Running pressure that is too high will give you a rougher ride and wear out the centre quicker. To determine the optimal tire pressure for a given tire and load, use the chalk line method as follows:
1) Fill the tires to some arbitrarily high pressure (38 psi is good),
2) draw a straight line across the tread of each of the tires (perpendicular to the sidewall),
3) drive in a straight line for ~ 100 feet,
4) examine the chalk lines.
If the line is gone only in the middle, the tire is overinflated. Reduce air pressure a couple of psi and try again.
If the line is gone only near the edges, the tire is underinflated. Add air and repeat process.
If the line is gone altogether, the inflation is good for the load in the vehicle. Write the numbers down for future reference.
