Follow the tire manufacturer's spec (not the max rating, but the actual load range chart), and adjust to your riding style. The range listed in the manual will get you in the ball park of most road tires if you want to be safe. In general, a little less psi = more traction and slower turn-in, but reduced mileage. Spec psi = less traction but maximum mileage and a potential rougher ride. When your tires have an evenly scrubbed look across the entire contact area, you are at the right psi for your bike and weight. If the worn area looks splotchy, reduce pressure slightly until it all looks the same. If the handling starts to feel sluggish or sloppy, increase tire pressure.