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Maximum allowable vs. what's reasonable. Posted by Ari [Email] ![]() ![]() In Reply to: Tire pressure PSI, Yoni, Mon, 7 Jul 2003 15:25:31 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The 51 psi tire pressure is the MAXIMUM pressure- the Not To Exceed limit. There is almost no reason I can think of to run at those pressures on the street.
Tire pressure is a trade-off. In general, lower tire pressures give a smoother ride. That's because the tire is less stiff, so it acts like a shock absorber. However, the lower tire pressure also makes for more drag, as there is both a larger tire patch, and a limp tire actually eats energy as it flexes. At higher tire pressures, handling improves because the tire contact patch is more directly attached to the car. However, you get a stiffer ride. Since the tire is stiffer and the contact patch is smaller, your gas milage increases with higher tire pressure.
OK, so why not run the tires at 40 or 50 psi? The handling will be pretty good, to a point, and the ride will be pretty stiff. But there are problems with higher tire pressure. First, the contact patch of the tire will be pretty much just the center - the center of the tire will wear out quickly, and the outer parts of the tread will be unworn - basically, you'll use up the tires quickly.
Both under and over-inflation results in rapid tire wear.
OK, so why does Saab say 30 psi? Because that's what Saab has determined to be the optimal trade-off between handling, tire life, and ride comfort. Spring rates and bushing compliance are designed with those numbers in mind.
I personally prefer about 34 psi, as it seems to crispen up the handling without compromising the ride. Again, personal choice.
You should run at tire pressures around the recommended. I wouldn't go much lower than 28 psi, but that doesn't seem to be an issue. I would never go beyond 36 to 38 psi (cold) - not only will the ride be stiffer, but you're going to wear out the tires early. Look at the tire tread - you should see even wear across the tread. Overinflation will wear the center out prematurely. The increase in gas milage might be nice, but it'll never compensate for having to buy a set of tires that much sooner.
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