(A) Light Truck (LT-Metric) Tire: The United Statesversion of a metric tire sizing system. The letters LT asthe first two characters in the tire size means a lighttruck tire engineered to standards set by the U.S. Tireand Rim Association.(B) Tire Width: The three-digit number indicates thetire section width in millimeters from sidewall to sidewall.(C) Aspect Ratio: A two-digit number that indicatesthe tire height-to-width measurements. For example, ifthe tire size aspect ratio is 75, as shown in item C of thelight truck (LT-Metric) tire illustration, it would meanthat the tire’s sidewall is 75% as high as it is wide.(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: The service descriptionindicates the load range and speed rating of a tire. Theload index can range from 1 to 279. Speed ratingsrange 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, and airconditioning.Aspect Ratio: The relationship of a tire’s height to itswidth.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 pressure ina tire, measured in pounds per square inch (psi) orkilopascals (kPa) before a tire has built up heatfrom driving. See Inflation - Tire Pressure on page 5-67.5-64
