Does anyone have any suggestions for tire pressures? Im new to autocross and am unfortunetly running Michelin Pilot runflats. Ive seen the threads on conventional tires, but not runflats. Any help?
Try heading to high thirties, low forties. I offset the fronts to be two to five pounds less than the rears. I do run Hoosier Racing Tires, which are quite different from your runflats.
When I first got into autox, I did as the novice instructional guide recommended and bumped my cold pressures up a 4 to 6 PSI. The idea being to prevent the sidewall from rolling over too much. I've asked instructors at the BMW Performance Center what they do and they run stock (as listed on the door jamb) tire pressures. They tell me that that pressure gives the tire optimum contact patch for high performance handling. Of course if you go to a different tire size, you'll have to adjust that baseline pressure. Your tire guy can help you with that calculation. I've found that when running closer to the stock, I have better grip. When I run at "overinflated" pressures, it feels more skatey. I attribute that to the smaller contact patch that results from over pressure. Yes, I see a bit more wear on the tread corner, especially the fronts, but with 40/35 series or shorter sidewalls, the stiffer sidwall of the lower profile seems to limit such rollover. I don't see any scrub beyond the tread block edge or down the sidewall. I'm not sure but I suspect the advice to over inflate tires for autox came from the day when folks were running 50/55 series profiles. Most of the vehicles at the BMW PC are on run-flats. I suspect their stiff sidewall would work particularly well with stock pressures. I'm be interested to see what others think.
I can't remember what I used to run on street tires. But lately I've been setting the NT01's at 32psi cold, and that has worked out well (on a 255/40/17 sized tire).
The usual gang of suspects gets cooking on the topic of autocross tire pressure toward the middle of this thread: http://bmwcca.org/forum/showthread.php?t=2849 With my 195/65-14s on my 1987 325ic, I ended the autocross season running with 43 psi in the fronts and 38 psi in the back. Chalking the tires and having an expert give me advice was very helpful to settle on these pressures.
Man, I dunno. I know what I run, too, but that's on R compounds on an E28. Iwouldn't even know where to guess as a starting point for run-flats. That's a whole different universe from us mere spare-tire-carryin' mortals ...
