Tire glossary

Tire Terms Defined

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Air Pressure

The pressure of air inside the tire expressed in pounds per square inch (psi) or kilopascals (kPa).


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.

All-Season Tires

Tires designed for use on dry or wet pavement which also provide traction on snow and ice.

All Terrain

Tires with larger tread blocks designed to be used both on highways and off-highway driving


See hydroplaning


A synthetic fiber that is, per weight, stronger than steel. Used in tire construction and provides excellent high tensile strength to weight.

Aspect ratio

The relationship between the section height and section width of a tire expressed as a percentage of section width. If the section height is one half the section width, the aspect ratio is 50%. Low aspect ratio tires are also known as low profile tires.


Describes a tire's tread pattern which has one side different from the other.

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


The part of a tire which is in contact with the rim comprised of a round hoop of steel wires, wrapped or reinforced by ply cords.

Bead seat

The inner ledge portion of the wheel rim where the tire bead rests adjacent to the flange.


The plies of tire cords beneath the tread that determines the tire's diameter and stabilizes the tread by resisting deformation from cornering, braking, and centrifugal forces.


A type of tire construction utilizing plies 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 tire.

Block Design

A tire tread pattern made of raised rubber- compound segments.


The individual, raised rubber-compound segments making up the tread of a tire.


A condition when a tire is bulging or crumpling.

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

Camber thrust

A cornering force generated by the tire's camber.


That portion of a tire that is the foundation for the tread, belts, bead and sidewall. See casing.


The tire body, composed of plies which form the tire's structure and give it shape. Sometimes called the carcass.


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


A finishing strip of calendered fabric used to protect the tire's bead area from the rim.

Cold Inflation Pressure

The amount of pressure in a tire, measured before a tire has built up heat from driving.


The general term referring to the chemical formula for the tire's material.


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 tire.


The strands of material forming the plies or layers of the tire. Cords may be made from steel, fibreglass, rayon, nylon, polyester or other materials.

Contact patch

(See Footprint)

Cornering force

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


The center area of a tire's tread.

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

Directional stability

The tendency for a tire to roll in it's steered direction rather than follow road contours.

Drive Wheel(s)

The wheel(s) that provide the power or driving force for a vehicle.

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The material used to fill the area above the bead between the outer and inner portion of the sidewall. Also used in enlarged form to stiffen the lower sidewall of a tire.


The area of the tire's tread that is in actual contact with the ground. (also: Contact Patch)


The resistance to slippage between the tires and the road surface.

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Channels between the tread ribs of a tire, also called Tread Grooves.

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H-Speed or H-Performance Rated

A speed category for tires with a maximum speed capability of 130 MPH.

Harmonic marking

Markings on wheels and tires that allow match mounting to cancel tire and wheel runout, minimizing vibration.

Heat cycling

A process of preparing competition tires for use through  controlled heating and rolling pressure.

High Performance Tire

1) Tires with speed ratings of S or greater and aspect ratios of 70 or less. 2) Yokohama uses the term for tires with an aspect ratio of 70 or less and a speed rating of H, V or Z.

Highway Tires

Also called Summer tires; designed for wet- and dry-weather driving, but not for use on snow and ice.

Hoop strength

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


The accumulation of water in a film under the footprint which causes a tire to lift from the road surface, losing traction. Hydroplaning is affected by vehicle speed, tread pattern, and water depth. Also known as aquaplaning

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The condition that exists when a tire'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 tire which applies a tensile stress to the tire cords permitting them to carry the vehicle's load. Usually expressed in Pounds per square Inch (psi)


The interior layer of a tubeless tire. The innerliner prevents air from permeating through the tire.

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Kilopascal (kPa)

The metric unit for air pressure. There are 6.9 kPa to 1 psi.

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Light Truck Tires

Tires designed for off-the-road and on/off-the-road use on sport/utility, small commercial and recreational vehicles. Sometime called Sport Truck tires.


The thin layer of rubber inside a radial tire that contains the inflation air, sometimes called the inner-liner. Virtually all modern passenger tires are manufactured with an inner-liner.

Load Index

An assigned number ranging from 0 to 279 that corresponds to the load carrying capacity of a tire.

Load Rating

A method of rating a tire's load-carrying capacity (denoted by letters such as B, C, D, etc.) with respect to its ply rating.


A term describing a tire with a low relative aspect ratio or series classification.

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Mud and Snow.  Used to designate a tire with special design characteristics to improve performance in mud and snow.

Maximum Inflation Pressure

The maximum air pressure at which a cold tire is designed to be operated, moulded onto the sidewall. It should not be confused with the vehicle manufacturer's recommended operating pressure, which is frequently lower.

Metric Tire Size System

A tire sizing system using the section width expressed in millimeters (mm), aspect ratio, speed category, tire construction and the rim diameter in inches. Example: 185/70SR13.

Mixing tires

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


The act of installing tires on wheel rims.

Mud Terrain Tires

Tires with large tread blocks designed specifically for use in mud, sand, rocks and other off road driving conditions

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Overall diameter

The diameter of a mounted, unloaded, inflated tire 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.

Overall Width

The distance between the extreme outer sides of a tire's two sidewalls, including lettering and designs.

Over inflation

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


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

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P-metric System

A tire sizing system using the section width in millimeters (mm), aspect ratio, type of tire construction and rim diameter in inches. Example: P225/70R15.

Passenger Car Tire

Automobile tires featuring aspect ratios of 70 or greater, using a taller profile for increased ride comfort.

Performance tire

Tires which are designed to provide higher than average traction at a speed rating of H or higher.  The enhanced traction may result in a shorter tread life due to the softer rubber compound used.

Plies (singular Ply)

The reinforcing members of a tire 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.


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 Rating

The designation of a tire's strength base on the equivalent number of cotton cord plies.  For example a tire with an 8 ply rating may have only 2 plies, but have the same strength as 8 cotton plies.

PSI or Pounds per square inch

The imperial unit for air pressure.

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The tire construction utilizing plies that cross the crown at an angle of 90 degrees and run radially from bead to bead under the tread. This construction requires a belt to stabilize the tread and define the tire diameter.


Parts of a tire tread pattern created by grooves that run circumferentially around the tire.

Revolutions per mile

The number of revolutions made by a tire traveling one mile.


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

Rim diameter

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

Rim Width

Distance between the two opposite inside edges of the rim flanges.

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.


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


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


The measure of the out of roundness of the tire causing a vibration which cannot be balanced.

Rim width

The distance between rim flanges.

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S-speed or S-performance rated

A speed category for tires with a maximum speed capability of 112 miles per hour.


A slice of a tire 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 inflated, unloaded tire.

Section width

The distance between a tire's sidewalls measured at the widest part of the tire, not including lettering or designs. Each size of tire is measured on a specific rim width.


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


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

Shoulder Blocks

Raised rubber-compound segments on the part of the tire tread nearest the sidewall.


The portion of the tire between the bead and the tread. This is the part of the tire visible when in is installed on a vehicle and viewed looking at the side of the vehicle.


Slits in the tire tread which appear to be small cuts in the surface of the tread that improve traction and help in keeping the tire cool.


The combination of tire width, aspect ratio, construction type and rim size used in differentiating tires. Examples: 175/70R13 or, 195/60R15


To slip or slide on the road when tires lose their rolling grip.

Slip angle

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

Snow Tire

Often referred to as a Winter tire, a special type of tire with a tread and compound that gives better traction in snow and other extreme winter conditions.

Speed rating

A letter designation identifying the tire's high speed durability on an indoor test wheel. Refers to European Commission for Europe
Regulation 30 (ECE 30) European Indoor Wheel Test Standards.

Sport Truck

See Light Truck

Steel Belt

A layer in the construction of radial tires under the tread. Its high stiffness provides good handling and low treadwear.

Steer Wheel(s)

Those wheel(s) which are used to steer or direct the course of a vehicle.

Stud Holes

Small cavities along a tire's tread designed to hold tire studs.  See Studded Tire.

Studded Tire

A special class of winter tire which incorporated steel studs that protrude from the tread for increased traction on snow and ice covered surfaces.

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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 conditions.

Tire Information Placard

A metal or paper tag permanently affixed to a vehicle that indicates the appropriate tire size and inflation pressure for the vehicle, as well as rim size and load capacity information. Commonly located on the door edge or door frame of the driver's side or on the inside of the glove compartment door.


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

Touring Performance Tire

A tire providing the ride comfort of a passenger car tire, yet possessing high performance tire characteristics.


The friction between the tires and the road surface, or the amount of grip provided.

Trailer Wheel(s)

The wheel(s) of a trailer unit that neither provide power nor direct the course of a vehicle.


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

Tread Blocks

Raised rubber-compound segments on the outside visible part of a tire.

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.

Tread Width

The width of a tire's tread.


A rating number moulded into the sidewall of the tire ranging from 60 to 620 determined by tire manufacturers which compares tire life against a predetermined standard tire (100).

Treadwear Indicator

Narrow bands, sometimes called wear bars, located in the tire grooves which are level with the tread surface when the tread thickness is only 2/32 inch, or less.


A variety of tire construction which uses a rubber inner liner inside the casing to prevent air leakage and eliminate the need for an inner-tube.

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Under inflation

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


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


Uniform Tire Quality Grade. A US government Department of Transport requirement for all tires sold in the USA. It is a tire rating system based on a tire's performance in treadwear durability, traction and temperature resistance. UTQG ratings must be marked on a tire's sidewall.

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V-Speed or V-Performance Rated

A speed category for tires with a maximum speed capability of 149 miles per hour.

Varied-Pitch Ratio

Variations in angles and sizes of a tire's tread blocks to reduce noise produced by the tire when in use.

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Wear Bars

See Treadwear Indicator.

Wheel alignment

See Alignment.

Winter Tires

Tires specifically designed for use in winter driving condition which may include rain, snow, and outside termperatures below freezing.

Z-Speed or Z-Performance Rated

A speed category for tires with a maximum speed capability of over 149 miles per hour.

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Also, you might find some other useful material in our consumer information page

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