The amount of air inside the tire pressing outward on each square inch of tire, which is expressed in pounds per square inch (psi) or kiloPascals (kPa), the metric designation for air pressure.
Formulated with virtually impermeable butyl rubber, this material replaces the inner tube in modern, tubeless tires. Check you air pressure monthly, as some air loss occurs over time.
When all wheels on the vehicle are adjusted so that they are pointed in the optimum direction relative to the road and each other.
Tires that deliver a measure of traction on snow and ice without sacrificing dry performance driving capabilities.
Tires that provide a good balance of traction in rain or snow with good tread life and a comfortable, quiet ride.
Indicates the tire’s ability to provide a balance of traction in wet, dry, and winter conditions.
An advanced silica-based winter rubber compound that helps provide flexibility where the tread surface makes contact with the road.
An extremely dangerous situation where water builds up in front of the tires resulting in the tires losing contact with the road surface. At this point, the vehicle is skimming on the water surface and is completely out of control. Also called hydroplaning.
A synthetic fabric used in some tires that is (pound-for-pound) stronger than steel.
The relationship of a tire’s sidewall height to its section width.
Different tread patterns featured on either side of the tread that enhance and optimize performance for both wet and dry handling. The inside shoulder has more grooves for water evacuation and massive tread blocks on the outside shoulder make for maximum handling.
The state in which a tire and wheel spin with all their weight distributed equally. To correct an imbalance, a trained mechanic will add weights on the interior or exterior of the wheel.
The section of the tire that sits on the wheel. Inside, there is a round hoop of steel wires, wrapped or reinforced by body ply cords, that clamps the tire firmly against the wheel rim.
A key component of the tire that is the contact point between the tire and the wheel, designed to withstand forces the wheel puts on the tire during mounting as well as the dynamic forces of driving and braking.
Responsible for transferring propulsion and braking torque from the wheel rim to the road surface contact area.
Two sidewall plies wrapped around each bead wire in opposite directions providing lateral stability but flex to absorb road irregularities.
A rubber-coated layer of cords that is located between the body plies and the tread. Cords are most commonly made from steel but may also be made from fiberglass, rayon, nylon, polyester or other fabrics.
A type of tire with crossed layers of ply cord running diagonally to the center line of the tread.
The diameter of an imaginary circle drawn through the center of each lug nut hole and then measured from two holes that are directly across from each other. The measurement is used in selecting the proper wheel for replacement.
A technique practiced by drag racers and road testers to improve their off-the-line acceleration; applying the brake and throttle at the same time, increasing the engine rpm until release of the brake.
A term used to describe a loss of traction when negotiating a curve or when accelerating from a standing start. The tires slide against, instead of grip, the road surface.
Synthetic rubber used to create today’s tires. It is virtually impenetrable to water and air.
A wheel’s inward or outward tilt from vertical, measured in degrees. The camber angle is adjusted to keep the outside tires flat on the ground during a turn.
Side or lateral force generated when a tire rolls with camber, which can add to or subtract from the side force a tire generates.
This is a reinforcing filler which, when incorporated into the tire rubber compound, gives it a high resistance to wear.
The supporting structure of the tire consisting of plies anchored to the bead on one side and running in a radius to the other side and anchoring to the bead. Also called casing.
Made up of thin textile fiber cables bonded into the rubber. These cables are largely responsible for determining the strength of the tire.
At a given air pressure, how much weight each tire is designed to carry. For each tire size, there is a load inflation table to ensure the inflation pressure used is sufficient for the vehicle axle load.
The angle between a line drawn vertically through a wheel’s centerline and the axis around which the wheel is steered; improves a car’s directional stability and on-center feel.
An imaginary line down the center of the vehicle. Alignment tracking is measured from this line.
The sideways acceleration, measured in g’s, of an object in curvilinear motion. As a car traverses a curve, centrifugal force acts on it and tries to pull it outward. To counteract this, the tires develop an equal and opposite force acting against the road. Also called lateral force.
The amount of air pressure in a tire, measured in pounds per square inch (psi) before a tire has built up heat from driving.
An added rubber tire component between the tread and belt that absorbs road irregularities for a smoother ride.
The area in which the tire is in contact with the road surface. Also called footprint.
The strands of fabric forming the plies or layers of the tire. Cords may be made from polyester, rayon, nylon, fiberglass or steel.
The force on a turning vehicle’s tires - the tire’s ability to grip and resist side force - that keeps the vehicle on the desired arc.
A sipe pattern that provides lateral and longitudinal stiffness within the tread block.
Provide the rigid base for the tread which allows for good fuel economy. The plies also provide centrifugal and lateral rigidity to the tire, and are designed to flex sufficiently for a comfortable ride.
Weight of a production vehicle with fluid reservoirs (including fuel tank) full and all normal equipment in place, but without driver or passengers.
The tread and sidewall flexing where the tread comes into contact with the road.
The ability of a vehicle to be driven safely and with confidence in a straight line and at high speed without being affected by pavement irregularities, crosswinds, aerodynamic lifting forces, or other external influences.
Track is the width between the outside tread edges of tires on the same axle. Tracking, or more specifically
Dog Tracking, refers to a condition in which the vehicle is out of alignment, and the rear wheels do not follow in the path of the front wheels when the vehicle is traveling in a straight line. Also called tracking.
A code molded into the sidewall of a tire signifying that the tire complies U.S. Department of Transportation motor vehicle safety standards.
Drift refers to a vehicle deviating from a straight-line path when no steering input is given. Also called pull.
Tires placed side by side on an axle to increase both carrying capacity and traction capability; four tires across an axle.
Employs two compound types across the tread, the outside for dry traction and the inside for wet traction.
An instrument used to measure hardness. Specific to tires, a durometer typically measures the hardness of the tread compound. Durometer can also refer to the hardness result, as in
The tire’s durometer is 60.
Exists when the weight is equally distributed both around its circumference and on either side of its centerline. A tire and wheels assembly that is out of dynamic balance will produce a wobble effect or a shaking from side to side.
Mounting of a tire wheel assembly in such a way that the center of rotation for the assembly is not aligned with the center of rotation for the vehicle’s hub.
The Economic Commission of Europe develops motor vehicle requirements. ECE-approved tires must meet standards for physical dimensions, branding requirements and high-speed endurance regulations.
Tires that are rated to carry a higher load by virtue of having a maximum inflation pressure higher than the standard maximum.
Individual, spiral-wrapped nylon or aramid/nylon reinforcing filaments can be precisely placed in specific portions or across the entire tread area atop the steel belts banded at zero degrees. Not only does this help retain tire shape, but it also enhances ride quality and steering precision.
Transfer of weight from the front axle to the rear axle (or vice versa) caused by acceleration or braking. Acceleration causes weight transfer from the front axle to the rear axle. Braking causes weight transfer from the rear axle to the front axle.
A handling term describing a car with its front and rear tires sliding in a controlled manner. The driver uses both throttle and steering to keep the vehicle on a prescribed path.
The radius of the tire/wheel assembly that is not deflected under load.
The space between two adjacent tread ribs; also called tread grooves.
The maximum weight that can be distributed among the tires on a given axle.
The weight of the vehicle and its contents (fluids, passengers, and cargo).
The maximum weight allowed for the vehicle and its contents. This value is established by the vehicle manufacturer and can be identified on the vehicle door placard.
Tires with lower sidewalls and wider treads that yield better traction on surfaces such as sand and soft soil found in watery, off-road situations.
Also called maximum performance, ultra-high-performance, etc., offer a superior degree of handling, grip, and cornering ability than standard tires. High-performance tires are also rated for operation at higher speeds than non-high-performance tires.
Also called summer tires; designed for wet-and-dry weather driving, but not for use on snow and ice.
Wheels are manufactured to fit either the hub or the lugs. Hub-centric wheels match the hub hole of a custom wheel perfectly to the diameter of the hub of the vehicle.
When rubber stretches and compresses, it does not render all the energy applied to it because energy is lost due to internal friction. The mechanical energy is transformed into thermal energy and the heat produced leads to both damage and energy loss.
A normal, safe occurrence in a tire’s sidewall where overlapping splices of fabric cords form indentations. This cannot occur on tread due to steel cable implantation.
The act of putting air into tires.
The innermost layer of a tubeless tire, compounded with virtually impermeable butyl rubber. Some air loss over time will occur. Check your pressures monthly to ensure safe reliable operation of your tires.
S-shaped sipes that interlock, creating greater sipe length for extra tractive grip.
The metric unit for air pressure. One psi is equal to 6.9 kPa.
Side-to-side wobbling of a wheel as it rotates; a shimmy.
When a vehicle travels through a curve, weight is transferred from the wheels on the inside of the curve to the wheels on the outside of the curve. This is a result of the centrifugal force, or lateral force acting on the vehicle.
Automotive industry term for smaller trucks, pickups, passenger vans, or SUVs.
A term used to characterize steering response.
Indicates how much weight a tire is certified to carry at maximum inflation pressure.
The measurement in inches from the wheel axle centerline to the ground when the tire is properly inflated for the load.
The height of the section of the tire that is making contact with the road.
An assigned number ranging from 0 to 279 that corresponds to the load-carrying capacity of a tire.
Defines a range of maximum loads that tires can carry at a defined pressure.
Wheels are manufactured to fit either the hub or the lugs. Lug-centric is matching the lug holes of a custom wheel perfectly to the lug pattern of the vehicle.
Generally designed for luxury sedans, this breed of tires blends performance handling with a comfortable, smooth ride.
All-season rating designation for tires that can perform at certain levels in mud and snow conditions. Meets the Rubber Manufacturers Association (RMA) definition of a mud and snow tire.
Technique that matches the harmonic high point of a tire with a low point of the wheel to insure optimal ride performance.
The maximum air pressure to which a cold tire may be inflated; can be found molded onto the sidewall.
One system used to describe a tire’s size. It is the standard system of the ETRTO (European Tire and Rim Technical Organization).
The result of your vehicle’s front and/or rear suspension not being properly aligned.
This is the act of putting a tire on a wheel and ensuring that the assembly is balanced. When you purchase new tires, they need to be professionally mounted. It is also standard for the tire dealer to charge a nominal fee for a valve stem.
Alignment setting where the tops of the tires are leaning toward the centerline of the vehicle; racers use a negative camber angle for maximum cornering potential.
When the wheel mounting face is closer to the brake side of the wheel, moving the tire and wheel assembly out of the fender well.
National Highway Traffic Safety Administration.
The diameter of a tire rim, given in nearest whole numbers (e.g. 15 in.).
The offset of the rim is what locates the tire/wheel assembly in relation to the suspension. A wheel with zero offset has a mounting face that directly aligns to the wheel’s centerline.
To achieve the optimal weight balance between the tire and the wheel, the assembly can be taken off the vehicle and balanced to eliminate both side-to-side shimmy and hopping up and down.
Tires selected by a vehicle manufacturer that best match tire performance to vehicle performance characteristics. Also known as OE.
The diameter of the inflated tire, without any load.
The distance between the outside of the two sidewalls, including lettering and designs.
Too much air in the tire, resulting in premature wear in the center of the tread.
The tendency for a vehicle, when negotiating a corner, to turn more sharply than the driver intends. The rear end of the vehicle wants to swing toward the outside of a turn. A handling condition in which the slip angles of the rear tires are greater than the slip angles of the front tires. An oversteering car is sometimes said to be “loose,” because its tail tends to swing wide.
Rust process that takes place in the steel belts when moisture, via damage, is allowed to get inside the tire. This can result in the tire becoming unserviceable before normal replacement time.
A simple, commonly-used test to check the proper tread depth on a tire with an upside-down penny. To learn how to use the Penny Test, click here.
An option allowing drivers to customize their vehicles by mounting low-profile tires on wider rims (one or two inches greater in diameter), usually enhancing vehicle appearance, handling, and performance.
A rubber-coated layer of fabric containing cords that run parallel to each other and make up the structure of a tire. Layers of this material are called plies, and they extend from bead to bead, between the inner liner, and belts or tread. Plies are usually reinforced with either textile or steel cords.
Uniform designation of tire sizes, in metric measurements originally introduced by American tire manufacturers in 1977; commonly called P-metric series. A typical P-metric tire is P205/70R14 93S.
A tire designed to be filled with air.
Alignment angle that makes the top of the tires farther apart than at the bottom; tires are tilted out from the centerline of the vehicle.
Alignment setting when the steering axis is inclined rearward at the top.
The mounting face of a wheel is toward the wheel’s street side, moving the tire and wheel assembly in toward the vehicle.
Technology that creates a uniform compound blend that helps provide outstanding all-around performance in wet and dry conditions.
Abbreviation for pounds per square inch, which is the automotive industry’s measurement of the pressure in a tire.
A condition in which a vehicle swerves to one side without being steered in that direction, as a result of irregular tire wear, improper front and/or rear wheel alignment, or worn or improperly adjusted brakes.
A type of tire with plies arranged so cords in the body run at 90-degree angles to the center line of the tread.
A racing-derived compound optimized for on-track performance and designed for maximum dry grip and repeated heat cycles.
Also called rpm. Measured number of revolutions for a tire traveling one mile. This can vary with speed, load, and inflation pressure.
A pattern of tread features aligned around the circumference of a tire. There are usually multiple ribs across the tread area of a tire.
The distance from the ground to a fixed reference point (differs by automaker) on the vehicle’s body. This dimension can used to measure the amount of suspension travel or the height of the body from the ground.
That portion of a wheel to which a tire is mounted.
The diameter of the rim bead seats supporting the tire.
Also called drop center, a change (drop) in the rim profile between the rim flanges in which the bead area of a tire is placed during the mounting process. This allows the tire to be mounted on the rim.
Surface of the rim of the wheel that contacts the side of the tire bead.
The linear distance traveled by a tire in one revolution (its circumference). This can vary with load and inflation. Rolling circumference can be calculated as follows: 63,360 divided by revolutions per mile = rolling circumference in inches.
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 changing of tires from front to rear or from side to side on a vehicle according to a set pattern; provides even treadwear. Rotating your tires on a regular basis (every 6,000-8,000 miles) is a simple way to add miles to their life. See your tire warranty for more information on recommended rotation.
A combination of raw materials blended according to carefully developed procedures. The rubber compound is specially adapted to the performance required of each type of tire.
Tires that are designed to resist the effects of deflation when punctured, and to enable the vehicle to continue to be driven at reduced speeds and for limited distances.
The amount a wheel moves in and out, away from its true center as it is rotated. If runout is excessive, the wheel can be seen to wobble as it rotates.
The height of a tire, measured from its rim to its outer tread.
The distance between the outside of a tire’s sidewalls, not including any lettering or designs.
When the tire is cornering, torque created at the road contact patch acts at a point somewhat to the rear of the actual wheel center due to pneumatic trail. This has the same effect as positive caster and tends to force the wheel back to the straight-ahead position.
Tires with the same aspect ratio, or relationship of section height to section width.
Numbers and letters molded into the sidewall indicating the load-carrying capacity, load index, and the speed at which the tire can carry a load under specified conditions, or the speed rating. Also known as load index and speed symbol.
Wobbling of wheels from side-to-side on a vehicle. Shimmying can be caused by a variety of factors, including improperly balanced tires, poor alignment, and bent wheels.
The area of a tire where the tread and sidewall meet.
Also known as dynamic imbalance, this is when weight is not evenly distributed around a wheel’s circumference or its centerline. The result is a feel of the car shaking from side to side.
That portion of a tire between the tread and the bead. Protects the tire against impacts with curbs, etc. This is also where the sidewall markings can be found which tell you important information regarding the tire.
In 1992, Michelin discovered how to incorporate this new reinforcing filler into the rubber compound of tires. The discovery paved the way for compounds that provided resistance to wear, low rolling resistance, and good road-holding.
A compounding of silica with a specially formulated synthetic elastomer for exceptional grip on cold and wet surfaces, as well as reliable durability.
One tire mounted on each side of an axle (two tires per axle).
Special slits within a tread block that open as the tire rolls into the contact patch then close, breaking the water tension on the road surface and putting rubber in contact with the road to maintain adhesion, increasing wet and snow traction.
The combination of tire width, construction type, aspect ratio, and rim size used in differentiating tires.
The difference between the linear speed of the vehicle and the rotational speed of the tire. For example, if a tire is locked and sliding (e.g., not rotating) while the vehicle is still moving, then it is operating at -100% slip.
The difference between the direction the wheel is traveling and the direction the vehicle is traveling.
Also called winter tire; a special type of tire with a tread pattern and compound that gives better traction in snowy and icy conditions; identified by the M+S, M&S, or M/S on the sidewalls.
An alphabetical code (A-Z) assigned to a tire indicating the range of speeds at which the tire can carry a load under specified service conditions.
The parts of a car that are supported by its springs, including the frame, engine and body.
Flexing of the tread blocks between the belt package and the road surface. Less squirm means better steering response; more squirm means worse steering response.
Situation in which the driver maintains control of the vehicle.
A staggered fitment is putting larger wheels on the back of your vehicle than the front of your vehicle.
The amount of weight a given size tire can carry at a recommended air pressure.
A pattern for tightening the lug nuts when mounting the tire and wheel assembly to the vehicle. This pattern assures uniform pressure, prevents misalignment, and helps keep the wheel centered.
Exists when the weight mass is evenly distributed around the axis of rotation. Static imbalance can be detected from vibrations through the seat, floor and steering column.
Distance from the wheel axis of rotation to supporting surface at a given load and stated inflation pressure.
The combination of steel cords covered with rubber that forms a strip or belt placed under the tread rubber and on top of the casing (carcass); ensures uniformity when the tire is rotating and helps prevent flats.
A vehicle’s reaction to a driver’s steering inputs. Also the feedback that drivers get through the steering wheel as they make steering inputs.
The entire mechanism that allows the driver to guide and direct the vehicle; includes the steering wheel, steering column, steering gear, linkages, and wheel supports.
A design feature at the base of the groove that generates an additional gripping mechanism in deeper snow.
The way in which a tire carcass is constructed. Radial structure tires can be identified by the word radial or by the letter R and today account for the majority of vehicle tires.
Small bumps in the shoulder grooves help to provide lateral block rigidity.
The various springs, shock absorbers and linkages used to suspend a vehicle’s frame, body, engine, and drivetrain above its wheels.
Uniform tread pattern on both sides of the tread for better performance in specific conditions and on specific roads.
Man-made, as opposed to natural, rubber. Most of today’s passenger car and light truck tires have a relatively small amount of natural rubber in their content.
Tire and Rim Association.
An object’s resistance to stretching or breaking when placed in tension. Steel belts in a tire are characterized and compared based on their tensile strength.
Also called pneumatic tire, a precisely engineered assembly of rubber, chemicals, fabric, and metal, designed to provide traction, cushion road shock and carry a load under varying conditions.
An alphanumeric code molded into the sidewall of the tire that describes the tire’s size, including width, aspect ratio, rim diameter, load index, and speed rating. Most designations use the P-Metric system.
A situation in which tires of various brands, types, or sizes are mixed on a vehicle. This can lead to variations in the vehicle’s ride and handling characteristics.
A metal or paper tag permanently affixed to a vehicle, which indicates the appropriate tire size and inflation pressures for the vehicle. The placard can ordinarily be found on either the driver’s doorpost, the glove box lid, or the fuel-filler door.
Tool used to properly measure the air pressure in a tire.
The difference in distance between the front and rear of a pair of tires mounted on the same axle.
The fronts of two tires on the same axle are closer than the rears of the tires.
The fronts of two tires on the same axle are further apart than the rears of the tires.
Also known as Ackerman Angle. A vehicle’s wheels on the inside of a turn follow a smaller radius than the tires on the outside of the turn, because the two front wheels steer at different angles when turning.
Turning or twisting effort, usually measured in lb-ft or Newton meters.
Sipes with vertical undulation (into tread block) for added rigidity during cornering.
A long, straight bar fastened to the frame at one end and to a suspension part at the other; acts like an uncoiled spring that absorbs energy by twisting.
Generally offer increased tread life, comfort, and all-season traction.
The distance between the outside tread edges of two tires on the same axle.
The friction between the tires and the road surface; the amount of grip provided.
A state in which a vehicle bounces up and down abnormally.
That portion of a tire that comes into contact with the road. It is distinguished by the design of its ribs and grooves. Provides traction in a variety of conditions, withstands high forces, and resists wear, abrasion, and heat.
Scraping rubber off the tread. Also known as shaving.
The depth of usable tread rubber measured in 32nds of an inch. If a tire comes new with 10/32nds of rubber, you have 8/32nds of usable rubber. Tires must be replaced when the wear bars are visible at 2/32nds.
The life of a tire before it is pulled from service; mileage.
The tread section that runs around the circumference of the tire separated by the tread grooves.
Narrow bands, sometimes called wear bars, that appear across the tread of the tire when only 2/32 inch of tread remains.
The width of a tire’s tread.
A process that makes it possible to precisely place three different types of rubber compounds across the tread of a tire.
Specialized sidewall shape, bead area, and bead compound that enhance the durability and mountability of tires with very short sidewalls.
Operating a tire without sufficient air pressure to support the weight of the vehicle with occupants and additional load; could cause failure of the tire when heat is generated inside the tire to the point of degeneration of components.
The handling characteristic in which the front tires break loose because they are running a larger slip angle than the rear tires. Also known as plowing.
Material between the bottom of the tread rubber and the top layer of steel belts; acts as a cushion that enhances comfort.
Also known as directional tread, this is a tire designed to only rotate in one direction.
The weight of the parts of a vehicle not supported by its springs, including wheels and tires, outboard brake assemblies, the rear axle assembly, suspension members, springs, shock absorbers and anti-roll bars.
Also known as Uniform Tire Quality Grading Standards. A government-sponsored tire information system that provides consumers with ratings (from AA to C) for a tire’s traction and temperature. Treadwear is normally rated from 60 to 700.
A device that lets air in or out of a tire. It is fitted with a valve cap to keep out dirt and moisture, plus a valve core to prevent air from escaping.
A system that maximizes the contact patch area during cornering through a combination of asymmetrical tread patterns and underlying belts.
The process of varying the size of tread blocks around the circumference of a tire to minimize the noise generated by the tire as it rolls.
Two types of sipe technology that increase the rigidity of the tread under loaded conditions, such as cornering, braking, or accelerating. This technology allows tread block surfaces to
lock together (in both longitudinal and lateral directions), resulting in precise and responsive steering, short braking distances, and improved transmission of engine torque to the driving surface.
Vertical bouncing, or static imbalance, exists when the weight is not evenly distributed around the wheel’s axis of rotation. You can feel this through the floor, seat and steering column.
Can occur just after a rain shower wets down a dry road surface. Oil on the road surface migrates to the top of the layer of moisture, and can be very slippery, even when the layer of moisture is very thin. Continuing rain lessens the condition by washing the oil away.
The irreversible process of heating rubber under pressure to improve its strength and resilience.
A vehicle’s tendency to stray or wander from its intended direction of travel as a result of steering abnormalities, worn tires, suspension misalignment, crosswinds, or pavement irregularities.
Indicates how efficiently the tire disperses water to combat aquaplaning, and how well it grips wet roads in low-speed driving.
The longitudinal distance from the center of the front wheel to the center of the rear wheel on the same side of the vehicle.
Small weights attached or secured to the wheel to balance the tire and wheel assembly.
When the mounting face of the wheel directly aligns with the wheel’s centerline.
When tires on the same axle are parallel; the fronts and rears of the tires are equidistant.