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first character in the tire size

means the tire is for temporary use only.

(7) TPC Spec (Tire Performance Criteria Specification) : Original equipment tires designed to GM's specific tire performance criteria have a TPC specification code

molded onto the sidewall. GM's

TPC specifications meet or exceed all federal safety guidelines.

Tire Designations

Tire Size

The following is an example of a

typical passenger vehicle tire size.


(1) Passenger (P-Metric) Tire : The United States version of a metric tire sizing system. The

letter P as the first character in


the tire size means a passenger vehicle tire engineered to

standards set by the U.S. Tire and Rim Association.

(2) Tire Width : The three-digit number indicates the tire section

width in millimeters from sidewall to sidewall.

(3) Aspect Ratio : A two-digit number that indicates the tire height-to-width measurements.

For example, if the tire size aspect ratio is 60, as shown in item 3 of

the illustration, it would mean that the tire's sidewall is

60 percent as high as it is wide.

(4) 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.

(5) Rim Diameter : Diameter of the wheel in inches.


(6) Service Description : These characters represent the load

index and speed rating of the tire. The load index represents the load carrying capacity a tire is certified to carry. The speed rating is the

maximum speed a tire is certified to carry a load.

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).

Accessory Weight : The combined weight of optional accessories.

Some examples of optional accessories are automatic

transmission, 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 between the plies and the tread. Cords may be made from steel or other reinforcing


Bead : The tire bead contains steel wires wrapped by steel cords that hold the tire onto the rim.

Bias Ply Tire : A pneumatic tire in which the plies are laid at

alternate angles less than

90 degrees to the centerline of the tread.

Cold Tire Pressure : The amount of air pressure in a tire, measured in kPa (kilopascal) or psi (pounds per square inch) before a tire has built up heat from driving. See

Tire Pressure 0 356.

Curb Weight : The weight of a motor vehicle with standard and

optional equipment including the maximum capacity of fuel, oil, and coolant, but without passengers

and cargo.


DOT Markings : A code molded into the sidewall of a tire

signifying that the tire is in compliance with the U.S.

Department of Transportation (DOT) Motor Vehicle Safety

Standards. The DOT code includes the Tire Identification Number

(TIN), an alphanumeric designator which can also identify the tire

manufacturer, production plant, brand, and date of production.

GVWR : Gross Vehicle Weight Rating. See Vehicle Load Limits 0 211.

GAWR FRT : Gross Axle Weight Rating for the front axle. See

Vehicle Load Limits 0 211.

GAWR RR : Gross Axle Weight Rating for the rear axle. See

Vehicle Load Limits 0 211.

Intended Outboard Sidewall :

The side of an asymmetrical tire that must always face outward

when mounted on a vehicle.


Kilopascal (kPa) : The metric unit for air pressure.

Light Truck (LT-Metric) Tire : A tire used on light duty trucks and some multipurpose passenger


Load Index : An assigned number ranging from 1 to 279 that

corresponds to the load carrying capacity of a tire.

Maximum Inflation Pressure :

The maximum air pressure to

which a cold tire can be inflated.

The maximum air pressure is molded onto the sidewall.

Maximum Load Rating : The load rating for a tire at the maximum

permissible inflation pressure for that tire.

Maximum Loaded Vehicle

Weight : The sum of curb weight, accessory weight, vehicle capacity weight, and production options




Normal Occupant Weight : The number of occupants a vehicle is designed to seat multiplied by

68 kg (150 lb). See Vehicle Load Limits 0 211.

Occupant Distribution :

Designated seating positions.

Outward Facing Sidewall : The side of an asymmetrical tire that has a particular side that faces

outward when mounted on a

vehicle. The side of the tire that

contains a whitewall, bears white lettering, or bears manufacturer, brand, and/or model name

molding that is higher or deeper than the same moldings on the other sidewall of the tire.

Passenger (P-Metric) Tire : A tire used on passenger cars and some

light duty trucks and multipurpose vehicles.

Recommended Inflation

Pressure : Vehicle manufacturer's recommended tire inflation

pressure as shown on the tire



See Tire Pressure 0 356 and Vehicle Load Limits 0 211.

Radial Ply Tire : A pneumatic tire in which the ply cords that extend to the beads are laid at 90 degrees to the centerline of the tread.

Rim : A metal support for a tire

and upon which the tire beads are seated.

Sidewall : The portion of a tire between the tread and the bead.

Speed Rating : An alphanumeric code assigned to a tire indicating the maximum speed at which a

tire can operate.

Traction : The friction between

the tire and the road surface. The amount of grip provided.

Tread : The portion of a tire that comes into contact with the road.

Treadwear Indicators : Narrow bands, sometimes called wear

bars, that show across the tread of


a tire when only 1.6 mm (1/16 in) of tread remains. See When It Is

Time for New Tires 0 363.

UTQGS (Uniform Tire Quality Grading Standards) : A tire

information system that provides consumers with ratings for a tire's traction, temperature, and

treadwear. Ratings are determined by tire manufacturers using

government testing procedures. The ratings are molded into the sidewall of the tire. See Uniform Tire Quality Grading 0 365.

Vehicle Capacity Weight : The number of designated seating

positions multiplied by

68 kg (150 lb) plus the rated cargo

load. See Vehicle Load Limits 0 211.

Vehicle Maximum Load on the Tire : Load on an individual tire due to curb weight, accessory

weight, occupant weight, and cargo weight.