Camber
The angle between the centerline of the tyre and a vertical line as viewed from the front.

Camber Thrust
A cornering force generated by the tyre's camber.

Casing
The tyre body composed of plies that form the tyre's structure and give it shape. Sometimes called the carcass.

Caster
The angle between the vehicle's steering axis and a vertical line, as viewed from the side.

Compounding
The combining of five basic ingredients: rubber, carbon black, plasticizers, curing materials, and ozone retardants to form the tread and other "rubber" components of a tyre.

Cornering Force
The lateral frictional force generated by a cornering tyre, acting in opposition to the centrifugal force.

Crown
The center area of a tyre's tread.

Deflection
The difference between a tyre's unloaded or free radius and the loaded radius.

Directional Stability
The tendency for a tyre to roll in its steered direction rather than follow road contours.

Footprint
The area of the tyre's tread that is in actual contact with the ground.

Harmonic Marking
Markings on wheels and tyres that allow match mounting to cancel tyre and wheel run out, minimizing vibration.

Hoop Strength
The retention strength inherent in the belt construction of a tyre that resists centrifugal force and provides dimensional stability.

Hydroplaning
The accumulation of water in a film under the footprint that causes a tyre to lift from the road surface, losing traction. Hydroplaning is affected by vehicle speed; tread pattern, and water depth.

Imbalance
The condition that exists when a tyre's mass is not evenly distributed around the rolling axis and centerline, causing bounce (static imbalance) or shake (dynamic imbalance).

Inflation Pressure
The pressure of air inside a tyre that applies a tensile stress to the tyre cords, permitting them to carry the vehicle's load.

Liner or Inner-Liner
The thin layer of halo butyl rubber inside a tyre that contains the inflation air, sometimes called the inner-liner. All tubeless tyres are manufactured with an inner-liner.

Mixing Tires
Fitting tyres of different sizes or constructions to a vehicle. Mixing should be avoided. Some performance vehicles, however, specify different size tyres on front and rear axles.

Mounting Tires
The act of fitting tyres to wheel rims.

Overall Diameter
The diameter of an unloaded, inflated tyre measured from the crown on one side to the crown on the opposite side. The free radius equals one-half the overall diameter. Sometimes called the outside diameter.

Over Inflation
The condition that exists when a tyre is inflated beyond the pressure corresponding to the actual load or beyond the vehicle manufacturer's recommendation.

Oversteer
The situation that occurs in cornering when the rear of a vehicle tends to skid before the front.

Plies
The reinforcing members of a tyre composed of layers of cord fabric and rubber that provide the strength to contain the air pressure needed to support a load and resist deflection.

Radial
The tyre construction utilizing plies that run radially from bead to bead under the tread. This construction requires a belt to stabilize the tread and define the tire diameter.

Revolutions per km
The measured number of revolutions made by a tyre traveling one km.

Rim
The portion of a wheel incorporating the well, seats, and flange onto which a tyre is mounted.

Rim Diameter
The diameter of the rim bead seats that support a tyre, normally indicated in whole numbers in inches for passenger cars.

Rim Width
The distance between rim flanges.

Rollover
The condition that occurs during hard cornering when a tyre sidewall rubs the road surface.

Rotation
The systematic movement of tyres from one vehicle position to another to maximize tread life and minimize irregular wear.

Run Out
The measure of the out of roundness of the tyre causing a vibration that cannot be balanced.

Section
A slice of a tyre from one bead, through the tread to the other bead.

Section Height
The vertical distance from the bead edge to center of the crown in an unloaded tyre.

Section Width
The distance between a tyre's sidewalls measured at the widest part of the tyre. Each size of tyre is measured on a specific rim width.

Series
A designation of a tyre's aspect ratio. A tyre with an aspect ratio of 60% is a 60 series tyre.

Shoulder
The edge of a tyre's tread where it joins the sidewall.

Sidewall
The portion of the tyre between the bead and the tread. It is flexible to soak up bumps yet stiff to limit tyre rollover.

Slip Angle
The angle between the direction in which a tyre is aimed or steered and the actual direction of tyre travel.

Speed Rating
A letter designation identifying the tyre's high-speed durability on an indoor test wheel. Refer to the speed-rating chart.

Toe
The difference between the front and rear edges of tyres mounted on an axle. Toe-in means the front edges are closer together than the rear edges and tyres point inward. Toe-out means the front edges are farther apart than the rear edges and the tyres point outward.

Tread
The region of a tyre designed to contact the ground. It is molded of tough rubber for high traction and low wear.

Tread Pattern
The arrangement of blocks, grooves, sipes, and channels designed into the tread to enhance its grip. Also called the tread design.

Tread Void
Areas in the tread, such as grooves and channels, that permit water to drain away from the footprint.

Treadwear
The measure of the life of a tyre tread.

Tubeless
A tyre construction that uses a rubber inner liner inside the casing to prevent air leakage and eliminate the need for an inner tube.

Underinflation
The condition that exists when there is not sufficient air pressure in a tyre to support a specific load. This causes the tyre to operate with excessive deflection and rollover.

Understeer
The condition that exists during cornering when the front of a vehicle tends to skid before the rear.

Wheel Alignment
Refer alignment.