General rule for tire pressure?

There is an exception here. I once bought a large trailer to tow behind an Expedition 4x4 EL (already a heavy vehicle). I could tell tires even inflated to the max were not right and got lots of sway. I bought new tires for the SUV (same size) but higher load range. The max pressure was something like 100 psi, the specs on the door were something around 40 psi. At max pressure these tires rode like they were solid steel even pulling an 8k lb trailer, so I played with the pressure a little. If memory serves me (about 5 yrs back) I used 80 on the rear for towing and 60 on the front. When not towing, I think I used 50 on all. I am sure there is a scientific way to get this right, but I will say when not towing, and lowering the psi to 50. I got a decent ride and the SUV handled far better in turns etc. btw, the TPMS will not work with higher range tires as it always senses tire is over inflated, Ford would not reset for me. So, I just manually checked tires often. I will say for anyone towing a heavy trailer, check out if you can get a higher load range tire for you tow vehicle. It makes a huge positive difference.