What are the tradeoffs of higher tire pressure for AX ?

[sugarwood]

We are told to increase PSI for AX.
I guess this is to reduce sidewall flex.
So, what is the trade off ?

I think lower PSI would be harder to lose grip.
When the tire is softer, I guess there would be more lateral give (sidewall flex) before the tire brakes loose.
It would seem easier to do a "peel out" with hard tires compared to softer ones.
Dragsters seem to have lower PSI for that crinkly tire flex for more grip.

Does raising PSI also reduce traction since there is less lateral give?
Or does an over-inflated tire lose some grip b/c the contact patch is smaller?

[Flieger]

You really need to try different tire pressures and find the best ones for your car, tires, and conditions. Over-inflated tires will have a smaller contact patch. Under-inflated will roll over onto the sidewall, increase rolling resistance, and just feel mushy.

You might be able to convince someone with a similar car and tires to give you starting points to work with.

[Driven97]

There's a sweet spot where tires work best - it's different for every tire / car combo.

As stated above, too much, the contact patch is reduced and you have less grip. Too low and you're on the sidewalls, and you have less grip. In AX competition, I've run as high as 40psi and as low as 29psi with success. I'm running new tires this year, and trying to figure out pressures. They seem to have very little clock time difference between 30-35psi, changing pressure only seems to change the feel. Previous tires definitely had a more narrow "happy place."

I've also seen cases with non-performance based all season tires (soft sidewalls,) on heavy, camber challenged cars where even 40psi was insufficient. An experienced autocrosser should be able to show you how to mark your sidewalls to check for rollover. I like to err "too high" with newer people because it's a lot easier to let air out than put more in.

If you're just starting out - don't fret too much about pressure. Just make sure you have enough, and focus on driving and learning to extract speed out of what grip you have. That's way more important to getting faster than worrying about a psi or two.

Good luck.

[Charles Freeborn]

If the pressure is too low and the tire is rolling onto it's sidewall it will lift the tread off of the ground, thereby reducing contact area. My dunlop's have little arrows on the sidewall showing how much roll over is happening. Sometimes I'll put a dab of chalk on them (for contrast) and check after each run.

-C