2011 Chevrolet Silverado 1500 Regular Cab Owner's Manual - Page 466

10-60 Vehicle Care (E) Rim Diameter : Diameter of the wheel in inches. (F) Load Range : Load Range. (G) Service Description: The service description indicates the load index and speed rating of a tire. If two numbers are given as in the example, 120/116, then this represents the load index for single versus dual wheel usage (single/dual). The speed rating is the maximum speed a tire is certified to carry a load. Accessory Weight: 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. Belt: A rubber coated layer of cords that is located between the plies and the tread. Cords may be made from steel or other reinforcing materials. Bead: The tire bead contains steel wires wrapped by steel cords that hold the tire onto the rim. (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 light truck (LT‐Metric) tire illustration, it 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. 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 kPa (kilopascal) or psi (pounds per square inch).