I recently got a set of 17" wheels and R-compound tires for autocrossing. I had them on for a week then decided to put the stock wheels back on. When I looked at the tread of the new race tires, the rear tires looked like the middle of the tread was not worn at all! I believe the tires were at 35 psi. Wear on the outsides of tires usually indicates underinflation.

How do you know what pressure to put the tires at? I would think that 35 would be OK, especially once the tire heats up.

 

I've found it really depends on the tires. I can't commend on any R-compounds. I recently bought a tire pyrometer (Longacre ~$100) before my last autox and found I had the opposite problem. Ended up dropping the front tire pressures from 44 down to 37-37.5 b/c the centers were so much hotter! The rears are being run at 34 psi. These are the hot, post run pressures. Unless you can find someone with the same setup, I recommend getting a pyrometer and finding the pressure yourself. At least then you know what you've really got going on. Good luck!

Mike

 

At the track, I'm at 42 front 37 rear hot on 17" 245/45/17 V700s.

 

How many psi are your tires at cold? Based on your posts, 35 sounds about right. I will have to bump them up a little more to see if the wear is more uniform. 2 more weeks til auto-x, plus another auto-x all day clinic/practice held by the local Lotus club. I can't wait!!

How much are pyrometers?

 

35 front and 32 rear cold. Up here, there are at least 2 autoxes every weekend.

 

How much psi should I put for mine? front 245/35/19 & rear 275/30/19

 

Don't go by cold pressures. For me, "cold" pressures might be at 90 degrees, which might make the "hot" pressure 2 psi higher, whereas on a cool day in the NW "cold" pressures might be at 65-70 degrees, but the "hot" pressure might go up by 5-6 psi. When starting cold, I recommend starting about 2 or 3 psi below what "hot" pressure you're shooting for, then adjusting your pressures after your each autocross run.

P Diddy - a Longacre tire pyrometer is around $100. You'll have to search for a good price. They're pretty easy to find online.

palung - again, this totally depends on your exact tires. I would say around 38f and 35r, but that is merely a guess. For a given size, one front tire may run best at 45 psi, while another tire may perform best at 36 psi up front. Without testing yourself, you can't really know if you are over/under inflated.