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The amount of air inside the tyre pressing outward on each square inch of tyre, 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 tyres. 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.
Tyres that deliver a measure of traction on snow and ice without sacrificing dry performance driving capabilities.
Tyres that provide a good balance of traction in rain or snow with good tread life and a comfortable, quiet ride.
Indicates the tyre'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 tyres resulting in the tyres 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 hydro-planing.
A synthetic fabric used in some tyres that is (pound-for-pound) stronger than steel.
The relationship of a tyre’s sidewall height to its section width.
Different tread patterns featured on either side of the tread that enhance and optimise 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.Back to top
The state in which a tyre 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 tyre that sits on the wheel. Inside, there is a round hoop of steel wires, wrapped or reinforced by body ply cords, that clamps the tyre firmly against the wheel rim.
Responsible for transferring propulsion and braking torque from the wheel rim to the road surface contact area.
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 fibre-glass, rayon, nylon, polyester or other fabrics.
A type of tyre with crossed layers of ply cord running diagonally to the centre line of the tread.
The diameter of an imaginary circle drawn through the centre 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 term used to describe a loss of traction when negotiating a curve or when accelerating from a standing start. The tyres slide against, instead of grip, the road surface.
Synthetic rubber used to create today’s tyres. It is virtually impenetrable to water and air.Back to top
A manufacturing process that permits the precise placement of different tyre components and multiple rubber tread compounds.
A wheel’s inward or outward tilt from vertical, measured in degrees. The camber angle is adjusted to keep the outside tyres flat on the ground during a turn.
The side or lateral force generated when a tyre rolls with camber, which can add to or subtract from the side force that a tyre generates.
This is a reinforcing filler which, when incorporated into the tyre rubber compound, gives it a high resistance to wear.
The supporting structure of the tyre 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 fibre cables bonded into the rubber. These cables are largely responsible for determining the strength of the tyre.
At a given air pressure, how much weight each tyre is designed to carry. For each tyre size, there is a load inflation table to ensure that the inflation pressure used is sufficient for the vehicle axle load.
The angle between a line drawn vertically through a wheel’s centre line and the axis around which the wheel is steered; improves a car’s directional stability and on-centre feel.
An imaginary line down the centre of the vehicle. Alignment tracking is measured from this line.
The sideways acceleration, measured in Gs, of an object in curvilinear motion. As a car traverses a curve, centrifugal force acts on it and tries to pull it outwards. To counteract this, the tyres develop an equal and opposite force acting against the road. Also called lateral force.
The amount of air pressure in a tyre, measured in pounds per square inch (psi) before a tyre has built up heat from driving.
The area in which the tyre is in contact with the road surface. Also called footprint.
The strands of fabric forming the plies or layers of the tyre. Cords may be made from polyester, rayon, nylon, fibre-glass or steel.
The force on a turning vehicle’s tyres - the tyre’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.
These provide the rigid base for the tread which allows for good fuel economy. The plies also provide centrifugal and lateral rigidity to the tyre, and are designed to flex sufficiently for a comfortable ride.Back to top
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 road irregularities, crosswinds, aerodynamic lifting forces or other external influences.
The track is the width between the outside tread edges of tyres 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 travelling in a straight line. Also called tracking.
A code moulded into the sidewall of a tyre signifying that the tyre complies with 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.
Tyres placed side by side on an axle to increase both carrying capacity and traction capability; four tyres across an axle.
Employs two compound types across the tread, the outside for dry traction and the inside for wet traction.
Exists when the weight is equally distributed both around its circumference and on either side of its centre line. A tyre and wheels assembly that is out of dynamic balance will produce a wobble effect or a shaking from side to side.Back to top
Mounting of a tyre wheel assembly in such a way that the centre of rotation for the assembly is not aligned with the centre of rotation for the vehicle’s hub.
The Economic Commission of Europe develops motor vehicle requirements. ECE-approved tyres must meet standards for physical dimensions, branding requirements and high-speed endurance regulations.
Tyres that are rated to carry a higher load by virtue of having a maximum inflation pressure higher than the standard maximum.Back to top
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 tyres sliding in a controlled manner. The driver uses both throttle and steering to keep the vehicle on a prescribed path.
The radius of the tyre/wheel assembly that is not deflected under load.Back to top
The space between two adjacent tread ribs; also called tread grooves.
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.Back to top
Tyres with lower sidewalls and wider treads that yield better traction on surfaces such as sand and soft soil found in watery, off-road situations.
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.Back to top
A normal, safe occurrence in a tyre’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 tyres.
The innermost layer of a tubeless tyre, compounded with virtually impermeable butyl rubber. Some air loss over time will occur. Check your pressures monthly to ensure safe reliable operation of your tyres.
S-shaped sipes that interlock, creating greater sipe length for extra tractive grip.Back to top
The metric unit for air pressure. One psi is equal to 6.9 kPa.Back to top
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 vans, pick-ups, passenger vans or estate cars/4x4s.
A term used to characterise steering response.
Indicates how much weight a tyre is certified to carry at maximum inflation pressure.
The measurement in inches from the wheel axle centre line to the ground when the tyre is properly inflated for the load.
The height of the section of the tyre that is making contact with the road.
An assigned number ranging from 0 to 279 that corresponds to the load-carrying capacity of a tyre.
Defines a range of maximum loads that tyres 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.Back to top
All-season rating designation for tyres that can perform at certain levels in mud and snow conditions. Meets the Rubber Manufacturers Association (RMA) definition of a mud and snow tyre.
Technique that matches the harmonic high point of a tyre with a low point of the wheel to ensure optimal ride performance.
The maximum air pressure to which a cold tyre may be inflated; can be found moulded onto the sidewall.
One system used to describe a tyre’s size. It is the standard system of the ETRTO(European Tyre and Rim Technical Organisation).
The result of your vehicle’s front and/or rear suspension not being properly aligned.
This is the act of putting a tyre on a wheel and ensuring that the assembly is balanced. When you purchase new tyres, they need to be professionally mounted. It is also standard for the tyre dealer to charge a nominal fee for a valve stem.Back to top
Alignment setting where the tops of the tyres are leaning towards the centre line 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 tyre and wheel assembly out of the fender well.
The diameter of a tyre rim, given in nearest whole numbers (e.g. 38 cm/15 in.).Back to top
The offset of the rim is what locates the tyre/wheel assembly in relation to the suspension. A wheel with zero offset has a mounting face that directly aligns to the wheel’s centre line.
To achieve the optimal weight balance between the tyre 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.
Tyres selected by a vehicle manufacturer that best match tyre performance to vehicle performance characteristics. Also known as OE.
The diameter of the inflated tyre, without any load.
The distance between the outside of the two sidewalls, including lettering and designs.
Too much air in the tyre, resulting in premature wear in the centre of the tread.Back to top
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 towards the outside of a turn. A handling condition in which the slip angles of the rear tyres are greater than the slip angles of the front tyres. An over-steering car is sometimes said to be “loose”, because its tail tends to swing wide.
The rust process that takes place in the steel belts when moisture, via damage, is allowed to get inside the tyre. This can result in the tyre becoming unserviceable before normal replacement time.Back to top
A rubber-coated layer of fabric containing cords that run parallel to each other and make up the structure of a tyre. 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 tyre sizes, in metric measurements originally introduced by American tyre manufacturers in 1977; commonly called the P-metric series. A typical P-metric tyre is P205/70R14 93S.
A tyre designed to be filled with air.
Alignment angle that makes the top of the tyres further apart than at the bottom; tyres are tilted out from the centre line of the vehicle.
Alignment setting when the steering axis is inclined rearwards at the top.
The mounting face of a wheel is toward the wheel’s street side, moving the tyre and wheel assembly in towards the vehicle.
Abbreviation for pounds per square inch, which is the car industry’s measurement of the pressure in a tyre.
A condition in which a vehicle swerves to one side without being steered in that direction, as a result of irregular tyre wear, improper front and/or rear wheel alignment, or worn or improperly adjusted brakes.Back to top
A type of tyre with plies arranged so that the cords in the body run at 90-degree angles to the centre line of the tread.
Also called rpm. The measured number of revolutions for a tyre travelling one mile. This can vary with speed, load and inflation pressure.
A pattern of tread features aligned around the circumference of a tyre. There are usually multiple ribs across the tread area of a tyre.
The distance from the ground to a fixed reference point (differs by car-maker) on the vehicle’s body. This dimension can be 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 tyre is mounted.
The diameter of the rim bead seats supporting the tyre.
Also called drop centre, a change (drop) in the rim profile between the rim flanges in which the bead area of a tyre is placed during the mounting process. This allows the tyre to be mounted on the rim.
Surface of the rim of the wheel that contacts the side of the tyre bead.
The linear distance travelled by a tyre 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 tyre moving at a uniform speed. The lower the rolling resistance, the less energy needed to keep a tyre moving.
The changing of tyres from front to rear or from side to side on a vehicle according to a set pattern; provides even tread-wear. Rotating your tyres on a regular basis (every 6,000-8,000 miles) is a simple way to add miles to their life. See your tyre 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 tyre.
Tyres 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 centre as it is rotated. If runout is excessive, the wheel can be seen to wobble as it rotates.Back to top
The height of a tyre, measured from its rim to its outer tread.
The distance between the outside of a tyre’s sidewalls, not including any lettering or designs.
When the tyre is cornering, torque created at the road contact patch acts at a point somewhat to the rear of the actual wheel centre due to pneumatic trail. This has the same effect as positive caster and tends to force the wheel back to the straight-ahead position.
Tyres with the same aspect ratio, or relationship of section height to section width.
Numbers and letters moulded into the sidewall indicating the load-carrying capacity, load index and the speed at which the tyre 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 tyres, poor alignment and bent wheels.
The area of a tyre 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 centre line. The result is a feel of the car shaking from side to side.
The portion of a tyre between the tread and the bead. Protects the tyre against impacts with kerbs, etc. This is also where the sidewall markings can be found which tell you important information regarding the tyre.
In 1992, Michelin discovered how to incorporate this new reinforcing filler into the rubber compound of tyres. 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 tyre mounted on each side of an axle (two tyres per axle).
Special slits within a tread block that open as the tyre rolls into the contact patch then close, breaking the water tension on the road surface and putting rubber into contact with the road to maintain adhesion, increasing wet and snow traction.
The combination of tyre width, construction type, aspect ratio and rim size used in differentiating tyres.
The difference between the linear speed of the vehicle and the rotational speed of the tyre. For example, if a tyre 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 in which the wheel is travelling and the direction in which the vehicle is travelling.
Also called winter tyre; a special type of tyre 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 tyre indicating the range of speeds at which the tyre 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.
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 that a given size tyre can carry at a recommended air pressure.
A pattern for tightening the lug nuts when mounting the tyre and wheel assembly to the vehicle. This pattern assures uniform pressure, prevents misalignment and helps to keep the wheel centred.
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 the 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 tyre is rotating and helps to prevent flats.
A vehicle’s reaction to a driver’s steering input. Also the feedback that drivers get through the steering wheel as they make steering input.
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.
The way in which a tyre carcass is constructed. Radial structure tyres can be identified by the word radial or by the letter R and today account for the majority of vehicle tyres.
The various springs, shock absorbers and linkages used to suspend a vehicle’s frame, body, engine, and drive train above its wheels.
The 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 commercial vehicle tyres have a relatively small amount of natural rubber in their content.Back to top
Also called pneumatic tyre, 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 moulded into the sidewall of the tyre that describes the tyre’s size, including width, aspect ratio, rim diameter, load index and speed rating. Most designations use the P-Metric system.
A situation in which tyres 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 tyre 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 tyre.
The difference in distance between the front and rear of a pair of tyres mounted on the same axle.
The fronts of two tyres on the same axle are closer than the rears of the tyres.
The fronts of two tyres on the same axle are further apart than the rears of the tyres.
Also known as the Ackerman Angle. A vehicle’s wheels on the inside of a turn follow a smaller radius than the tyres 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 metres.
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 tyres on the same axle.
The friction between the tyres and the road surface; the amount of grip provided.
A state in which a vehicle bounces up and down abnormally.
That portion of a tyre 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 tyre comes new with 10/32nds of rubber, you have 8/32nds of usable rubber. Tyres must be replaced when the wear bars are visible at 2/32nds (1.58 mm).
The life of a tyre before it is pulled from service; mileage.
The tread section that runs around the circumference of the tyre separated by the tread grooves.
Narrow bands, sometimes called wear bars, that appear across the tread of the tyre when only 2/32 inch (1.58 mm) of tread remains.
The width of a tyre’s tread.Back to top
Operating a tyre without sufficient air pressure to support the weight of the vehicle with occupants and additional load; could cause failure of the tyre when heat is generated inside the tyre to the point of degeneration of components.
The handling characteristic in which the front tyres break loose because they are running a larger slip angle than the rear tyres. Also known as ploughing.
The 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 tyre designed to only rotate in one direction.
The weight of the parts of a vehicle not supported by its springs, including wheels and tyres, outboard brake assemblies, the rear axle assembly, suspension members, springs, shock absorbers and anti-roll bars.
Also known as Uniform Tyre Quality Grading Standards. A government-sponsored tyre information system that provides consumers with ratings (from AA to C) for a tyre’s traction and temperature. Treadwear is normally rated from 60 to 700.Back to top
A device that lets air in or out of a tyre. 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 maximises 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 tyre to minimize the noise generated by the tyre as it rolls.
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 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.Back to top
A vehicle’s tendency to stray or wander from its intended direction of travel as a result of steering abnormalities, worn tyres, suspension misalignment, cross winds or road irregularities.
Indicates how efficiently the tyre disperses water to combat aqua-planing, and how well it grips wet roads in low-speed driving.
The longitudinal distance from the centre of the front wheel to the centre of the rear wheel on the same side of the vehicle.
Small weights attached or secured to the wheel to balance the tyre and wheel assembly.Back to top
When the mounting face of the wheel directly aligns with the wheel’s centre line.
Michelin® Zero Pressure™ tyres feature a reinforced sidewall that is designed to support the weight of your car even after a loss of air pressure — even with no air in the tyre. Michelin® Zero Pressure Technology allows you to continue driving up to 50 miles at 55 mph, so you don’t have to change a tyre on the side of a busy motorway. Best of all, Zero Pressure Technology has been applied to some of the best-performing Michelin® tyres.
When tyres on the same axle are parallel; the fronts and rears of the tyres are equidistant.Back to top