Tire Terms

Tire Terms
Aspect Ratio	Section height/section width x 100 - ratio between tire height and width
Asymmetric	When opposite sides of a tire's tread pattern are not identical.
Backside Setting	The distance from the mounting surface of the wheel, which contacts the hub, to the back rim flange. It is sometimes referred to as the backspacing or backside measurement.
Balance	The even distribution of weight on a mounted wheel and tire.
Bias-Belted Tire	A passenger type tire which has two rubberized plies of cords which are crossed over one another at an angle (on a bias) plus two reinforced belts which encircle the tires under the tread.
Block Tread Design	A tire tread pattern made of raised rubber compound segments.
Bolt Circle	Sometimes referred to as bolt pattern: The number of lug holes on the diameter of the imaginary circle that each lug hole is centered on.
Carcass	The portion of a tire that is the foundation for the tread, belts, bead and sidewall.
Casing	The structure of tire cords locked around wire beads.
Compound	The general term referring to the chemical formula for the tread material.
Criss-Cross Torquing	The recommended sequential tightening of the lug nuts in a pattern across from one another to help ensure even tightening.
Grooves	Circumferential channels between and the tread ribs of a tire.
Hub Centric	A situation where the center bore of the wheel is made to match up with the diameter of the automobile hubs; the wheel is then balanced by the center hold rather that the lug holes.
Hydroplaning	Loss of traction at high speeds caused by a wedge of water that lifts a tire off the road surface.
Load Rating	The maximum weight that the tire is designed to carry; dictated by the tire's construction. Metric passenger type tires are offered with a Standard Load Rating (up to 35 psi), or Extra Load Rating (up to 41 psi). LT Metric (truck type) tires are offered with ply ratings of C (8 ply), D (8 ply), and (10 ply) and at various inflation pressures up to 80 psi.
Low Profile	A term describing a tire with a low relative aspect ratio or series classification (short sidewall, wide tread).
Negative Offset	A condition where the wheel's mounting surface is closer to the inside of the wheel; when the mounting surface is inboard the wheel's centerline.
Nominal Rim Diameter	Diameter of rim seat supporting the tire bead. Examples: 13', 15" and 16.5".
Offset	The positive or negative distance from the wheel's centerline to the mounting surface of the wheel.
Overall Diameter	The diameter of the inflated tire without any load.
Overall Width	Maximum width in cross-section of the unloaded tire including protruding sides ribs and decorations.
Ply	A layer of rubber-coated fabric or wire making up the tire casing.
Positive Offset	A condition where the wheel's mounting surface is closer to the street side of the wheel; when the mounting surface is outboard the wheel's centerline.
Radial Ply Tire	A type of tire that has one or more rubberized plies of cords running from bead to bead (at right angles to the tread and parallel to each other), plus two or more plies of reinforced belts which encircle the tire under the tread.
Ribs	Part of a tire tread pattern created by grooves that run circumferentially around the tire.
Rim Diameter	The distance between bead seat to bead seat at beat seat radius.
Rim Flange	The edge of the wheel's rim that the clip-on weights attach to.
Rim Width	The distance between the inside surfaces 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 and decorations).
Series	A numerical representation of a tire's aspect ratio; for example, 50 series.
Shoulder Blocks	Raised rubber compound segments on the part of the tire tread nearest the sidewall.
Sipes	Slits in the tire tread. Small cuts in the surface of the tread to improve traction.
Steel Belt	A belt material used in radial tires. Its high stiffness provides good handling and low treadwear.
Tire Profile	A term representing the portion of a tire measured as its aspect ratio or series.
Tread Blocks	Raised rubber compound segments on the outside visible part of a tire.
Tread Width	The portion of the tread design that comes in contact with the road.
Unsprung Weight	The total weight of the automobile's components not supported by the suspension system; wheels and tires are prime examples.
UTQG	Uniform Tire Quality Grade - A government-mandated tire rating system based on a tire's performance in treadwear durability, traction, and temperature resistance. UTQG ratings are branded on the tire's sidewall.
Varied-Pitch Ratio	Variations of angles and sizes of a tire's tread elements that reduce ride noise levels.
Zero Offset	A condition where the wheel's mounting surface coincides with the centerline of the wheel.