wheel size measurement
The letter R in a tire size stands for Radial, which means the layers run radially across the tire. Wheel Diameter is the size of the wheel measured from one end to the other. It tells us the size of the wheel that the tire is intended to fit. A size P215/65 R15 tire is made for a wheel with a 15 diameter. Load Index indicates the maximum load that the tire can support when properly inflated.