Other options would be no P indicating metric sizing, or LT for light truck. LT truck tires are designed for heavier loads and more rugged conditions. Width of the tire in millimeters . Aspect ratio . The height of the sidewall section compared to the width of the tire.
R indicates radial construction.
Wheel Size Designation . This indicates the distance across the center hole of a tire. You must match wheel diameter and the tire opening. That number stands for a specific weight carrying capability. The key is that the higher the number, the greater load carrying capacity.