VetteDrmr

Can someone kindly explain to me the rule of thumb stating that if you want to reduce oversteer, you add pressure to the rear tires? Same rule is stated for understeer, as well.

This seems counter-intuitive to me. I would think you'd want to run the minimum amount of air that keeps the sidewalls from rolling over. Clearly I'm not understanding, but it *is* a Monday.

TIA, and have a good one,
Mike

cgh1

Adding pressure stiffens the tire, thus adding spring rate - you're stiffening the suspension. Of course this has its limit. If you over inflate, you can reduce the amount of tire on the pavement. Just like anything, too much of a good thing is no longer a good thing. And that's not going into the temperature conversation.

But anyway, the "rule of thumb" is stiffer=better, pressure=stiffness.
Hope this helps.

VetteDrmr

Ok, that makes sense, as long as you're staying within the pressure range that let's you keep the full contact patch on the ground.

Now, check this thread for my recent experiences: http://forums.corvetteforum.com/zerothread?id=793536

So, have I been running WAY too much pressure in my rear tires? Or, do the tires just need some more "break-in"? Or, do I need to ADD pressure, which seems like going the wrong way to me? Or, do I need to just make an adjustment and see what happens?

Thanks for the reply,
Mike

BrianCunningham

VetteDrmr, why are you running 275's on all 4 on a C5?

That works well for a C4, but they were designed to be run "square".

I'm not surprized your having problems.

69autoXr

Also keep in mind the fact that (you said so yourself) your fronts tires are worn nearly slick, but your rears are like brand new. You therefore have much more contact patch in the front than the rear. In that guide I supplied you with it says to reduce oversteer (add understeer) decrease the rear tread depth.

cgh1

Brian's got a point - for Auto-X, you might simply have too much meat up front. I have done very little aggressive Auto-X in a C5, so I can't say I've ever done so with a setup like yours. Only stock sizes have I driven.

~chuck

VetteDrmr

Good points all.

Brian, the reason I went with 275s all around came from 3 things:

1. Every C5 I've autocrossed in or observed people autocrossing in have had serious understeer issues when running stock (245 f, 275 r) size tires.

2. One of our fastest autoxers, when running his C5 FRC, was running 315s all around, and said that the car was nicely balanced.

3. I actually wanted to run a 275 f, 285-295 r, to get a little bias towards understeer, but the next size up in the Toyo RA-1s from 275 is 335. :eek:

Chris, it very well might be that I've got a bigger contact patch with the worn tires and that's the difference.

Most likely, it's that nut on the steering wheel that needs adjusting the most.

Thanks, all, again, for the suggestions.

Have a good one,
Mike