ALIGNMENT
The checking and adjustment of caster camber and toe angles in a vehicle's suspension to maintain specifications engineered by the vehicle manufacturer for optimum performance.

ASPECT RATIO
The relationship between the section height and section width of a tyre expressed as a percentage of section width. If the section height is one half the section width, the aspect ratio is 50%.

BALANCE
The equal distribution of the mass of the tyre and wheel assembly for smooth driving. Balance is achieved by fitting weights to the wheel rim to offset uneven weight distribution of the tyre or wheel.

BEAD
An inextensible hoop of high tensile steel wires which anchors the plies and conforms to the rim seat to hold the tyre onto the wheel rim.

BEAD SEAT
The inner ledge portion of the wheel rim where the tyre bead rests adjacent to the flange.

BELTS
The band of multiple tyre cords compressed of usually rubberized steel wires beneath the tread and laid at opposing angles that determine the tyre's diameter and stabilizes the tread by resisting deformation from cornering, braking and centrifugal forces. These do not tie into the tyre beads.

BIAS-PLY
A type of tyre construction utilizing plies (usually rubberized fabric cords) that run diagonally from one bead to the other. One ply is set on a bias in one direction, and succeeding plies are set alternately in opposing directions crossing each other. Sometimes called a cross-ply tyre.

BLT
Raised Black Lettering

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 which 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.

CONTACT PATCH
The area of the tyre's tread that is in actual contact with the ground. (See Footprint.)

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.

DOT
Department of Transportation (DOT) code on tyre walls

DSST
Dunlop Self-Supporting Technology. An advanced tyre design that permits limited driving after loss of inflation pressure. Requires a pressure monitoring system.

EC
'E' number marked on sidewall

FOOTPRINT
The area of the tyre's tread that is in actual contact with the ground. (See Contact Patch)
Harmonic markings on wheels and tyres that allow match mounting to cancel tyre and wheel runout, minimizing vibration.

FUL
Full Load

HFS
High speed use at full load

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

HSN
High speed use at normal load

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 the air inside a tyre, which applies a tensile stress to the tyre cords, permitting them to carry the vehicle's load.

LINER OR INNER-LINER
The thin layer of halobutyl rubber inside a tyre that contains the inflation air, sometimes called the inner-liner. All Dunlop passenger tyres are manufactured with an inner-liner.

LR
Low Rolling Resistance

MIXING TYRES
Fitting tyres of different sizes, ratings or constructions to a vehicle. Mixing should be avoided. Some performance vehicles, however, specify different size tyres on front and rear axles. See vehicle's Owner's Manual.

MOUNTING TYRES
The act of fitting tyres to wheel rims.

NRM
Normal load

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 of 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 and rotate in the original direction of travel.

OWL
Outlined White Lettering

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 whose cords run radially from bead to bead under the tread. This construction requires a belt to stabilize the tread and define the tyre diameter.

REVOLUTIONS PER MILE
The measured number of revolutions made by a tyre traveling one mile.

RF
Reinforced

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 are normally indicated in whole numbers in inches for passenger cars.

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

RUNOUT
The measure of the out-of-roundness of the tyre causing a vibration which cannot be balanced.

RIM WIDTH
The distance between rim flanges.

RWL
Raised White Lettering

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.

SL
Slim Line White Lettering

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 ECE 30 European Indoor Wheel Test Standards.

TL
Tubeless Tyre

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, usually described in number of miles.

TT
Tubed Type Tyre

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.

UNDER INFLATION
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, mechanical flexing and heat.

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

WHEEL ALIGNMENT
See Alignment.