2012 GMC Sierra Owner's Manual - Page 440

10-54 Vehicle Care would mean that the tire's sidewall is 75 percent 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. (F) Service Description: These characters represent the load index and speed rating of the tire. The load index represents the load carrying capacity a tire is certified to carry. The speed rating is the maximum speed a tire is certified to carry a load. (F) Tire Ply Material : The type of cord and number of plies in the sidewall and under the tread. (G) Single Tire Maximum Load: Maximum load that can be carried and the maximum pressure needed to support that load when used as a single. For information on recommended tire pressure see Tire Pressure on page 10‑58 and Vehicle Load Limits on page 9‑16. Passenger (P‐Metric) Tire Tire Designations Tire Size The examples show a typical passenger vehicle and light truck tire size. (A) Passenger (P‐Metric) Tire: The United States version of a metric tire sizing system. The letter P as the first character in the tire size means a passenger vehicle tire engineered to standards set by the U.S. Tire and Rim Association. (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 75, as shown in item C of the tire illustration, it