Ok here is what any tire guy worth a dump, will tell you. As long as your tires are wearing evenly across then you are running them at the perfect air pressure. Now with that being said the manufacturer says to run your fronts at about 5lbs higher then the rears because it helps to prevent cupping. This has alot to do with the weight of the engine and the way the caster/camber has the tires riding on the road. Sometimes you can bump them up a few pounds in order to get better fuel milleage but you will probably start wearing your tires out in the centers if you do this. The tire manufacturers only put a max tire pressure on there because if you run them higher then that then you are taking a chance on blowing the tire. Another thing is that if you run the tire too low you run a chance on heating the sidewalls up and that can cause seperation and yet again a blowout. so back to the beggining. If you are wearing your tires out evenly then you are running the correct tire pressure. If you are planning on hauling a large load then bump them up accordingly but with load range E tires (10 ply) then do not go above 80 psi. with load range D (8 ply) then do not go above 55 psi. I believe it is.
