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Old Mon, May-10-2010, 10:29:21 PM   #14
SilberFuchs
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Quote:
Originally Posted by Obioban View Post
Argh, that article does have me bothered. The problem I'm having is that the data in there doesn't jibe with what I've seen in reality.
-lateral Gs don't drop with wider tires without a decrease in tire pressure
-drag racers run super low pressures on the rear
-you can easily and noticeably shift the balance of a car by tweaking tire pressures.

.... but I am considering rewording that section now. I certainly don't want to mislead people and post something that isn't true....




Edit: This is where that test gets really werid. They actually get less deflection and lower tire pressure than high. Something must be amiss...
Ian, I am certainly no expert on tires and pressures, but I'm not quite sure your statement about different tire widths at the same tire pressure leading to the same grip is quite correct (UNLESS a higher tire pressure is required for a wider tire bearing the same load to get the same full thread contact patch). My understanding (albeit limited) about tire pressures is that it's about optimizing even and full contact patch for a given axle load, thus leading to maximal thread contact patch and even tire wear. For example, since the M3 has a near perfect 50/50 weight ratio, the front and rear tire pressures should be about the same, unless one wants to dial more or less understeer/oversteer by messing with inflation pressure. Also, the tire pressure is dependent on the driving conditions -- in other words, while a certain pressure may be ideal for mostly straight line driving (highway, slow city, etc.), it may be too low for an autocross event or high-speed cornering at the track which require higher pressures due to high lateral weight shifts (thus, the chalk test to get the optimal pressure) so as not to ride on the shoulders of the tires.
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Last edited by SilberFuchs; Mon, May-10-2010 at 10:53:16 PM.
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