320 VEHICLE CARE(1) Passenger (P-Metric) Tire :The United States version of ametric tire sizing system. Theletter “P” as the first character inthe tire size means a passengervehicle tire engineered tostandards set by the U.S. Tire andRim Association.(2) Tire Width : The three-digitnumber indicates the tire sectionwidth in millimeters from sidewallto sidewall.(3) Aspect Ratio : A two-digitnumber that indicates the tireheight-to-width measurements.For example, if the tire size aspectratio is 60, as shown in item (3) ofthe illustration, it would meanthat the tire's sidewall is60 percent as high as it is wide.(4) Construction Code : A lettercode is used to indicate the typeof ply construction in the tire. Theletter “R” means radial plyconstruction; the letter “D” meansdiagonal or bias ply construction.(5) Rim Diameter : Diameter ofthe wheel in inches.(6) Service Description : Thesecharacters represent the loadindex and speed rating of the tire.The load index represents the loadcarrying capacity a tire is certifiedto carry. The speed rating is themaximum speed a tire is certifiedto carry a load.Tire Terminology andDefinitionsAir Pressure : The amount of airinside the tire pressing outwardon each square inch of the tire.Air pressure is expressed in kPa(kilopascal) or psi (pounds persquare inch).Accessory Weight : The combinedweight of optional accessories.Some examples of optionalaccessories are automatictransmission, power windows,power seats, and air conditioning.Aspect Ratio : The relationship ofa tire's height to its width.Belt : A rubber coated layer ofcords between the plies and thetread. Cords may be made fromsteel or other reinforcingmaterials.Bead : The tire bead contains steelwires wrapped by steel cords thathold the tire onto the rim.Bias Ply Tire : A pneumatic tire inwhich the plies are laid atalternate angles less than90 degrees to the centerline of thetread.Cold Tire Pressure : The amountof air pressure in a tire, measuredin kPa (kilopascal) or psi (poundsper square inch) before a tire hasbuilt up heat from driving. SeeTire Pressure 0 322.Curb Weight : The weight of amotor vehicle with standard andoptional equipment including the
