Re: Mustang 1997 Coup 3.8 V6
FEAnt is right. I worked in a tire/mechanic shop for five years and we had people coming in with this idea frequently. The tire manufacturer prints a MAXIMUM pressure on the tire, something you should not exceed. running below this is fine. In fact, on many vehicles (excluding heavy duty trucks that run 80 psi, which is the max printed on 10 ply tires, which those vehicles call for) if you run the amount listed on the tire you will wear out the center of the tread faster than the rest because the extra pressure bows out the tire, allowing it to mostly run on just the inside tread. The opposite applies to underinflated tires, where the center tread can actually begin bowing upwards off the ground, and the outsides of the tire wear faster.
Whoever sold those passenger tires to the guy with the F250 wasn't doing his job correctly. You should always have tires rated for at least the pressure that the vehicle manufacturer calls for.