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Performance Tires - Tire Anatomy 101

The Inside Story On Performance Tires

Glossary
Aspect Ratio: The relationship of a tire's height to its width, expressed as a number that represents the nominal percent the tire's height is of its width.

Bead: A round hoop of steel wires that is shaped to fit the rim around which the tire's body plies are wrapped and holds the tire onto the rim.

Belt: A rubber-coated layer of cords that is located between the body plies and the tread rubber. Cords may be made from steel, fiberglass, rayon, nylon, polyester, or other fabrics.

Bias-Ply Tire: A pneumatic tire in which the plies are laid at alternate angles less than 90 degrees to the center line of the tread. Plies usually run at angles of about 30-40 degrees relative to the tire center line in a criss-cross fashion.

Carcass: The tire body beneath the tread and sidewalls; also called the casing.

Cold Inflation Pressure: The amount of air pressure in a tire, measured at ambient temperature before a tire has built up heat from driving.

Compound: The hardness or softness of the rubber used in tire construction.

Cord: The strands of material forming the body plies or belt plies of the tire. Cords may be made from aramid, fiberglass, rayon, nylon, polyester or steel.

DOT Markings: A code molded into the sidewall of a tire signifying that the tire complies with U.S. Department of Transportation safety standards. The DOT code includes an alphanumeric designator that can also identify the tire's manufacturer, production plant, date of production, and brand.

Footprint: That portion of the tread in contact with the road.

High-Performance Tire: In the tire industry, those tires with speed ratings of S or greater and aspect ratios of 70 or less.

Highway Tires: Also called summer tires; designed for wet-and-dry weather driving, but not for use on snow and ice.

Hydroplaning: A skimming effect caused by tires losing contact with a surface covered with water when traveling at speed.

Innerliner: The innermost layer of a tubeless tire. The innerliner prevents air from permeating through the tire.

Overall Diameter: The outside diameter of the inflated tire, without any load.

Overall Width: The distance between the outside of the two sidewalls, including lettering and designs.

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