Vehicle weight is a consideration, yes, but once you start changing width and sidewall aspect a lot changes like carcass stiffness, etc so correct pressure for one tire will be different than another type on the same vehicle. I'll agree that a PSI or two either way doesn't make that much difference usually, but it's ignorant just to blindly fill them based on rules of thumb for some generic car. Take a look at the owners manual for a car that comes with 2 or 3 different wheel sizes, and most likely you'll see 2 or 3 different tire pressures. It really depends on what you want to get out of your tires, performance, even tread wear, etc.

ALso, max pressure can vary from tire model to tire model, so just going "(whatever) PSI under max" doesn't really work. You'll probably have no tread left in the center of the contact patch fairly soon if you follow that advice..

 

ok, good rule of thumb when a car run 32 psi when truck or suv run 35 of you have lots of weight in the car or truck you sould do as followed, car 35-36 and truck 38-40 depending on how much weight- work at NTB for 2 years and that is the rule that we always follow, hope this helps