Back when I had a Jeep (lifted, big tires, etc) the guys I went offroading with showed me a trick for figuring out the proper tire pressure. When you put non-OEM size tires on a car you can no longer rely completely on the OEM specifications for pressure. The reality is that the ideal pressure it the point at which the entirety the tread (side to side) is on the road while you're driving, no more, no less. This ensures that the sidewalls will be flexed appropriately and that your tread will wear evenly.

Start by eye-balling it. Inflate the tires to the point that it looks about like all the tread is touching the ground. Then, draw a line with chalk across the tread. Drive a few feet in a straight line so that the line gets worn off.

If you still see chalk on the edges of the tread, you've got too much pressure. If you see no chalk, up the pressure a little bit until you do (it's an iterative test) and then come back down to just below where you see chalk.

This ensures that your contact patch uses the entirety of the tread on the tire, which guarantees even wear and longer life. It can also be helpful in diagnosing a camber issue if you see chalk on just one side of the tire tread but not the other.

Generally speaking when you're using OEM size tires on a car, though, you can count on the pressure recommendations in the doorjamb to be correct, but if you want to test it yourself, the chalk method is a cheap, easy way to do so.