I use chalk to help determine the correct tire pressure, record that psi number and use it to check and set that pressure from then on. I simply scrub the chalk across the tread of the tire in a one inch wide band from side to side on the tread, drive the car forward 40 or 50 feet and see where the chalk has been rubbed off, middle, outside edges or evenly. I adjust the tire pressure to get a full even scrub of the chalk off the tread. That is the tire pressure I need for that tire with that load on it. Period.

I generally run 32 up front and 18 in the rears to get them to the correct shape. Other factors such as spirited driving at higher speeds sometimes force me to increase rear tire pressure a couple of pounds to help stiffen the tire flex out back.