2000 SE Tire pressure question

The info on the door jam says that cold air pressure should be 30 psi. The tires I have say 51 psi max air pressure. I usually check the pressures once per week. I air them up to about 40 psi and they look fine. If I was to take them down to 30 psi as recommended by GM, the tires look very low. Am I hurting the tires by going up to 40?

I believe the door tag would be for the stock GM tires, Good Year RS's.

Go by the tire label is your best bet.

That max load would be like during the summer.
You might have 35psi then you drive down blacktop that's 110deg, your tire gets hot building more pressure I've seen 65-70psi on a hot tire.
That's why they say to check them cold.

Try it sometime, check them cold then drive around for a while, you'll see the pressure rise higher(maybe not so much in the winter).

I keep mine around 35psi, I might drop it to 32psi in July-August for better grip. A low tire though can make your MPG drop.