Tire Glossary

BEAD:
The part of the tire that is constructed to hold the tire securely to the rim. It is made of high tensile steel wires wrapped in woven fabric and secured within the ply ends.

BELT:
Narrow strips of fabric, fiberglass or steel cords running in a circumferential direction immediately under the tread in the crown of a tire (between the tread and casing plies). They constrict the plies to provide the tire with high lateral stiffness, and act to help the tire resist deformation in its footprint, and thus give more effective braking and traction. The belts also protect the air chamber against punctures.

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

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 which can also identify the tire's manufacturer, production plant, date of production and brand.

GROOVE:
The space between two adjacent tread ribs or blocks; also called tread grooves.

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

ORIGINAL TREAD DEPTH (OTD):
Original Tread Depth (OTD) is the tread depth of a new tire measured at the point one-fourth the width of the tire crown section from the crown center.

OUT-OF-ROUND:
A condition where the tire is not round to within standards due to an uneven distribution of rubber, improper molding, etc.

ROTATION:
The changing of tires from front to rear or from side-to-side on a vehicle according to a set pattern to achieve even tread wear.

SECTION HEIGHT:
The height of the tire, measured from rim to the outer tread.

SECTION WIDTH:
Maximum width of the tire not including any lettering or designs.

SHOULDER:
The area of a tire where the tread and sidewall meet. Also called tread.

SIDEWALL:
That portion of a tire between the tread and bead.

SIPES:
Special slits within a tread block that increase wet and snow traction. Sipes provide more biting edges and allow for the dispersion of water from under the tread surface.

TIRE PLACARD:
A metal or paper tag permanently affixed to a vehicle which indicates the appropriate tire size and inflation pressures for the vehicle.

TREAD RIB:
The tread section usually composed of many tread blocks that runs around the circumference of the tire, separated by the circumferential tread grooves.

TREAD DEPTH:
The distance between the surface of the tread and the bottom of the groove of a tire. It is usually measured at a few points located halfway between the centerline and the edge of the tread.

TREADWEAR INDICATOR:
Narrow bands, sometimes called "wear bars," that appear across the tread surface of the tire when only 2/32 inch of tread remains.

TIRE SIZE:
The size of each tire is indicated by nominal width and rim diameter in inches and millimeters. Radial structure is indicated by the letter "R". For some tires the aspect ratio is indicated by a percentage.