I think if you put a vehicle manufacturer and a tire manufacturer in the same room and ask them what pressure should you use, you will cause a fight between the two. I have dealt with both and each one tells me their theory is right. The vehicle manufacture tells me they have tested their vehicle to find the proper pressure to use and the tire manufacture tells me they have tested the tires for the proper pressure to use for their tire. To me there are a lot of variables to deal with. Tire wear, Are your tires wearing on the outside edges or in the middle of the tread? Outside wear indicates low pressure. Middle tread wear indicates too much pressure. Handling, Does your vehicle ride feel mushy or does it feel so hard it feels there is no suspension on the vehicle? If it feels mushy you probably have low pressure. If it feels hard you have too much pressure. Hot tires, Are your tires hot? If yes and you are not overloading them it would generally indicate low pressure from my experience from the flexing of the tire as it rolls. Those are just a couple of the variables without getting into toe in/toe out, cast, camber, loose or worn out ball joints/tie rod ends and other things that may cause problems. Springs rated for the load to be hauled make a big difference also. You don't want springs rated for a 10,000 pound load just to pull 500 pounds around. You also don't want springs rated for 500 pounds to pull 10,000 pounds around.
