Why do front tires sometimes have different air pressure than rear tires.

Dear Car Talk

Dear Car Talk | May 01, 1993

Dear Tom and Ray:

Most of the cars I've owned have called for the same tire pressure, front and rear. But I've always wondered why the pressure couldn't be more closely related to the weight distribution of the car. For example, if 60 percent of the curb weight is over the front wheels, and 40 percent is over the rear wheels, why isn't the tire pressure similarly distributed?

TOM: Basically, Don, it's because Americans can't be bothered trying to remember two different tire pressures. We're busy people. We don't have room in our brains for such trivia.

RAY: And car manufacturers, recognizing this fact, have designed suspensions around a single tire pressure, so that the car's SUSPENSION already compensates for the weight distribution. This leaves us free to put 30 pounds of air in each tire, and spend our brain power worrying about more important things...like world peace, and programming our VCRs.

TOM: The tire engineers at Goodyear tell us that a few European and high performance cars do use a small pressure differential to squeeze that extra little bit of handling out of a car. By making slight variations in front and rear tire pressure, you can affect the amount of understeer and oversteer you get on some cars. But on most of the cars you and I drive, we'd never notice the difference.

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