TIRE TERMINOLOGY
A
ADJUSTMENT - A prescribed allowance given to a customer toward the replacement of product pursuant to the warranty.
AGING - Deterioration of physical and chemical properties of rubber by oxidation over a period of time.
AIR PRESSURE - Force exerted by air within a tire, expressed in pounds per square inch or kilopascals (kPa).
ALIGNMENT - Angles of the tire and suspension axis relative to each other and the ground: camber, caster, toe. Also, the adjustment of components to bring them into a predetermined position for the most efficient operation of wheel and vehicle for proper even tire wear.
ANTIOXIDANT - A chemical, which when added to a rubber compound, prevents surface oxidation; used in tire tread and sidewall compounds to prevent weather checking and cracking.
ASPECT RATIO - The dimensional relationship between tire section height and section width; section height divided by section width.
B
BALANCE - A uniform mass distribution of a tire and wheel assembly about its axis of rotation.
BEAD - The area of the mounted tire which seats against the wheel
BEAD FILLER - A rubber extrusion in the bead area of a tire; used to permit a smooth contour of casing plies around the bead and to the lower sidewall. Also used in enlarged form to stiffen the lower sidewall of a tire.
BEAD SEAT - The position where the tire rests and seals on the inside of the rim.
BELT - An assembly of fabrics and/or wire under the tire's tread used as a reinforcement. It also constrains the outside diameter against inflation pressure and centrifugal force.
BELT EDGE WEDGE OR INSERT - An extrusion of rubber placed under the edges of a belt; used in radial tires to improve durability.
BLOCK - An individual part (or "element") of tire's tread.
BODY - The fabric inner structure of the tire.
BREAKAWAY - The point at which tire cornering traction is lost.
C
CONICITY - Quality or state of being conical. (Cause of radial tire pull.)
CONTACT PATCH – The part of the tire in contact with the road surface. See Footprint.
CORD - Fabric or steel wire strands forming plies and belts in tires.
CORD ANGLE - The degree at which the plies or belts cross the centerline of any given tire.
CORNERING FORCE - The force that turns a vehicle around a corner. The opposite of lateral or centrifugal force.
CROSS-SECTION WIDTH - External sidewall- to-sidewall measurement of inflated tire, exclusive of ornamental ribs and lettering. Sometimes called section width.
CROWN - The region between the shoulders of the tire.
CURB GUARD - A rubber protrusion running circumferentially around some tires just above the rim flange to reduce curb scuffing of the wheel.
CURB WEIGHT - The total weight of a vehicle with no passengers and a full tank of gas.
C.U.V. - Crossover Utility Vehicle.
D
DEFLECTION – The difference between a tire’s unloaded or free radius and the loaded radius.
DESIGN RIM - A rim with a specified width; used to determine basic tire dimensions.
D.O.T. - A tire branding symbol, signifying the tire meets requirements of the Department of Transportation.
DRIVE WHEEL APPLICATION - Describes tires, which are designed specifically for optimum performance on drive wheels.
DUAL COMPOUND TREAD - A tire tread with two rubber compounds.
DUALS - On light trucks, this describes two tire and wheel assemblies mounted on each side of a drive axle.
DYNAMIC BALANCE – A condition in which a tire and wheel assembly has weight distributed equally on both sides of the wheel’s axis of rotation. Also referred to as “spin balancing” or “computer balancing”.
E
ETRTO - European Tyre and Rim Technical Organization.
EURO METRIC TIRE SIZE SYSTEM - A tire sizing system originating in Europe stating the cross section (in millimeters), aspect ratio, tire construction type, rim diameter (in inches), load index and speed symbol (e.g.: 185/70R14 88T).
EXTRA LOAD - A P-Metric tire with a maximum inflation of 41 psi. or 50 psi. For Euro-Metric tires, the term ‘reinforced’ means the same as “Extra Load”. Extra Load tires’ added reinforcement combined with higher permitted air pressures enable them to carry greater loads than Standard- or Light-Load tires.
F
FABRIC - Material made up of parallel cords used in tire construction.
FLOTATION TIRE - A light truck tire designed to offer enhanced traction and impact absorption in off-road driving.
FOOTPRINT - The area of a tire’s tread where it meets the road surface. See Contact patch.
G
GROOVES - Circumferential channels between the tread ribs of a tire.
GROSS AXLE WEIGHT RATING (GAWR) - The maximum weight that the front or rear axle can carry. The front and rear gross axle weights must not exceed the front and rear GAWR’s.
GROSS COMBINATION WEIGHT RATING (GCWR) - The total weight of the loaded tow vehicle and the loaded trailer.
GROSS VEHICLE WEIGHT (GVW) - The total weight of the vehicle, including passengers, fuel, cargo, and attachments.
GROSS VEHICLE WEIGHT RATING (GVWR) - The maximum permissible loaded weight of the vehicle and takes into account the capabilities of the engine, transmission, frame, spring, brakes, axles, and tires. The GVW must not exceed the GV
H
HIGH FLOTATION SIZING SYSTEM FOR LIGHT TRUCKS - A system displaying overall diameter in inches, section width in inches, type of tire construction, and rim diameter in inches (e.g.: 33x12.50R15LT). See Flotation Tire.
I
IMBALANCE - A non-uniform distribution of mass in a tire and wheel assembly about its axis of rotation causing bounce (static imbalance) or shake (dynamic imbalance).
INNERLINER - A layer of low-permeability rubber laminated to the inside of a tubeless tire to make it hold air.
K
KILOPASCALS (kPa) - Unit of air pressure; in metric terms it takes 6.895 kPa to equal 1 p.s.i.
L
LIFT POINTS - Specific contact points on a vehicle chassis to be used when lifting it for service. To prevent serious injury to persons and/or permanent vehicle damage, owners’ manuals should always be consulted for proper lift point locations prior to lifting or jacking a vehicle. Also known as “jacking points”.
LOAD CARRYING CAPACITY - The load a particular size tire can carry at a given inflation pressure under certain driving conditions, as established by the Tire and Rim Association.
LOAD INDEX - A numerical code associated with the maximum load a tire can carry at the speed indicated by its Speed Symbol under specified service conditions up to 130 mph. For speeds in excess of 130 mph, actual load on the tire shall be reduced in accordance with Tire and Rim Association guidelines.
LOAD RANGE - Replaces the former ply rating term and identifies load and inflation limits.
LOAD RATING - The weight that a wheel is designed to support in normal service.
LT-METRIC - A light truck sizing system expressing the section width in millimeters, aspect ratio, type of construction, and rim diameter in inches (e.g.: LT235/85R16 120/116Q E).
M
M + S, M/S, or M & S—A tire sidewall designation indicating that the tire meets the USTMA/RAC definition of an all-season tire.
MATCH MOUNTING - A mounting procedure that matches the high point of a tire with the low point of its wheel to help ensure a smooth ride. A dot or mark on the tire is matched with a dot, a sticker, or the valve hole on the wheel.
MOUNTAIN SNOWFLAKE PICTOGRAPH – Winter passenger and light truck tire design identification. Tires with this symbol provide improved snow performance compared to tires meeting the USTMA/RAC all-season tire definition.
N
NHTSA - National Highway Traffic Safety Administration.
NOMINAL – A designated or theoretical size that may vary from the actual.
O
ORIGINAL EQUIPMENT (OE) - Refers to tires sold to automobile manufacturers for installation on new vehicles.
OUT-OF-ROUND - A wheel or tire condition in which the wheel or tire is not round.
OVERALL DIAMETER - The diameter of an unloaded of a tire when mounted on a wheel and inflated to rated pressure.
OVERINFLATION - The inflation of a tire above the car manufacturer’s recommended pressure. May result in a rough ride, bruise damage, and premature wear of suspension components.
OVERSTEER - A cornering condition where rear tires lose traction before the front tires; the tendency of a car to turn more sharply than the driver intends while negotiating a turn.
OXIDATION - Reaction of a material with oxygen, usually resulting in degradation of the material.
P
PERMEATION – The process where air molecules migrate through the sidewalls of the tire. Tires lose air normally through the process of permeation.
PITCH - The length from a point on one tread block to the same point on the next tread block. Pitch is varied around a tire to minimize noise.
PLIES - The layers of material that make up the cord body and belts of a tire.
PLOWING - Loss of traction of front tires during cornering. also known as understeer or “pushing ”.
PLUS 1/PLUS 2 CONCEPT - A concept to improve handling and performance through the mounting of tires with wider section widths and lower section heights to rims of 1, 2 and sometimes even 3 inches greater diameter. Correct Plus 1 or Plus 2 fitments maintain the same tire diameter as the original tires.
P-METRIC SYSTEM - A tire sizing system expressing the section width in millimeters, aspect ratio, type of tire construction, rim diameter in inches, load index and speed symbol (e.g.: P225/70R15 100S).
POLYESTER - A strong and lightweight synthetic cord material used in casing construction.
POLYMER - A chemical compound made up of a large number of identical components linked together like a chain.
PSI - Pounds per Square Inch.
PULL - The tendency of a vehicle to drift to one side when driving straight.
R
RADIAL RUNOUT - A measurement of out-of-roundness; by rotating the inflated tire and measuring how far the tread surface varies (up and down) from a true circle.
RADIAL TIRE - A tire built with casing plies arranged at a 90 degree angle to the center line of the tread.
RAYON - A synthetic cord material used in casing and belt construction; provides high dynamic strength and good rubber adhesion.
REVOLUTIONS PER MILE (RPM) - The number of revolutions a tire makes in a mile.
RIBS - The rubber elements at the tire tread which contact the ground, oriented in a generally circumferential direction.
RIM DIAMETER - The diameter of the bead seat of the wheel, (and not it’s edge or “flange”).
RIM FLANGE - The outermost edge of a wheel’s rim to which clip-on weights are attached.
RIM WIDTH - The measurement inside of the rim flanges; i.e. from inside the flange on one side to inside the flange on the other side.
ROLLING RESISTANCE - The force required to roll a loaded tire.
ROTATION - The pattern of movement of tires to different positions on a vehicle to compensate for irregular or unequal tire wear.
RUBBER-TO-VOID-RATIO - The ratio between the rubber area and the groove area in a tire footprint.
RUNOUT GAUGE - A device used to check radial and lateral runout.
S
SAFETY HUMP - The raised area circling the rim of the wheel and located slightly inward from the bead seat. It's purpose is to keep the tire from slipping into the rim well, if accidentally deflated while driving.
SECTION HEIGHT - The distance from the bottom of the bead to the top of the tread.
SECTION WIDTH - The distance from sidewall to sidewall, exclusive of any raised lettering.
SERIES - The ratio of the height of a tire (from the bead seat to the top of the tread) to the width of the tire (from sidewall to sidewall). It is also referred to as the aspect ratio or “profile” of a tire.
SERVICE DESCRIPTION (LOAD INDEX/SPEED SYMBOL) – The Service Description consists of a Load Index and a Speed Symbol. The Load Index is a numerical code that specifies the maximum load a tire can carry at the speed indicated by its Speed Symbol, at maximum inflation pressure.
SHIMMY - A rapid oscillation or wobble of a wheel and tire assembly about the steering axis.
SHOULDER –The outer edges of a tire’s tread where it joins the sidewall.
SIDEWALL - The side of a tire between the tread shoulder and the rim bead.
SIDEWALL ROLLOVER –The condition that occurs during hard cornering when a tire sidewall contacts the road surface.
SIPES - Small, narrow slots molded into the tread elements which increase the number of traction edges of the tire and improve its traction on wet, snowy or icy pavement.
SLIP ANGLE - The difference between the direction a tire is traveling and the direction it is pointing.
SLOTS - Grooves positioned in the ribs and shoulders of the tread to aid wet pavement traction.
SPEED RATING (SPEED SYMBOL) – An alphabetical system describing a tire’s maximum permissible speed under specified laboratory conditions. It also serves as an indication of the tire’s performance (emergency response and stability, braking traction, etc.) at everyday speeds.
SQUIRM - Distortion of tread elements in the footprint of a tire as it rolls.
STABILITY - The ability of tires to maintain direction of a vehicle on curves without causing excessive body sway.
STANDARD LOAD - A P-Metric tire with a maximum inflation pressure of 35, 44, or 51 psi.
STAR PATTERN - The proper method for sequential tightening of lug nuts in a 5-lug bolt circle.
STATIC LOADED RADIUS - The measurement from the middle of the axle to the road surface; measured with the tire inflated to required pressure and carrying the rated load.
STEEL BELT - A belt material used in tires. Its high stiffness provides good handling and low tread wear.
STEERING RESPONSE - Reaction time between driver input at the steering wheel and the directional change of the vehicle.
SYNTHETIC RUBBER - Rubber made from chemicals as a substitute for natural rubber; properties can be tailored for specific needs.
T
TENSILE STRENGTH - The maximum tensile force per cross-section area that a material can withstand before it breaks.
TORQUE - The product of a force applied through a lever arm to produce a rotating or turning motion.
TORQUING - The securing of the tire/wheel assembly to the vehicle by the tightening of the wheel’s lug nuts to the studs of the vehicle’s hub; in the case of specialty wheels, torquing should always be done with a manual torque wrench.
TPMS - TIRE PRESSURE MONITORING SYSTEM - DEVICE MANDATED BY THE NHTSA (USA) TO HELP MOTORISTS MAINTAIN PROPER TIRE AIR PRESSURE.
TREAD - The portion of a tire which contacts the road surface.
TREAD DEPTH - The distance from the tread surface to the bottom of the grooves
TREAD RADIUS - The radius of curvature of the tread arc across the tread.
TREAD SHAVING - The buffing of tread from a tire with a blade (usually to half of original tread depth) to reduce tread squirm and tearing in racing applications.
TREAD WEAR INDICATORS - A raised ridge positioned laterally across the tread grooves which becomes even with the tread surface when the tire is worn to 2/32” tread depth; used to define the legal wear-out point in a tire’s life.
U
UNDERINFLATION - A condition where a tire is inflated below the carmaker’s recommended pressure.
UNDERSTEER - A cornering situation where the front tires generate more slip angle than the rear tires; the tendency of a car to turn less sharply than the driver intends and compensated for by the addition of more steering input.
UNDULATION - A slight indentation or wavy appearance on the sidewall surface of an inflated radial tire. Radial body ply cords run straight across the tire from bead to bead and the joining of the ply material in the sidewall area may sometimes cause this condition. Undulation is a common characteristic of radial tires and will not affect the performance of the tire. Refer to the USTMA “Tire Information Service Bulletin”, Volume 21 / Number 1, dated December 1984, for more information.
UNIFORMITY - A term describing the amount of radial and lateral force variation in a tire.
USTMA - United States Tire Manufacturers Association
UTQG - Uniform Tire Quality Grade labeling; a performance measurement of a tire, based upon its test results in three categories: treadwear, traction, and temperature resistance.
V
VULCANIZATION - The linking together, under heat and pressure, of rubber compound polymers, which gives rubber increased strength and elasticity.
W
WHEEL WEIGHT - Weights that are either clipped, taped, or self-adhered to the inside or outside of the wheel in order to balance the tire/ wheel assembly.