2004 Pontiac GTO Owner's Manual - Page 245
2004 Pontiac GTO Manual
Page 245 highlights
Tire Size The following illustration shows an example of a typical passenger car tire size. (B) Tire Width: The three-digit number indicates the tire section width in millimeters from sidewall to sidewall. (C) Aspect Ratio: A two-digit number that indicates the tire height-to-width measurements. For example, if the tire size aspect ratio is "70," as shown in item "C" of the illustration, it would mean that the tire's sidewall is 70% as high as it is wide. (D) Construction Code: A letter code is used to indicate the type of ply construction in the tire. The letter "R" means radial ply construction; the letter "D" means diagonal or bias ply construction; and the letter "B" means belted-bias ply construction. (E) Rim Diameter: Diameter of the wheel in inches. (A) Passenger (P-Metric) Tire: The United States metric tire sizing system uses the letter "P" to designate a passenger vehicle tire. The European metric tire sizing system does not use the letter "P" to designate a passenger vehicle tire. (F) Service Description: These characters represent the load range and the speed rating of a tire. The load range represents the load carry capacity a tire is certified to carry. The speed rating is the maximum speed a tire is certified to carry a load. Speed ratings range from "A" to "Z". 5-55