Next Tires Wheel & Tire Terminology

Thank you for shopping with Next Tires, where we’re proud to offer a simple, Tire shopping experience. The following list of tire related terms and definitions will make understanding tire terminology a breeze, so you feel more confident when shopping for tires.

For a simple, tire glossary experience, use the letter index to go straight to each alpha-section of the Wheel and tire dictionary; select the Return to A – Z link to return to the Index. And for (more) answers to our most commonly asked questions, please visit our Frequently Asked Tire Questions page.

Next Tires Index of Tire Terms: A – Z

A B  C  D  E   F  G   H  I  K  L  M  N  O  P  R  S  T  U  V  W  Z

A

Accelerator – A chemical used in tire compounds, which speeds the vulcanization or hardening of rubber, to reduce curing time.

Activator – A chemical rubber compound used to help start the vulcanization or hardening process.

Adjustment – A credit manufacturer‘s give to customers, towards the replacement of a tire according to the product warranty.

Aging – The deterioration of the chemical and physical properties of rubber over time, primarily the result of oxidation.

Air Pressure – The force inside a tire made by air or nitrogen, most often referred to as kPa (kiloPascals) or PSI (pounds per square inch).

Alignment – The angles of the tires, wheels, steering and suspension, in relation to each other while driving on the road.

When your vehicle is in alignment, according to the automakers specifications, the wheels and tires are in the best position for:

• The most (fuel) efficient operation of your car, truck, crossover or sport utility vehicle; and,
• Even tire wear, which extends the life of your tires.

Impacts, like driving over a curb or hitting a pothole, can cause misalignment.

All-Season Tires – Tires that are engineered to provide good performance all year round. The Rubber Manufacturer’s Association, or RMA, defines the specifications for all-season tires, which have the M+S, M/S, or M&S mark on the sidewall, making them suitable for use in mud and (light) snow.

All-Terrain Tires – Tires that are engineered for traction on all kinds of surfaces, from highways to byways. All-terrain tires are designed to provide good, on-road handling, with an open, block tread made for off-roading.

All-Weather Tires – Tires that use a special rubber compound that stays flexible at temperatures above and below 7˚C or 44.6˚F, making them suitable for use as winter tires.

This increases grip and stability in all four-seasons and on a variety of roads and surfaces, from bare asphalt to fresh snow. All-Season tires use a rubber compound that gets cold and hard at temperatures below 7˚C or 44.6˚F, making them less effective tires during winter.

All-Wheel Drive or AWD – A transmission that always operates in four-wheel drive. AWD vehicles do not alternate with two-wheel drive.

Alphanumeric Rating – A load-based tire sizing system that includes a tire’s section width, aspect ratio, rim diameter, speed rating, load capacity, ply rating, and type of tire construction.

For example, take the following size for the Toyo Open Country C/T all-terrain truck tire – LT275/70R18 125/122Q E/10.

• Section Width – 275 (mm)
• Aspect Ratio – 70 (%)
• Rim Diameter – 18 (inches)
• Load Capacity – 125/122 (3,638/3,307 lbs)
• Speed Rating – Q (99 mph)
• Ply Rating – E/10 (80 psi/10 ply)
• Tire Construction – LT for Light Truck or P for Passenger and R for Radial

Anatomy of a Tire – The anatomy of a tire includes the tread, grooves, plies, belts, shoulder, sidewall and bead construction.

Anti-Roll Bar – A rigid, steel bar, connecting the left and right sides of a vehicle’s suspension, that improves handling, especially when cornering. As the car leans into a turn, the anti-roll bar stabilizes the car to prevent leaning by transferring more weight to the outside tires.

Antioxidant – A chemical that’s added to rubber compounds to prevent surface oxidation and weathering in tire treads and sidewalls.

Aspect Ratio – This is the relationship between the tire’s height or sidewall, and tread width. For example, in the popular tire size 205/55R16, the aspect ratio or height of the tire is equal to 55% of the tires width (205 mm).

Asymmetric or Asymmetrical – A tire engineered with different patterns on the inner and outer tire treads. An asymmetric tread design is most commonly used on high performance and ultra-high performance tires.

Autocross – An automotive competition, where cars race around an obstacle course, usually marked by cones.

Axle – A vehicle cross-support, on which its road wheels turn.

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B

Backspacing – This is the measurement from the back of the bolt pad to the back edge of the rim. It’s used to calculate wheel offset and determine where the back of the bolt pad is located in relation to the rim width and is sometimes referred to as rear spacing.

Balance – This is the uniform weight distribution of a tire and wheel around its center of rotation.

Balancing – Adjusting tires and wheels so they distribute weight and spin evenly around its center of rotation. Certified tire professionals and mechanics install balance weights on the wheel to correct wheel imbalances and tire wobble.

Bale Rubber – The form in which solid rubber is shipped to tire manufacturers.

Ball Joint – The ball-and-socket connection that allows a steering knuckle to move in several directions at the same time.

Bead – A round hoop of reinforced, steel wire on the inside of the tire, where it connects to, and sits in, the wheel’s bed seat. The bead is best kept in place by proper tire inflation.

Bead Filler – The smooth, rubber compound that extends up into and reinforces the tire sidewall.

Bead Seat – The small groove where the bead sits on the inside of the wheel and seals the tire to the rim. This seal works best with proper tire inflation.

Belt – A layer of natural and synthetic cords wrapped in rubber, located between the tire tread and the body plies. Cords are usually made of steel, but other materials include fiberglass, nylon, polyester and rayon.

In radial tires, the belt protects the tire’s outer diameter against (over) 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.

Bladder – A rubber bag filled with hot water or steam used to give shape to a tire during the molding and curing process.

Block – The part of a tire’s tread pattern created by lateral or side-to-side grooves.

Body – The supporting structure of the tire made up of plies that are anchored to the beads. This does not include the tread or sidewall rubber. Also called the carcass. 

Bolt Circle – Also called the wheel bolt pattern, is the diameter of an imaginary circle drawn through the center of each lug hole.

Braking Torque – Torque applied by a brake to a wheel and tire assembly, which slows or stops the vehicle.

Breakaway – This happens when a tire’s traction or grip is lost while cornering.

Bump Steer – A steering effect resulting from toe or camber changes as the suspension moves up and down.

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C

CUV – Crossover Utility Vehicle.

Carcass – The supporting structure, or body, of the tire made up of plies that are anchored to the beads. This does not include the tread or sidewall rubber. Also called the tire body. 

Conicity – Quality or state of a tire being cone-shaped. (Cause of radial tire pull.)

Contact Patch – The part of the tire that comes into contact with the road. Also known as the footprint.

Control Arm – A device used to connect the unsprung position of a suspension to the sprung chassis, which allows suspension travel.

Cord – Fabric layers that form plies and belts in tires. Cords are usually made of steel, but other materials include fiberglass, nylon, polyester and rayon.

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 Pattern – The sequential torquing of the wheel’s lug nuts in a pattern across from one another.

Cross-Section Width – Also called section width, this is the external measurement of an inflated tire, from sidewall-to-sidewall. This does not include ornamental ribs and lettering.

Crown – The area between the shoulders of the tire.

Crowned Road – A road design with a center slope or pitch, to the curb or shoulder, for better water drainage.

Curb Guard – A rubber guard running around some tires just above the whitewall to prevent curb scuffing on the tire sidewall.

Curb Weight – The total weight of a vehicle with a full tank of gas and zero passengers.

Cure – To vulcanize or harden rubber.

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D

D.O.T. Number – The 10 – 12 character code branded on the sidewall of tires sold in the United States, stating the tire meets the minimum requirements of the US Department of Transportation.

The code number includes information like tire size, type, manufacturer, manufacturing location, and date of manufacture (week and year).

Deflection – The difference between a tire’s unloaded or free radius and the loaded radius.

Directional Stability – The ability of a car, truck, CUV or SUV, to travel in a straight line with minimal driver control.

Directional Tread – Tires with directional tread are designed to roll in one direction. As a result, directional tires are used on one side of the vehicle and are rotated from front to back.

Dog Tracking – A driving condition where the rear wheels do not follow the path of the front wheels.

Double A-Arm – A suspension system which uses two “A”-shaped links or arms of unequal length to attach the upright supporting the wheels to the frame.

Drag Radial Tires – Also called racing slicks, drag radials are a type of tire with a smooth tread most commonly used in high performance, racing competitions.

Dual-Compound Tread – A tire tread with two rubber compounds.

Duals – Two tire and wheel assemblies, mounted on one side of an axle.

Durometer – The hardness measurement of a tire’s rubber compound and its resistance to penetration from a blunt, spring-loaded needle.

Dynamic Balance -The equal distribution of weight, or balance, of a wheel and tire while it’s rotating around the center axis. Also called Balance in Motion.

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E

Euro Metric Tire System – A tire sizing system expressing the cross section in millimeters, aspect ratio, tire construction, rim diameter in inches, load index and speed symbol, together also known as the service description (e.g. 185/70R14 88T).

Extra Load or XL – A P-Metric tire with a maximum inflation of 41 or 50 psi. This is sometimes referred to as ‘reinforced’. This higher pressure than a “Light Load” or “Standard Load” tire, allows for greater load capacity. This is great for off-road durability and towing capacity.

Extrusion – The process of forcing a material through an opening, to obtain a length of material used to create tire components.

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F

Fabric – A group of parallel cords used in the construction of the tire body or carcass. 

Flat Spot – Irregular wear in an isolated area of a tire’s tread.

Flotation Tire – A tire designed to minimize soil penetration and compaction. In other words, a tire designed to “float” across the surface of loose dirt, gravel, sand, and other soft surfaces.

For example, using tire size 35x12.50R18, sizing of flotation tires uses overall diameter in inches (35), section width in inches (12.50), type of tire construction (R), and rim diameter in inches (18).

Flush Fit – This occurs when the mounting pad of the rim or wheel goes into place freely and without obstruction against the hub-mounting surface.

Footprint – The mark left by a loaded tire’s tread as it meets the road surface. See Contact patch.

For and Aft Weight Transfer – This is the load factor when weight is transferred from the front to the rear tires during acceleration and from the rear to the front tires while braking.

Four-Season Tires – See All-Weather tires.

Four-Wheel Drive – This is a transmission system that delivers power directly to all four wheels of a vehicle. 4WD is most commonly found on trucks with off-road capabilities. 

Front-Wheel Drive – This is an engine and transmission design used in motor vehicles, to deliver power to the front wheels only.

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G

“g” – A symbol for, and unit of, acceleration that represents the force of gravity. The acceleration of one “g” equals 32 feet per second.

Green Tire – A tire that has not been cured, hardened or vulcanized.

Grooves – Channels that circle the tire between the tread ribs. Grooves provide room for debris to be flushed from beneath the tire for constant contact to the road or surface. 

Gross Axle Weight Rating (GAWR) – The maximum weight 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 its loaded trailer.

Gross Vehicle Weight (GVW) – The total weight of the vehicle, with passengers, cargo, fuel and any attached accessories.

Gross Vehicle Weight Rating (GVWR) – The maximum allowable, loaded weight of the vehicle, taking into account the capabilities of the engine, transmission, frame, spring, brakes, axles, and tires. The GVW must not exceed the GVWR.

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H

High Performance Tires – A type of summer tire optimized for improved grip and handling in dry and wet conditions, though not specifically designed for all-season traction.

As seen in the featured tire, the Hankook Ventus V2 concept2 all-season performance tire, the solid-continuous, center rib provides constant contact with the surface of the road. This provides more responsive steering and improved handling during more spirited, high performance driving.

High Pressure Die Cast – A wheel manufacturing process using aluminum alloys in special high-pressure die casting machines.

Highway Tires – An all-season tire, designed to handle the heavier loads of trucks and SUV’s. With such durable construction, highway tires better resist irregular tread wear and provide longer-lasting tread life (warranties).

Hub Centric – This occurs when the center bore hole of a wheel is made to match up with the hub diameter of the vehicle instead of the lug nuts.

Hydroplaning – A wet weather condition that occurs when steering stops responding because the tires aren’t making contact with the road; instead they’re riding on a layer of water.

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I

Idler Arm – A device attached to the frame  of the car, which duplicates the movement of the Pitman arm and keeps the center link aligned.

Imbalance – An uneven distribution of mass in a wheel and tire assembly, around its axis while rotating. This may cause bounce (static imbalance) or shake (dynamic imbalance) while driving.

Independent Suspension – A suspension system where the front or rear pair of wheels of a car or truck are independently connected to the frame or underbody. This setup helps limit deflection from one wheel being felt by the other wheel.

Inertia – The tendency of any mass at rest to stay motionless, or any mass in motion to remain moving.

Inner Liner – The layers of low permeability rubber, which are laminated to the inside of a tubeless tire to insure the air retention quality  of the tire body.

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K

kiloPascals (kPa) – Unit of air pressure where, in metric terms, 6.895 kPa equal 1 psi.

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L

Lateral Runout – The wobble or side-to-side motion of a rotating wheel and tire assembly.

Lateral Weight Transfer – A load factor in cornering, where weight is transferred from the inside to the outside tires.

Lift Points – The contact points on the chassis of a vehicle used to hoist the vehicle for servicing.

Light Load – A P-Metric tire with a maximum inflation pressure of 35, 44, or 51 psi (pounds per square inch).

Linerality – The ability of a vehicle to respond linearly to the driver’s steering input at low cornering levels.

Load Carrying Capacity – The maximum amount of weight a tire can carry, at a certain tire inflation pressure (psi or kPa), under ideal conditions. 

Load Index – An assigned number code, from 0 to 279, associated with the maximum load: (i) a tire can carry; (ii) at the speed indicated by its Speed Symbol (i.e. H); and, (iii) under specified service conditions up to 130 mph.

For speeds in excess of 130 mph, the actual load on the tire should be reduced in accordance with Tire and Rim Association guidelines.

Load Range – Once called ply rating, this is the combination (E/10) of load range (E) and ply rating (10), based on the number of plies (or layers) used in the construction of the tire body, indicating the tires load carrying capacity and strength.

Load Rating – The weight that a wheel is designed to support under normal conditions.

Load-Carrying Ball Joint – A ball joint that supports the weight of a vehicle.

Loading – The amount of weight put on tires. An increased load may increase cornering force.

Low-Profile Tire – A tire with a short sidewall (a lower aspect ratio). High performance tires, a type of low-profile tire, offer improved handling, but the ride can be rougher since there’s less tire cushioning between the wheel and the road.

LT-Metric – Using the size LT235/80R17 120/117R E/10 as an example, this Light Truck tire sizing system, expresses the section width in millimeters (235), aspect ratio (80%), type of construction (LT and R), rim diameter in inches (17), and the service description, or load (120/117), speed (R) and ply ratings (E/10).

Lug Centric – The centering of a wheel by matching it up with the attachment points (i.e. studs), rather than by the center bore hole of the wheel.

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M

M+S, M/S, or M&S – Symbols for Mud and Snow, on the sidewall indicating the tire meets the RMA’s definition of an all-season tire that are suitable for use in mud and (light) snow. True winter tires must also include the Three Peak Mountain Snowflake Symbol.

MacPherson Strut – A front suspension assembly that combines the functions of the shock absorber, the upper steering pivot, and the wheel spindle in a single unit.

Match Mounting – A mounting procedure that matches the high point of a tire with the low point of its wheel. A dot or mark on the tire is matched with a dot, a sticker, or the valve hole on the wheel.

Mounting Pad – The surface area of the back of the wheel’s center that contacts the brake drum or hub flange of the vehicle.

Mounting – The act of installing a tire on a wheel. Next Tires recommends new tires be mounted, balanced and installed by certified tire professionals.

Mud-Terrain Tires – Tires designed to be driven off-road, on a variety of uneven and loose surfaces, including gravel, mud, rocks, sand and soil. The large tread blocks and deep voids confidently, grab hold of the various surfaces and quickly clear debris, making sure mud-terrain tires have maximum traction.

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N

Negative Camber – A condition where the top of the tire is leaning inward from the tire’s vertical centerline, as viewed from the top. Often used on race cars for improved grip while cornering.

Negative Caster – A setting where the steering axis is inclined forward at the top as viewed from the side; a condition which tends to cause instability.

Negative Offsett – When the wheel mounting surface is toward the back, or brake side of the wheel. In a wheel with negative offset, the tire and wheel are moved out of the wheel well.

NHTSA – National Highway Traffic Safety Administration.

Numeric System – A tire sizing system expressing tire cross-section width (12.50, 13.50) and rim diameter (16, 18, 20) in inches.

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O

Off-Road Tires – Tires that use deeper tread blocks and wider grooves to provide more grip on all loose, soft, uneven or unpaved roads and terrain including dirt, gravel, mud, rocks, sand and soil.

Offset – The distance from the wheel mounting surface to the centerline of the wheel.

Original Equipment (OE) – Refers to the parts, in this case tires, chosen by automobile manufacturers for their new vehicles.

Out-of-Round – A condition in which the wheel or tire isn’t round.

Overall Diameter – The maximum height of a tire when mounted on a wheel and inflated to the recommended air pressure.

Overinflation – The inflation of a tire above the automaker’s recommended air pressure.

Oversteer – A cornering condition where the rear tires lose traction before the front tires.

Oxidation – The reaction of a material with oxygen, usually resulting in the breakdown of the material.

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P

P-Metric System – A passenger car tire sizing system using the section width in millimeters (225), aspect ratio (70%), type of tire construction (P and R), rim diameter (15) in inches, load index (100) and speed rating (S), combining as the tire size P225/70R15 100S.

Passenger Car – Vehicles with at least four wheels and (usually) no more than eight seats in addition to the driver’s seat, designed to transport passengers.

Penny Test – A simple test to check a tire for proper tread depth, using a penny.

Permeation – The process where air molecules slowly, escape through the sidewalls of the tire. Tires normally lose air 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.

Pitman Arm – A device in a recirculating ball steering system that converts circular motion into a back-and-forth motion through its connection to the system’s center link or relay rod.

Plasticizer – A chemical compound used to keep or make rubber soft and flexible.

Plowing – This happens when the front tires lose traction while cornering. It’s also known as understeer or pushing.

Plus 1 or Plus 2 Concept – The idea that handling and performance improve by mounting tires with wider section widths and lower section heights, or aspect ratio, to rims that are 1, 2 or 3 inches larger in diameter. Correct Plus 1 or Plus 2 fitments have the same tire diameter as the original tires.

Plus Sizing – Improving the appearance and performance of a vehicle by installing larger wheels and lower profile tires.

Ply or Plies – The rubber-coated layer(s) of fabric containing natural and synthetic cords that make up the body and internal structure of a tire. Plies run from bead to bead, in between the inner liner and the tire tread.

Ply Rating – Now called load range, this is the combination (E/10) of load range (E) and ply rating (10), based on the number of plies (or layers) used in the construction of the tire body, indicating the tires load carrying capacity and strength. See load range for graphic.

Polyester – A strong and lightweight synthetic cord material used in tire construction.

Polymer – A chemical compound made up of a large number of identical components linked together like a chain.

Positive Camber – An alignment condition where the top of a tire is leaning outward from the tire’s vertical centerline, as viewed from the top.

Positive Caster – A setting where the steering axis is leaning towards the rear at the top, as viewed from the side; makes possible the self-centering force that tends to return the wheel to the direction the vehicle is traveling.

Positive Offset – When the wheel mounting surface is toward the front, or street side of the wheel. On a wheel with positive offset, the wheel and tire are moved in toward the vehicle, resulting in narrower tracking.

PSI – Pounds per Square Inch.

Pull – The tendency of a vehicle to veer to one side when driving straight ahead.

Pyramid Belt – A belt design in which the upper layer is narrower than the lower layer.

Pyrometer – A thermoelectric device that measures a tire’s tread temperatures.

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R

Rack And Pinion System – A steering system that uses a round gear (or pinion) at the end of the steering column and connects with a rack of steel teeth, connected to the steering arms, that guide the wheels based on input from the steering wheel.

Radial Play – The lateral or side-to-side movement of a ball joint.

Radial Runout – This is a measure of a tires out-of-roundness and occurs when a tire’s radius is inconsistent from the midpoint of the rim to any point elsewhere on the wheel. 

Radial runout can be checked 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 that are arranged at an angle of 90 degrees to the tires direction of travel. 

Rayon – A corded, synthetic material, used in a tires belt and casing construction, that provides increased tire strength and excellent traction.

Rear Spacing – See Backspacing.

Rear-Wheel Drive – A transmission system in motor vehicles where the engine only powers the rear wheels. 

Returnability – The ability of a vehicle to return to a straight-ahead position after the removal of steering input.

Revolutions Per Mile (RPM) – The number of revolutions a tire makes in a mile at a given load, inflation, and speed.

Revolutions Per Minute (RPM) – The number of revolutions a machine makes in the given time frame. In vehicles, this is the number of times a crankshaft makes one full rotation per minute. 

Ribs – The rubber elements of the tire tread that contact the ground and are generally positioned in a circumferential direction.

Ride Height – The distance between the frame of the vehicle and the road.

Rim Diameter – The diameter of the bead seat, not the diameter of the rim edge.

Rim Drop – The area of the wheel’s rim having the smallest diameter.

Rim Flange – The outermost, flared edges of a wheel that prevent the tire from slipping off of the rim.

Rim Width – The measurement inside of the rim flanges, from one side of the flange to the other side.

RMA – The Rubber Manufacturer’s Association defines the specifications for all-season tires, which have the M+S, M/S, or M&S mark on the sidewall, making them suitable for use in mud and (light) snow.

Rolling Resistance – The force needed to keep a tire rolling at a uniform speed. The lower the rolling resistance, the less energy is required.

Rotation – Moving tires from front to rear, side to side, or in another set pattern in order to promote even tread wear and longer life.

Run-Flat – Tires built with self-supporting sidewalls that allow you keep driving after a puncture – at reduced speed and for a limited distance.

Runout Gauge – A tool used to check radial and lateral runout.

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S

Safety Hump – The raised area just inside the bead seat that circles the rim of the wheel, which keeps tires from slipping into the rim well when deflated.

Section Height – The distance from the bottom of the bead to the top of the tread.