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Old 10-29-2008, 04:03 PM   #38 (permalink)
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Originally Posted by MazdaMatt View Post
I have raised my tires from 36/33 to 45/42. I notice longer coasts, rougher ride and DECREASED cornering and stopping ability on dry pavement.
Interesting. Are you using R-compound tires? Those generally grip better at relatively lower pressures. Hard-compound "real street" tires usually grip better at higher pressures. I do know that the tires I used to run (Yoko AVSes, that'll tell you how long ago it was! ) gave me better lap times at 40 PSI than they did at 36 PSI.

The above was autoXing, which places a significant premium on lateral grip. Braking and acceleration are not as important, so you can still get better lap times with worse longitudinal traction as long as the lateral grip is better.

Other tests I have seen recently (a recent Grassroots Motorsports issue) showed that higher pressures on the less-grippy end of a car (I think it was on the rear of a CRX) will result in more grip to a point--then the grip falls off. The higher pressures generally resulted in better feel (AKA "harsher ride") and less loss of grip than being an equivalent amount of pressure under the "maximum grip" pressure. However, the grip was less consistent, so it was sometimes harder to control. (I hope I don't have that last statement backwards, it's been a month or two since I read the article.)

I talked to some drag racing friends of mine, and they seem to agree that lower pressures let you launch better, so it sounds like for acceleration a lower pressure is better. I haven't seen much of a consensus for braking distances, though.

...Oh, and I have the tires in my CRX just below the sidewall maximum.

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