(C) Aspect Ratio: A two-digit number thatindicates 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’ssidewall 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 letter R means radial ply construction;the letter D means diagonal or bias plyconstruction; and the letter B means belted-biasply construction.(E) Rim Diameter: Diameter of the wheel ininches.(F) Service Description: The service descriptionindicates the load range and speed rating of atire. The load index can range from 1 to 279.Speed ratings range from A to Z.Tire Terminology and DefinitionsAir Pressure: The amount of air inside thetire pressing outward on each square inch of thetire. Air pressure is expressed in poundsper square inch (psi) or kilopascal (kPa).Accessory Weight: This means the combinedweight of optional accessories. Some examples ofoptional accessories are, automatic transmission,power steering, power brakes, power windows,power seats, and air conditioning.Aspect Ratio: The relationship of a tire’s heightto its width.Belt: A rubber coated layer of cords that islocated between the plies and the tread. Cordsmay be made from steel or other reinforcingmaterials.Bead: The tire bead contains steel wires wrappedby steel cords that hold the tire onto the rim.Bias Ply Tire: A pneumatic tire in which the pliesare laid at alternate angles less than 90 degreesto the centerline of the tread.Cold Tire Pressure: The amount of air pressurein a tire, measured in pounds per square inch(psi) or kilopascals (kPa) before a tire has built upheat from driving. See Inflation - Tire Pressureon page 6-60.Curb Weight: The weight of a motor vehicle withstandard and optional equipment including themaximum capacity of fuel, oil, and coolant,but without passengers and cargo.6-57
