Tire Terminology and Definitions

Air Pressure: The amount of air inside the tire pushing outward on the tire. Air pressure is expressed in kilopascals (kPa) or pounds per square inch (psi).

Accessory Weight: The total weight of optional accessories. Some examples of optional accessories are automatic transmission, power seats and air conditioning.

Aspect Ratio: The ratio of the tire height to its width.

Belt: A rubber-coated cord layer located between the plies and the tread. Cords may be made of steel or other reinforcing materials.

Bead: The tire bead consists of steel wires wrapped with steel cords that hold the tire on the rim.

Bias Ply Tire: A pneumatic tire in which the plies are laid at alternating angles of less than 90 degrees to the centerline of the tread.

Cold Tire Pressure: The air pressure in the tire, measured in kilopascals (kPa) or pounds per square inch (psi) before the tire warms up from driving.

Curb Weight: The weight of the vehicle with standard and optional equipment, with maximum fuel, oil and coolant, but without passengers and cargo.

DOT Marking: The DOT code includes the Tire Identification Number (TIN), an alphanumeric designation that may also identify the tire manufacturer, manufacturing plant, brand and date of manufacture.

GVWR: gross vehicle weight rating.

GAWR FRT: Gross Axle Weight Rating, front axle.

GAWR RR: Gross Axle Weight Rating, rear axle.

Intended Outboard Sidewall: The side of an asymmetric tire that must always face outward when mounted on the vehicle.

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

Light Truck Tire (LT): A tire designated by the manufacturer as intended primarily for use on light trucks or multipurpose passenger vehicles.

Load Index: An assigned number in the range from 1 to 279 that corresponds to the load capacity of the tire.

Load Rating: The maximum load that the tire is designed to carry at the specified inflation pressure.

Maximum Inflation Pressure: The maximum air pressure to which a cold tire may be inflated. The maximum air pressure is molded on the sidewall.

Maximum Load Rating: The load rating of the 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 weight.

Normal Occupant Weight: The number of occupants the vehicle is designed to seat, multiplied by 68 kg (150 lbs).

Occupant Distribution: Designated seating positions.

Outboard Sidewall: The side of an asymmetrical tire that must face outward when mounted on the vehicle. The outboard sidewall carries white lettering or manufacturer, brand, and/or model name markings that are raised or recessed further than the same moldings on the inboard sidewall.

P-Metric Tire: A tire used on passenger cars and some light trucks and multipurpose vehicles.

Ply: A layer of parallel cords coated with rubber.

Pneumatic Tire: A mechanical device made of rubber, chemicals, fabric, and steel or other materials that, when mounted on a wheel, provides traction and contains gas or fluid that supports the load.

Production Options Weight: The total weight of installed standard production options exceeding 2.3 kg (5 lbs) over the standard items they replace, not previously included in curb weight or accessory weight, including heavy-duty brakes, ride height levelers, roof rack, heavy-duty battery, and special trim.

Recommended Tire Inflation Pressure: The tire inflation pressure recommended by the vehicle manufacturer and shown on the tire placard.

Radial Tire: A pneumatic tire in which the cord plies extend to the beads and are laid at 90 degrees to the centerline of the tread.

Wheel Rim: A metal support for the tire on 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 the tire can carry a load.

Traction: The friction between the tire and the road surface. The amount of traction provided.

Tread: The portion of the tire that contacts the road.

Tread Wear Indicators: Narrow bands, sometimes called wear bars, molded into the tread grooves that appear when only 1/16 inch of tread remains.

UTQGS: Uniform Tire Quality Grading Standards, an information system for tires that provides consumers with ratings for traction, temperature, and treadwear. Ratings are determined by the tire manufacturers using government-specified test procedures. The ratings are molded on the tire sidewall.

Vehicle Capacity Weight: The number of designated seating positions multiplied by 68 kg (150 lbs), plus the rated cargo and luggage load.

Maximum Vehicle Load on Tire: The load on an individual tire due to curb weight and accessory weight, plus maximum occupant and cargo weight.

Normal Vehicle Load on Tire: The load on an individual tire determined by distributing to each axle its share of the curb weight, accessory weight, and normal occupant weight, and driving on 2 wheels.

Vehicle Placard: A label permanently attached to the vehicle showing the original equipment tire size and recommended tire inflation pressure.