The numbers and letters on the sidewall of a tire indicates the tire's specific size, performance and type. Numbers that begin with the letter "P" indicate that the tire is P-Metric and is intended for American passenger vehicles.
Tires with no letters at the beginning indicates that the tire is Euro metric. The series of three numbers immediately following the letter indicates the width of the tire, measured from sidewall to sidewall. The numbers directly after the slash refer to the tire's aspect ratio. The letter R indicates a radial tire, while the final numbers show the tire's wheel diameter.