I know next to nothing about autocross, but I suspect setups that work for a
race that is over in 20 seconds with a max speed of 40 MPH are not going to
be the same as one that lasts 20 minutes with a max speed of 130. In fact I
can't see how tire temps would be all that meaningful--I don't trust the
temps I take at the track because the straights are too long--the outside
edges get cooled off. That's why I use a skidpad.
I'm not saying that low pressure is better than high. My comment was that if
you raise the tire pressure more than you need to for the weight of the car
that the center of the tire will get hotter than the edges. Generally for
racing you want as even a tire temp as you can get, because that means the
tire is flat on the road from edge to edge during extreme cornering--which
is when you need the best contact patch. But there are a lot of variables
that can make the readings spurious. You could have perfect camber for
extreme turns, but when the car is going straight the contact patch will be
at the outer edges, with the inner edges hardly touching. That's a good
thing--less friction in a straight line and generally higher stability. But
the tire temperatures will be meaningless.
I dropped a second off Peyote's time last weekend by just optimizing this
stuff--and Peyote would be competitive in club racing, never mind vintage. I
think with the right gearing and an extra tug on my shoulder belts I could
get it below 1:30 at Portland International Raceway with the chicane. Mid
pack in the sports racer/formula Atlantic pack is 1:28. Not bad for a forty
year old Triumph in drag.
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of Jim Gambony
Sent: Wednesday, July 14, 2004 8:46 PM
To: fot@autox.team.net
Subject: RE: Yoko tire pressures
>Higher pressure than you need equals hotter in the middle of the tire,
>for
sure.
Bill, true.. But you need to look at the complete picture.
When I ran in vintage locally it was in a 1960s Austin Mini Cooper 1275S on
175/55/13 A008Gs A Mini prepped to the full extent of the vintage rules,
except for the 13" rims. 1380 pound car. Granted, I was mainly looking at
rollover on the tire sidewall.
I ran 42psi front and 28psi rear- my autocross pressures... when I ran at
Texas World Speedway. The local Mini expert thought I was on drugs. So he
did tire temps for me during practice and declared I was spot on.
Granted, FWD means higher temps in front. And how aggressive he drives also
decides how high to push the pressure.
At a local autocross I competed in my Spitfire against another Spitfire on
identical Yoko slicks. The other driver ran pressures in the teens.. I was
running 22 front/26 rear. All being said and done I was something like 10
seconds faster per run. Totally hooked up. On old second hand take off
tires.
And I view road racing as an autocross where you can shift up out of second.
:D
Cheers,
Jim
Dallas TX
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