2004 GMC Savana Van Owner's Manual - Page 308

(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: The service description indicates the load range and speed rating of a tire. The load index can range from 1 to 279. Speed ratings range from "A" to "Z". The light truck tire size example above shows dual or single tire configurations. Light Truck (LT-Metric) Tire (A) Light Truck (LT-Metric) Tire: The United States version of a metric tire sizing system. The letter "LT" as the first two characters in the tire size means a light truck 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 illustration, it would mean that the tire's sidewall is 75% as high as it is wide. Tire Terminology and Definitions Air Pressure: The amount of air inside the tire pressing outward on each square inch of the tire. Air pressure is expressed in pounds per square inch (psi) or kilopascal (kPa). Accessory Weight: This means the combined weight of optional accessories. Some examples of optional accessories are, automatic transmission, power steering, power brakes, power windows, power seats, and air conditioning. Aspect Ratio: The relationship of a tire's height to its width. 5-62