You can also determine what your tire pressure should be. It takes some time, a compressor or air tank, some chalk and a flat place to drive.
Find a flat smooth surface to drive in a straight line. A parking lot would work.
Wipe a section of tire tread clean. Then use the chalk to cover the tread from side to side. Add a chalk mark on the sidewall to point to the tread.
Drive in a straight line for a distance. Stop around 60 ft or so.
Observe the chalk on the tread.
If it's evenly worn, the tire pressure is good. Write down the new pressure number.
If it's worn on the edge more than the center, add some air to the tire and recheck.
If it's worn in the center more than the edge, reduce the air pressure and recheck.
For best wear, highway traction and performance, having the tread in good contact with the highway is best. Regardless of what the recommended pressure is from the manufacturer, you can determine your best pressure for your vehicle. If you changed the size tires ("what's the biggest tire I can fit?"), carry tools, etc. then you have change the contact patch and weight of the vehicle. It takes some time to do. This will allow your tires to wear evenly saving some money. It keeps the tires in even contact with the highway to maximize braking performance.
