Tire Glossary

[ A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | XYZ ]

A

Air Pressure: Force exerted by air within tire, expressed in psi or bar

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.

Anchored Beads: Beads, ply and flipper construction that locks beads in place in the tire. Rubber-coated cord fabric is wrapped around high tensile strength steel wire, which has been insulated with rubber. The ends of the fabric, which are several inches in length, are then carried far up into the sidewall of the carcass and locked in by the plies when the tire is vulcanized.

Aquaplaning: Rolling over a film of water, it is the phenomenon caused by a tire that is building up a water front (like a wave) slightly ahead of the tire itself. When speeding, this waterfront makes the car "surf" on a certain portion of the water front itself, with the effect of lifting the car slightly off the ground: this is what causes a rapid loss of contact with ground, a quite scary sensation, when felt on the steering wheel by the driver.

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

Asymmetric Tread Pattern: When opposite sides of a tire's tread pattern are not identical.

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 height, the aspect ratio is 50%.

B

Balance: 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.

Bead: That part of the tire that is shaped to fit the rim. Made of high tensile steel wires that are wrapped in woven fabric and then held by the plies.

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

Bead Wires: Metal cords holding a tire tightly to the wheel rim.

Belted Bias Tires: Have a body similar to that of bias tires, plus two or more belts under the tread to strengthen and stabilize the tread. The belts improve tread life by reducing tread movement during contact without the road.

Belts: The plies of tire cords beneath the tread that determine the tire's diameter and stabilize the tread by resisting deformation from cornering, braking, and centrifugal forces.

Bias-Ply: 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.

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

Buckling: A condition when a tire is bulging or crumpling.

C

Camber: 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.

Carbon Black: In the tread compound chemical mix, a reinforcing filler agent that when put into the rubber increases the wearing resistance of the latter.

Carcass: That portion of a tire that is the foundation for the tread, belts, bead and sidewall. The tire's load-bearing framework. (See Casing)

Casing: The tire body composed of plies which form the tire'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.

Chafer Reinforcing: fabric and rubber around the bead in the rim flange area to prevent chafing of the tire by rim parts.

Compound: The general term referring to the chemical formula for the tread material.

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 tire.
Contact Patch (or Contact Area): The surface over which a tire stays in contact with the ground.

Cord: The twisted fiber or filament of polyester, rayon, nylon or steel which gives the tire carcass and belts strength.

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

Crown: The center area of a tire's tread.

D

Deflection: The deference between a tire's unloaded or free radius and the loaded radius.

Diagonal (Bias) Tires: Have two, four or more body plies, which cross at an angle to the center line of the tread, to strengthen both the sidewall and the tread.

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

DOT Marking : Serial numbers on tires (DOT 4TLM YAN 1502) signifying that tire meets or exceeds Department of Transportation Safety Standards
4T Manufacturer and Plant Code Number (KUMHO Koksung Plant)
LM Tire Size Code Number (205/55R16)
YAN Group of Symbols Optional with the Manufacturer
1502 Date of manufacturing (Week 15, Year 2002)

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

Durability: This is one of the six functions of a tire. The tire must endure and outlast varying conditions. The best durability equates to the best possible level of performance and resistance to damage during millions of wheel rotations.

E

Extra Load (or XL): Passenger car tires designed for loads and inflation pressures higher than the standard versions.

F

Filler: 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.

Footprint: see Contact Patch.

G

Grip: Relationship between 2 materials (tire/ground) which can be reinforced by the texture of the surfaces.

Grooves: Circumferential channels between the tread ribs of a tire.

H

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

High Performance Tire: In the tire industry, those tires with speed ratings of H or greater and aspect ratios of 65 or less.

Hydroplaning: see Aquaplaning

Hysteretic: Actions and reactions: not all energy applied to a tire becomes totally absorbed by the latter. There is always an energy loss that transforms into "heat" when dealing with an elastic material like rubber.

I

Imbalance: 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. Pressures should always be checked when the tires are cold. Don't forget to check the spare tire to ensure that you conform to the manufacturers' recommendations. See Over Inflation and Under Inflation.

Inner Liner: The layer of halobutyl rubber which is laminated to the inside of a tubeless tire to insure the air retention quality of the tire body.

J

N/A

K

Kerfs: see Sipes

L

Light Truck Tires: Tires designed for off-the-road and on/ off-the-road use on sport/utility, small commercial, and recreational vehicles.

Liner: see Inner-liner.

Load index: The load index represents the maximum load in kilograms that can be supported by the 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.

Load Carrying Capacity: Maximum load for which tire is designed under standard conditions.

Load Range: A system of designations, which identifies the carrying capacity range of a tire. These markings shown on the tire indicate the ply rating established for the tire. Passenger tire designations are B (4-Ply rating), C (6-Ply Rating) and D (8-Ply rating). This system was established by the Rubber Manufacturers' Association and is used on all American-made tires. Replaces ply rating.

Low-Profile: A term describing a tire with a low relative aspect ratio or series classification.

M

Metric Tire Size System: A tire sizing system using the section width (mm), aspect ratio, speed category, tire construction, and the rim diameter (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.

Mounting Tires: The act of fitting tires to wheel rims.

M & S: (M+S) This is a marking found on Winter Tires and stands for Mud & Snow.

N

Nominal Section Width: The section width of an inflated tire mounted on its theoretical rim and indicated in the tire size designation.

O

Overall Diameter: The diameter of an 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 linear distance between the outsides of the sidewalls of an inflated tire including elevations due to labeling (marking), decorations, or protective bands or ribs.

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.

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

P

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

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.

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

Polyester Cord: A synthetic fiber that excels in maintaining strength properties at high heat levels, and eliminates flat spotting.

Pressure Gauge: Instrument used to measure tire pressure.

Q

N/A

R

Radial: The tire 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. Also called a Radial Ply.

Radial Tires: Body cords run across the tire perpendicularly to the beads. Radial tires have belt plies, which run circumferentially around the tire under the tread to stabilize the tread and strengthen the tread area. By restricting tread movement during contact with the road, the belt plies improve tread life.

Rayon: An artificial fiber made from cotton or wood pulp by chemical process.

Reinforced Tires (or RF): Car tires especially designed to withstand heavier loads and higher pressure levels than the standard tire.

Reliability: The tire must provide safety and reliability at varying speeds, throughout its life.

Revolutions Per Mile (R.P.M.): The number of revolutions that the mounted tired will make in one mile, at rated load and inflation.

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

Rim: 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: The distance between rim flanges.

Rolling Resistance: The resistance of a tire to free rolling. The lower the rolling resistance, the more economic it is to roll the tire as less energy will be required to "roll the tire" with a resulting fuel saving and higher mileage.

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

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

Runout: The measure of the tire's circumference distortion causing a vibration that cannot be balanced.

S

Section: 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 unloaded tire.

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

Series: See Aspect Ratio

Service Description: In addition to the tire Size Designation a tire may be identified by a Service Description consisting of a load index (or two Load Indices in the case of single/dual fitments) and a speed symbol.

Shoulder: The area of a tire where the tread and sidewall meet.

Sidewall: That portion of a tire between the tread and the bead. It is flexible to soak up bumps yet stiff to limit tire rollover.

Silica: A reinforcement filler used with the rubber compound to provide higher wearing resistance and low rolling resistance.

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

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 tread wear.

Steer Wheel(s): The wheel(s) that direct the course of a vehicle.

Stud Holes: Small cavities along a tire's tread designed to hold tire studs for increased traction on snow-covered surfaces.

Stud Holes Speed Category: Indicates tire speed capabilities above 240 km/h and are included within the tire size designation e.g. 215/50 ZR 15. Generally, Service Description is not shown on such tires. For actual speed capabilities and load capacities, consult the tire manufacturer concerned.

Speed Symbol: Indicates the max speed at which the tire can carry a load corresponding to its load index (except for speeds above 210 km/h) under service conditions specified by the tire manufacturer.

Stability: Ability of tires to maintain direction of vehicle on curve without causing excessive sway.

Summer Tire: Tire designed specifically for optimal driving on dry, warm, cold and wet surfaces, but not on snow or ice.

Symmetrical Tread Pattern: Tread pattern which is consistent across the tire. Both halves of the tread are the same design.

T

Tire Compound: A "mix" or combination of raw materials used in the manufacture of the rubber compound of the tire itself. By varying the percentage or the composition of the materials applied, manufacturers can produce different tires for various purposes and with different performances.

Tire Profile: A term representing the portion of a tire measured as its aspect ratio or series.

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

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

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

Tire Structure: Implies the method used to manufacture the tire carcass. The two main methods are "Radial" and "X-Ply".

Toe: 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.

Tread: The area where the tread and sidewall meet. The region of a tire designed to contact the ground. It is molded of tough rubber for high traction and low wear.

Tread Depth: The distance in thirty seconds of an inch measured from the tread surface to the bottom of the grooves in a tire.

Tread Pattern (Design): Design of the tread area. Tread pattern varies according to the tire purpose (i.e. rain/wet are more grooves and channels for optimum water dispersion, whilst dry/tarmac tires are less grooved as they function is to maximize the contact area with the ground). The arrangement of blocks, grooves, sipes, and channels designed into the tread to enhance its grip.

Tread Elements: The parts of the tread design, which are separated from each other and made distinct by the sipes and rib or lug designs, molded into the tire.

Tread Life: Length of service in miles before tread wears out.

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

Tread Wear Indicators: Narrow bars of rubber molded at a height of 1.6mm (2/32inch) across the bottom of the tread grooves. When the tread wears down to these bars, the tire should be replaced. Legal minimum tread depth states that the grooves of the tread pattern of every tire fitted to the wheels of a vehicle shall be of a depth of at least 1.6mm throughout a continuous band comprising the central three-quarters of the breadth of tread and round the entire outer circumference of the tire.

Tubeless: A tire inflated without a separate inner tube. A tire construction which uses a rubber inner liner inside the casing to prevent air leakage and eliminate the need for an inner-tube.

Tube-Tire: Tire with a separate inner tube.

U

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.

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

UTQG (Uniform Tire Quality Grade): UTQGS is a standard defined by the DOT of USA for grading the performances of tires in the areas of TREADWEAR, TRACTION and TEMPERATURE RESISTANCE. It applies only to car tires with a rim diameter of 13" and larger, but not to winter tires.

Tread Wear: The measure of the life of a tire tread. The tread wear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear one and one-half times as well on the government course as a tire graded 100. The relative performance of tires depends upon the actual conditions of their use, however, and may depart significantly from the norm due to variations in driving habits, service practices and differences in road characteristics and climate.

Traction: The traction grades, from highest to lowest, are AA, A, B, and C. Those grades represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete. A tire marked C may have poor traction performance. Warning: the traction grade assigned to this tire is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning, or peak traction characteristics.

Temperature: The temperature grades are A (the highest), B, and C, representing the tire's resistance to the generation of heat and its ability to dissipate heat when tested under controlled conditions on a specified indoor laboratory test wheel. Sustained high temperature can cause the material of the tire to degenerate and reduce tire life, and excessive temperature can lead to sudden tire failure. The grade C corresponds to a level of performance which all passenger car tires must meet under the Federal Motor Safety Standard No. 109. Grades B and A represent higher levels of performance on the laboratory test wheel than the minimum required by law. Warning: the temperature grade for this tire is established for a tire that is properly inflated and not overloaded. Excessive speed, under inflation, or excessive loading, either separately or in combination can cause heat buildup and possible tire failure.

V

Valve: The device used to let air in or out of a tire.

Varied-Pitch Ratio: Variations in angles and sizes of a tire's tread elements that reduce ride noise levels.

W

Weather Cracking: Fine hairline cracks in surface of rubber, caused by oxidation and other atmospheric effects.

Wheel Diameter: The diameter of the wheel in inches.

Winter Tire: Tire designed principally for driving in wet, cold, snowy and icy surfaces. Identifiable by the M+S (Mud & Snow) marking on the tire sidewall.

XYZ

N/A