I realize this is not the autocross list, but I have a few things to say
about the tire-pressure discussion. The things that Jim Muller and others
are saying about tuning your handling with tire pressures are not as true
with modern tires, especially low-profile super-compound autocross tires.
You have to tune your handling with the chassis, you can't do that much with
the tire. The best rule seems to be, run the lowest pressure you can get
away with without rolling the tire too much. Obviously, wide wheels are the
answer here. If you cannot use wider rims, use narrower tires. The object
is to prevent that sidewall rolling. I have to use over 50 psi in the front
on the Spridget with 4.5" rims. By changing to a 5.5" rim, adding a rear
sway bar, moving the battery to the trunk and using new bushings to get more
negative camber in the front, I hope to reduce my understeer by running LOWER
front pressures. A lower pressure puts more tire in contact with the road,
but you must not permit the rollover.
Jim is absolutely right about keeping higher pressures in the rear of a
Spitfire with high-profile tires on skinny rims. You also should invest in a
camber compensator of some type to prevent the "Ralph Nadar Effect". In our
autocross rules, we do not let Spits run without them.
Phil Ethier
THE RIGHT LINE, 672 Orleans Street, Saint Paul, MN 55107-2676
home: (612) 224-3105 work: (612) 298-5324
electronic mail: phile@pwcs.stpaul.gov or uiucuxc!pwcs!phile
It's Hip to be Octagonal.
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Login name: phile In real life: Philip J Ethier
Phone: 298-5324
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