Air Pressure:
The amount of air inside the tire pressing outward on each square inch of tire; expressed in pounds per square inch (psi).
Alphanumeric:
A term for describing the size of a tire in which both letters of the alphabet and numbers are used.
Aramid:
A synthetic fabric used in some tires that is (pound-for-pound) stronger than steel.
Aspect Ratio:
The relationship of a tire's height to its width, expressed as a percent (%).
Bead:
A round hoop of steel wires, wrapped or reinforced by ply cords, that is shaped to fit the rim; holds the tire onto the rim.
Belted Bias Tire:
A pneumatic tire with a body similar to that of bias tires, but which also includes two or more belts under the tread.
Belt:
A special rubber-coated layer (or ply) of cords running circumferentially around the tire, located between the body plies and the tread. The cords may be made from steel, fiberglass, rayon, nylon, Kevlar, polyester or other fabrics.
They are designed to reinforce body plies to hold the tread flat on the road. Belts reduce squirm to improve tread wear and resist damage from impacts and penetration.
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 about 30-40 degrees to the center line in a crisscross fashion.
Carcass:
AKA Casing. The main body of the tire, beneath the tread and sidewalls, consisting of wire beads and body plies. It forms the foundation for the tread and sidewalls.
Cold Inflation Pressure:
The amount of air pressure in a tire, measured in pounds per square inch (psi) before a tire has built up heat from driving.
Compound:
The general term referring to the chemical formula for the tread material.
Cord:
The strands of fabric forming the plies or layers of the tire. Cords may be made from fiberglass, rayon, nylon, polyester, Kevlar or steel.
DOT Markings:
A code molded into the sidewall of a tire signifying that the tire complies with U.S. Department of Transportation motor vehicle safety standards. The DOT code includes an alphanumeric designator which can also identify the tire's manufacturer, production plant, date of production and brand.
Footprint:
AKA Contact Patch. That portion of the tread that contacts the road.
Groove:
The space between two adjacent tread ribs; also called tread grooves.
Inner liner:
A layer of specially compounded rubber forming the innermost layer of a tubeless tire, designed to inhibit loss of air pressure.
Loaded section height:
The height of the section of the tire that is making contact with the road.
Load Index:
An assigned number ranging from 0 to 279 that corresponds to the load carrying capacity of a tire.
Maximum Inflation Pressure:
The maximum air pressure to which a cold tire may be inflated; found molded onto the sidewall.
Nominal rim diameter:
The diameter of a tire rim.
Overall diameter:
The diameter of the inflated tire, mounted on the approved width rim, without any load.
Overall width:
The distance between the outside of the two sidewalls, including lettering and designs.
P-Metric:
Uniform designation of tire sizes, in metric measurements originally introduced by American tire manufacturers in 1977; commonly called "P-metric series." A typical P-metric tire is P205/70R14 93S.
Ply:
A layer of heat and impact resistant rubber-coated fabric containing cords that run parallel to each other; extends from bead to bead and goes between the inner liner and belts or tread; used to form the body of the tire. Automobile and light truck tire plies are normally constructed of nylon or polyester cords.
Radial Tire:
A type of tire with plies arranged so cords in the body run at 90 degree angles to the center line of the tread.
Rim:
A metal support for a tubeless tire or a tire and tube assembly upon which the tire beads are seated.
Rim width:
Distance between the two opposite inside edges of the rim flanges.
Section height:
The distance from rim seat to outer tread surface of an unloaded tire.
Section width:
The linear distance between the outside sidewalls of an inflated tire without any load (exclusive of protruding side ribs, raised lettering and decorations).
Series:
A numerical representation of a tire's aspect ratio; for example, 50 series Tires with the same aspect ratio, or relationship of height to width, are said to be the same “series”.
Shoulder:
The area of a tire where the tread and sidewall meet.
Shoulder Blocks:
Raised rubber compound segments on the part of the tire tread nearest the sidewall.
Sidewall:
That portion of a tire between the tread and the bead.
Sipes:
Special slits within a tread that increase wet and snow traction.
Siping:
The process of introducing sipes (or slits) into the tread.
Size:
The combination of tire width, construction type, aspect ratio and rim size used in differentiating tires.
Speed Rating:
An alphabetical code (A-Z) assigned to a tire indicating the range of speeds at which the tire can carry a load under specified service conditions.
Steel Belt:
A belt material used in radial tires. Its high stiffness provides good handling and low tread wear.
Tire:
A precisely engineered assembly of rubber, chemicals, fabric and metal designed to provide traction, cushion road shock and carry a load under varying conditions.
Tire Designation:
An alphanumeric code molded into the sidewall of the tire that describes the tire's size, including width, aspect ratio, rim diameter, load index and speed rating. Most designations use the P-Metric system.
Tread:
That portion of a tire that comes into contact with the road. It is distinguished by the design of its ribs and grooves.
Tread Blocks:
Raised rubber compound segments on the outside visible part of a tire.
Tread Rib:
The tread section that runs around the circumference of the tire, separated by the tread grooves.
Tread wear Indicator:
Narrow bands, sometimes called "wear bars," that appear across the tread of the tire when only 2/32 inch of tread remains.
Tread width:
The width of a tire's tread that comes in contact with the road.
Traction:
The friction between the tires and the road surface; the amount of grip provided.
UTQGS:
(Uniform Tire Quality Grading Standards) A tire information system that provides consumers with ratings (from A to C) for a tire's traction and temperature. Tread wear is normally rated from 60 to 620. Ratings are determined by tire manufacturers using government-prescribed test procedures, and are moulded into the sidewall of the tire.
Valve:
A device that lets air in or out of a tire. Fitted with a valve cap to keep out dirt and moisture and a valve core to prevent air from escaping.
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