I think I posted this a while back, but the absolute most accurate way to
determine proper tire air pressure is with a tire pyrometer (thermometer).
This is what the big boys (racers) use. You make your run on the track or
skidpad, then immediately take temperatures of the tire tread, one at each
edge of the tread and one in the middle. All three temperatures should be
very close. If not, you can determine if you have the wrong air pressure,
poor alignment, or any other number of chassis problems (when taking temps
at all four tires).
For example, a higher temperature at the center of the tread indicates
over-inflation, higher temp at the edges indicates under-inflation, higher
temps at one edge indicates alignment problems. By comparing temps between
front and rear tires, you can determine which end of the vehicle is working
the tires harder, then adjust the vehicle to work all four tires the same.
You can also determine if you're working the tires to the max, or if you
could maybe use a stickier tire for track conditions. Again, this is rather
high-tech stuff if you delve into it too far, and is what INDY and CART
racers, etc. use. However, determining proper tire air pressure is quite
simple ;-)
Unfortunatey, a tire pyrometer costs several hundred dollars. If you belong
to a Circle-Track club or other road-racing club, it may be a useful tool
for the club to purchase. Also, an auto parts store that rents specialty
tools may have one......
-- '92 Dak CC 2wd 318 3.55 '84 GoldWing Interstatep.s. - Just found one of my old posts - here it is:
Actually, the correct term is "tire pyrometer". I did a web search on AltaVista and got 58 returns. Went to the first one and they had one listed for $348 (OUCH!!) - it's a race piece with 10-number memory, etc. Maybe a specialty shop would rent them out, or maybe you can rent or borrow one at a local racetrack. For just checking tire pressures, the procedure is pretty simple. If you want to do some more extensive chassis tuning, read on:
Some race car builders (at least chassis tuners) consider the tire pyrometer to be the single most valuable tool available to set up a race car or hi-po street car. Some of the things you can measure with just this tool are: correct tire pressure, handling balance, correct static camber, correct toe-in/toe-out, if car is being over-driven for the tire tread compound, if car is being driven at the limits, even if rim width is too narrow for the tire!
For optimum results, you need to know what temp your tires should be running (you'll probably have to get this from the manufacturer or tire engineer) - most tires run between 165 and 250 degrees F. For all-out tests, cars are usually run at max. g on the skidpad and temps are taken on outside tires, then car is run opposite direction on skidpad and temps taken on those outside tires.
Examples: If tires too hot, tread compound is too soft for track conditions; front tires too hot, understeer or front tire pressures too low; rear tires too hot, oversteer or rear tire pressures too low; inside edges too hot, too much negative camber, too much toe-out; outside edges too hot, too little negative camber, too little toe-out, too much toe-in, wheel too narrow for tire; center too hot, tire pressure too high; edges too hot, tire pressure too low; all tires too cold, tread compound too hard for track; front tires too cold, not enough load on front; rear tires too cold, not enough load on rear..........
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