.

sirbunz

Backing the rear alignment down to 2.0 really helped the rotation in my car. Other than that, simply having it checked will be a good idea. My alignment would wonder quite a bit in a year.

-Marc

PedalFaster

In theory, taking grip out of the end that's working well shouldn't make you any faster because you'd already have been driving perfectly to the limits of your front tires' grip, and no faster. In practice, taking grip out of the end that's working well generally does make you faster because it's impossible to consistently drive perfectly, and having a car that's neutral gives you more options to place the car and correct for mistakes than a car that's terminally pushy.

Well, you'll want to tweak your setup so that the car's neutral, not loose.

Keep in mind also that a 275's pretty pinched on a 7" rim, so the difference between a 275 and a 245 on the front of an S2000's likely not as big as you're imagining. Recall the experimentation that David and I did with running 245s and 285s on the RX-8 -- our results, and those of other people who tried both combinations, were inconclusive.

124Spider

Is there a difference in dimensions of the Hoosier vs. the Kumho 275/40-17, which would make one more likely to fit well enough?

Orthonormal

A few points: Guy Ankeny ran 275 Hoosiers on the front of a non-CR AP2 with Konis that he valved himself, and had to replace the front fender liners after about 60 runs.

The Kumho will be far more difficult to mount to a 17x7" wheel, if it's even possible. I doubt that there's enough difference in size to significantly change the amount of fender liner shredding.

I would go along with the suggestion to reduce your rear camber. That is going to simultaneously cut down on wheelspin (because the inside tire is flatter on the ground) and reduce understeer. My rear camber is closer to -2.0 and the car works well with 245 tires all around or with 275 tires on the rear. I run with the 1.25" solid Gendron bar set to full stiff with both setups.

Folks around here (Reijo & Ron, Joey & George) tend to switch back and forth between 245 and 275 rear tires mostly for the purpose of optimizing their gearing for the course, and it doesn't seem to affect the handling balance much.

I think that the 245 square setup is good, but I think your problem lies more with your alignment.