I just had my first auto-cross event last weekend and it was a BLAST! I really learned a lot about my car and what it's limits might really be (even though I definitely didn't hit that limit as a novice driver)

My question is...

I used the pressures listed in the subject for the race. I really like the tighter response I get during normal street driving. I've always favored higher pressures in my wheels for everyday driving in my old saturn as well.

Are there any concerns I should have driving at that pressure in general other than preference?

I have OEM runflats (16") and they list their max PSI as 51

 

only that if you don't do a lot of hard cornering in your street driving, you'll wear the centers out before the edges.

 

What jakay11 said. If you want to check and see if you are wearing them evenly, get an infrared thermometer (I use my hand, but it is not that accurate) and test the center vs. the edges. If they are even, you should be fine. If not, then rotating them often can help, but you are still probably gonna wear away the center first.

 

A trick the drag racers use: You can do a short burn out and take a look at the tread marks left on the pavement. If it's darker in the center, then you are running too much pressure. If it's darker on the edges, not enough. Adjust until the pattern is even across the width of the tread. Although wearing off your tread in this matter might be counterproductive towards tire life, it will give you an idea of what pressure will allow you to put down the most even contact patch.

 

That might work well for straight line acceleration, but thats not going to give you a good indication of whats happening when cornering at the limit.

Jason

 

That's why "it's a trick the drag racers use".

The OP apparently wants to know what his tires will be doing at those tire pressures when he is just driving around on the street. He already knows he likes the response from those pressures in the turns "when cornering at the limit", right?. But as he's concerned about how they are going to wear when doing street driving, he needs a way to determine that wear. Such as with an infrared temp gauge (as scab mentioned), or by finding a way to check his contact patch so he doesn't prematurely wear out the center section of his tires by running too much pressure.

We aren't trying to answer what's happening when cornering at the limit, but if we were, there's a decent article on tire pressures, temps, and contact patches here:
http://www.turnfast.com/tech_handlin...ressure4.shtml

So if you want a contact patch that's optimized for cornering, you'll be wearing out the centers the rest of the time you are driving normally on the street. There's always a compromise, and the best answer depends on what each individual decides is most important to them (wear or cornering ability).

 

Thanks guys! The information around here is always awesome

I'll probably lower the pressure a bit to find a happy medium as I'm going to be facing a lot less cornering in my daily drives to work (especially here in IL).

Thanks again, I've got a good amount of stuff to chew on

 

I run about 36 psi with my BFG KDWs. They are a really stiff sidewall and thats what ive felt is optimal. The great things about the MINI is the steering gives a lot of feed back and you really can get a feel for tire pressures. mid 30s is about right for performance oriented street tires with a stiff sidewall, and bumping it up closer to max if the tire may have been more comfort oriented. Autocross is definitely a touchy thing and the tires can heat up, so it helps to constantly keep tabs on the pressures as the tires heat up. Its all a fine balance and every tire will be different. In the cold since you probably wont be getting much grip its probably better to run a little lower than the optimal warm weather pressure. If you are a novice you may want to go with saving your tires edges and just running the max pressure. Even at max pressure you aren't going to have a problem with wearing the middle of the tire too much at autocross.

 

There's nothing wrong with running 40F, 35R on the street all the time. The concerns about wearing out the center of the tire due to overinflation are left over from bias ply tires. Modern radial tire construction makes this a relative non-issue.

I've used similar settings (around 40psi, give or take a couple psi depending on cars and tires) on the street for 115,000 miles on my MCS, 80,000 miles on the previous car, and 239,000 miles on my wife's Forester. The higher pressures relative to OEM recommended settings only help most factors except ride quality.

In general, somewhat higher tire pressures result in:
-Decreased fuel consumption due to reduced rolling resistance
-Increased cornering capacity and improved steering response
-Longer tire life due to less heat (tire deforms less as it rolls)
-Increased ride harsness as the increased pressure in the tire makes it a "stiffer spring". Yes, the tire is a spring from a suspension viewpoint.

My wife doesn't care about the 2nd and 3rd points above, and hasn't noticed the 4th. Her car is also set for 0 toe front and rear to further help the 1st and 3rd points.

Scott
90SM