Chad,
Without knowing what your suspension setup is (both hardware and
geometry), including wheel width and offset,
I'll give you a couple of "rules of thumb". With front wheel drive,
you generally want a 5 psi spread front to rear (+5
psi in the front). If possible, replace the air in the tires with
dry nitrogen. Here in San Jose, a lot of tire shops,
including Costco, use nitrogen when installing new tires. Your
pressures won't increase as much when the tires
heat up, which can be a real advantage on the track. Tires with a
speed rating of VR (149mph), or greater,
the max pressure rating (molded into the sidewall, down near the
bead) will usually be 40-50psi. I't's not a good
idea to exceed that, and I've never had a set of tires that required
going above the max to get them to work right.
The last couple of sets of tires I've had on my '92 GTI 16V (Toyo
Proxes T1s & GoodYear F1 GS-D3, 215/40-ZR-16)
have worked well with 36 psi/front, 31 psi rear. That's for very
hard street driving. If I took the car to the track, I'd
probably end up raising the pressures to maybe 40 psi/35 psi. The
"real" way to determine if you're pressures
are correct, is to take temperatures across the tire's tread surface
with a infrared temp gauge after running a few
fast laps on a road course, or after a run through an auto cross
course. Assuming your suspension setup is close
to correct, if your tire temps are consistent across the tread, then
your pressures are about right. If they're higher
in the center of the tire, then the pressure is too high. If they're
higher toward the side walls, and lower in the center,
then the pressure is too low. The same method can be utilized to set
up the suspension. If the tire temps tend to run
higher toward the outside of the tread, you probably need more
negative camber. If the reverse is true, then dial in
less negative camber. Keep in mind that all this stuff is inter-
related, so you only want to change one thing at a time,
make a run, check the temps, then make another change accordingly.
--Holland
[email protected]
On Jun 29, 2007, at 2:07 PM, Chad Rebuck wrote:
For 195/50-15 performance tires (not racing compound) what pressures
should I use for the track? The driving time will be limited to 15-30
minutes at a time. I think its more of an extended auto-x instead of
all out driving at a racetrack. What method do people use to come up
with the right pressure?
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