Determining optimum tire pressure for AutoX?

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Determining optimum tire pressure for AutoX?

Postby tbdomenz » Thu Jul 22, 2010 3:05 pm

Short of buying a pyrometer to check tire temps, whats an intelligent procedure to find out if you are getting the most from your tires during AutoX events? Running FalkenAzenas 235/45/17 on 9" wheels with -2.5 camber all around.
Thanks
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Re: Determining optimum tire pressure for AutoX?

Postby Brian » Thu Jul 22, 2010 4:32 pm

Well, if you don't test and measure with pyrometer, then test and measure by the clock. The pyrometer doesn't tell the whole story anyway, for numerous reasons we won't get into right now. Test against the clock on a practice day. Sometimes a pressure setting that is not ideal for temperatures will, nonetheless, 'feel' better to the driver and if the driver feels more confident that often translates into faster times.

IF you really want to do it right, BEST way to do this is DRIVER BLIND. You need a practice day where you are going to get 12 runs or more. You need somebody else to set the pressures for you while you are in the car with your ear plugs in....so you don't actually know what you are driving on (this is a whole other issue but I always autocross with earplugs in...try it and go faster!). And you need to bracket and control, repeat....to see if your results are legit. Many drivers are consistent enough to make this work, many are not. See Grassrooots MotorSports Magazine tire tests (in nearly every other issue and often posted online) for examples of reasonably good testing by clock.
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Re: Determining optimum tire pressure for AutoX?

Postby slartibartfast » Fri Jul 23, 2010 12:52 pm

Another method involves marking a sidewall.

Use white shoe polish or chalk to make a line radially from the outermost groove on the tire face past the edge of the shoulder block. Make a run and note how much of the line was worn off. Typically, it is (or was) recommended that you not roll the tire over past the shoulder block. Add air if you do so. You do want the shoulder block involved with cornering, so you let air out if you didn't wear any of the mark off the shoulder.

This is a starting point. Tweak air settings as needed for you driving style, surface, temperature, etc.

I learned this over a decade ago driving a Sentra SE-R. I don't know if RWD can use this method or if some other simple and cheap procedure has trumped it since I quit AX.
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