Air Pressure: The amount of air inside the tire pressing outward on
each square inch of tire, expressed in pounds per
square inch (psi).
Alignment: The state in which all wheels on a vehicle are pointed in
the optimum direction relative to one another.
All-Season Tires: Tires that are designed for use on dry and wet
pavement and also provide traction on snow and ice.
Aspect Ratio: The percentage relationship of a tires height to its
section width. The most common is 75, with the range
continuing downward (65, 60, etc.) to 35. Low aspect
ratio (or ‘series’) tires are also referred to as low
Balance: The state in which a tire and wheel spin with all their
weight distributed equally.
Bead: A round hoop of steel wires, wrapped or reinforced by
ply cords, that is shaped to fit the rim; it holds the tire
onto the rim.
Belt: A rubber-coated layer of cords that is located between
he plies and the tread. Cords may be made from steel,
fiberglass, rayon, nylon, polyester or other fabrics.
Casing: The tire body beneath the tread and sidewalls.
Cold Inflation The amount of air pressure in a tire, measured in
Pressure: pounds per square inch (psi), before a tire has built up
heat from driving.
Cord: The strands of fabric forming the plies or layers of the
tire. Cords may be made from steel, fiberglass, rayon,
nylon, polyester or other fabrics.
Contact Patch: The portion of the tread that makes contact with the
Friction: The force between the tires and the road surface that
causes the tire to grip the road.
Groove: The space between two adjacent tread ribs; also called
Highway Tires: Also called Summer tires; designed for wet- and
dry-weather driving, but not for use on snow and ice.
Hydroplaning: A floating effect caused by tires losing contact with a
surface covered with water.
Innerliner: The innermost layer of a tubeless tire. The innerliner
prevents air from permeating through the tire.
Load Index: An assigned number ranging from 0 to 279 that
corresponds to the load carrying capacity of a tire.
Maximum Inflation The maximum air pressure to which a cold tire may be
Pressure: inflated, and the number is found molded onto the
sidewall. It is often different than the vehicle
manufacturers recommended operating pressure.
Overall Diameter: The diameter of the inflated tire, without any load.
Overall Width: The distance between the outside of the two sidewalls,
including lettering and designs.
Plus-Sizing: An option allowing drivers to customize their vehicle by
mounting low-profile tires on wider rims of one or two
inches greater diameter, usually enhancing vehicle
appearance, handling and performance.
Ply: A rubber-coated layer of fabric containing cords that
run parallel to each other, extends from bead to bead
and goes between the innerliner and belts or tread.
Radial Ply 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. Often
referred to as wheel or wheel rim.
Rim Diameter: The diameter of a tire rim, given in nearest whole
numbers (e.g. 15 inches).
Rim Width: Distance between the two opposite inside edges of the
Rolling Resistance: The force required to keep a tire moving at a uniform
speed. The lower the rolling resistance, the less energy
needed to keep a tire moving.
Rotation: The changing of tires from front to rear or from side to
side on a vehicle according to a set pattern; it provides
Section Height: The height of a tire, measured from rim to the outer
Section Width: The distance between outside of sidewalls, not
including any lettering or designs.
Shoulder: The area of a tire where the tread and sidewall meet.
Sidewall: The portion of a tire between the tread and the bead.
Sipes: Special slits in a tread that improve traction when the
road surface is wet or has dust, dirt, sand, snow or
other material on it.
Size: The combination of tire width, construction type, aspect
ratio and rim size used in differentiating tires.
Skid: To slip or slide on the road when tires lose their rolling
Snow Tire: Often referred to as Winter tires, a special type of tire
with a tread and compound that gives better traction in
snow and other extreme winter conditions.
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.
Tire: A precisely engineered assembly of rubber, chemicals,
fabric and metal designed to provide traction and
cushion road shock and to carry a load under varying
Tire Information A metal or paper tag permanently affixed to a vehicle
Placard: that indicates the appropriate tire size and inflation
pressure for the vehicle, as well as rim size and load
Tread: That portion of a tire that comes into contact with the
road. It is distinguished by the design of its ribs and
Treadwear Narrow bands, sometimes called ‘wear bars’, that
Indicator: appear across the tread of the tire when only 2/32 inch
of tread remains.
Tread Width: The width of a tires tread.
Traction: The friction between the tires and the road surface, or
the amount of grip provided.
Uniform Tire A tire information system that provides consumers with
Quality Grading ratings for a tires traction (from AA to C) and for
(UTQG): temperature (from A to C). Tread wear is normally
rated from 60 to 620. Ratings are determined by tire
manufacturers using government-prescribed test
procedures and are molded into the sidewall of the
Wear Bars: See Treadwear Indicator.