Re: Tire Inflation

[Chris Newbold <cnewbold@eznet.net>]

SOP8920@Siena.edu wrote:

> I read a book about auto-racing written by Bob Bondurant a year or so ago. He
> claimed that today's tires are capable of much higher pressure than the
> side-wall markings indicate. In fact, he usually ran his tires at (from what I
> recall) ~45 PSI on all the cars used in his school. That included the bondurant
> ...

Okay, okay. Now I'm really confused about all this tire pressure stuff...

Everything that I've heard here on the list and from a fair number of others
face-to-face is that you want high(er) pressures in a track situation. I
understand why: less deformation = less heat, stiffer sidewalls = less roll-over,
etc., etc.

Now, the last time I was at Watkins Glen, I got to talking with some very
experienced folks (not Bondurants, but...) about pressures. What they came
up with WRT to my Audi was very different. They're recommendation was to shoot
for ~38 PSI *hot*, maybe even less, say 36. More tread on the track = more traction!

This was actually born out in empirical testing. I ran ~38 PSI hot (as measured
immediately after coming off the track; turned out to be ~32-34 cold): inspection
of the front tires revealed that there was 1/8"-1/4" between the edge of the
visible wear and the edge of the tread, so no roll-over. And the car understeered
noticably less than before (when I was running 38 PSI *cold* [ ~42-44 hot]).

The tires are nothing too special, Yoko U+4s; the car a '93 90CS FWD-only.

Go figure.

-Chris