Quote:
Originally posted by Pragma
I agree with shakran: the pressures written on the tire itself are the recommended values from the factory, but the ones on your door are the correct values - if in doubt, read your car's manual. The car manufacturer knows what pressure tires the car is supposed to have.
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Okay, lets take this into a hypathecial sistuation. I have a 98 Camaro Z-28 w/o the Z rated tire option. This means it comes with factory H rated tires, RSA's in most cases. The tire pressure that would be listed inside the door is 32PSI for all four corners. The pressure listed on the tires would be 32PSI - everything is fine and dandy. Now after I demolish this set of tires I go off and purchase a set of P-Zero's (Z-rated) tires. These say on the tire that I should run them at 45PSI, the door still reads 32PSI. Now if you run them at 45PSI the tire will maintain the proper sidewall profile and the tire will keep the correct footprint on the road. If I run the manufatures suggestions at 32PSI the tire will be like driving on a marshmellow. With 32PSI the sidewalls will buldge, the footprint will be huge and there would be a increased risk of dislodging a tire during a emergency driving manuver. It will also add stress to the sidewall increasing the breaking down of the sidewall on the tire. You will have extreme wear on the outside edges of the tire but still have an almost new tire on the middle of the tread patch. These are all things that are proven charateristics of a tire being under inflated. This is a thing that could get played out at any time and shows just how imparative it is to follow the tire manufatures suggested inflation values.
Back on topic - IN THE GM MANUAL (1995 firebird owners manual)it states that "you should ALWAYS follow the tire manufatures suggested inflation rates."
Edit- at was brought up, usually a tire lists the maxium tire pressure but in information you recived when you bought tires, it lists usually the maxium and then suggested tire pressured dependent on vehical weight. These are the numbers that you should use as a base line. These are going to be much more accurate than the factory specs. There is never a "perfect" way to figure out what tire pressures you should run. There are hundreds of factors that will change how you should setup your cars tires. Atleast with a weight table published by the tire manufature they know how the footprint will be effected by a differnce in tire pressure as well as warning off any increased tire wear due to improper inflation.
Look at this from the other direction, the car manufature doesn't take into account differnt profile or speed ratings on the tires.