(D) Construction Code: A letter code is used toindicate the type of ply construction in the tire. The letterR means radial ply construction; the letter D meansdiagonal or bias ply construction; and the letter B meansbelted-bias ply construction.(E) Rim Diameter: Diameter of the wheel in inches.(F) Service Description: These characters representthe load range and speed rating of the tire. The loadindex represents the load carry capacity a tire is certifiedto carry. The load index can range from 1 to 279.The speed rating is the maximum speed a tire is certifiedto carry a load. Speed ratings range from A to Z.Tire Terminology and DefinitionsAir Pressure: The amount of air inside the tire pressingoutward on each square inch of the tire. Air pressureis expressed in pounds per square inch (psi) orkilopascal (kPa).Accessory Weight: This means the combined weightof optional accessories. Some examples of optionalaccessories are, automatic transmission, power steering,power brakes, power windows, power seats, andair conditioning.Aspect Ratio: The relationship of a tire’s height toits width.Belt: A rubber coated layer of cords that is locatedbetween the plies and the tread. Cords may be madefrom steel or other reinforcing materials.Bead: The tire bead contains steel wires wrapped bysteel cords that hold the tire onto the rim.Bias Ply Tire: A pneumatic tire in which the plies arelaid at alternate angles less than 90 degrees to thecenterline of the tread.Cold Inflation Pressure: The amount of air pressurein a tire, measured in pounds per square inch (psi)or kilopascals (kPa) before a tire has built up heat fromdriving. See Inflation - Tire Pressure on page 5-58.Curb Weight: This means the weight of a motor vehiclewith standard and optional equipment including themaximum capacity of fuel, oil and coolant, but withoutpassengers and cargo.DOT Markings: A code molded into the sidewall of atire signifying that the tire is in compliance with theU.S. Department of Transportation (DOT) motor vehiclesafety standards. The DOT code includes the TireIdentification Number (TIN), an alphanumeric designatorwhich can also identify the tire manufacturer, productionplant, brand and date of production.GVWR: Gross Vehicle Weight Rating, see LoadingYour Vehicle on page 4-45.5-56
