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A

Air Pressure

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.

Airtight Synthetic Rubber

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.

Alignment

When all wheels on the vehicle are adjusted so that they are pointed in the optimum direction relative to the road and each other.

All-season high-performance tyres

Tyres that deliver a measure of traction on snow and ice without sacrificing dry performance driving capabilities.

All-season tyres

Tyres that provide a good balance of traction in rain or snow with good tread life and a comfortable, quiet ride.

All-season traction

Indicates the tyre’s ability to provide a balance of traction in wet, dry and winter conditions.

APS

An advanced silica-based winter rubber compound that helps provide flexibility where the tread surface makes contact with the road.

Aqua-planing

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.

Aramid

A synthetic fabric used in some tyres that is (pound-for-pound) stronger than steel.

Aspect Ratio

The relationship of a tyre’s sidewall height to its section width.

Asymmetrical Tread Design (AD)

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.

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B

Balance/Imbalance

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.

Banded At Zero Technology™

Michelin® BAZ Technology™ uses spiral-wrapped nylon strips applied in the tread area atop the steel belts at zero degrees. BAZ Technology™ opposes centripetal forces that can cause tyre distortion at high speeds1. BAZ Technology™ optimises high-speed handling and durability.

Bead

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.

Bead Chafer

A key component of the tyre that is the contact point between the tyre and the wheel, designed to withstand the forces that the wheel puts on the tyre during mounting as well as the dynamic forces of driving and braking.

Bead Filler

Responsible for transferring propulsion and braking torque from the wheel rim to the road surface contact area.

Bead Tension Structure

Two sidewall plies wrapped around each bead wire in opposite directions providing lateral stability but also flex to absorb road irregularities.

Belt

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.

Bias-Ply

A type of tyre with crossed layers of ply cord running diagonally to the centre line of the tread.

Bolt Circle

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.

Braking Torque

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 releasing the brake.

Breakaway

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.

Butyl Rubber

Synthetic rubber used to create today’s tyres. It is virtually impenetrable to water and air.

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C

C3M Technology™

A manufacturing process that permits the precise placement of different tyre components and multiple rubber tread compounds.

Camber

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.

Camber Thrust

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.

Carbon Black

This is a reinforcing filler which, when incorporated into the tyre rubber compound, gives it a high resistance to wear.

Carcass

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.

Carcass Ply

Made up of thin textile fibre cables bonded into the rubber. These cables are largely responsible for determining the strength of the tyre.

Carrying Capacity

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.

Caster

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.

Centerline

An imaginary line down the centre of the vehicle. Alignment tracking is measured from this line.

Centrifugal Force

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.

Cold Inflation Pressure

The amount of air pressure in a tyre, measured in pounds per square inch (psi) before a tyre has built up heat from driving.

Comfort Control Technology™

Uses precision manufacturing to ensure an ultra-high level of tyre uniformity, while also employing powerful proprietary tread design software to minimise tread acoustics.

Compliance Cushion

An added rubber tyre component between the tread and belt that absorbs road irregularities for a smoother ride.

Contact Patch

The area in which the tyre is in contact with the road surface. Also called footprint.

Cord

The strands of fabric forming the plies or layers of the tyre. Cords may be made from polyester, rayon, nylon, fibre-glass or steel.

Cornering Force

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.

Cross Z-Sipes Technology

A sipe pattern that provides lateral and longitudinal stiffness within the tread block.

Crown Plies

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.

Curb Weight

Weight of a production vehicle with fluid reservoirs (including fuel tank) full and all normal equipment in place, but without driver or passengers.

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D

Deflection

The tread and sidewall flexing where the tread comes into contact with the road.

Directional Stability

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.

Dog Tracking

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.

DOT Markings

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

Drift refers to a vehicle deviating from a straight-line path when no steering input is given. Also called pull.

Duals

tyres placed side by side on an axle to increase both carrying capacity and traction capability; four tyres across an axle.

Dual Tread Compounding

Employs two compound types across the tread, the outside for dry traction and the inside for wet traction.

DURABLACK®

A compound technology that allows a tyre’s sidewall to stay a rich black during the entyre life of the tyre.

DuraGuard Technology™

Includes various features, such as two sidewall plies and high-strength steel belts under the tread.

Durometer

An instrument used to measure hardness. Specific to tyres, a durometer typically measures the hardness of the tread compound. Durometer can also refer to the hardness result, as in: The tyre’s durometer is 60.

Dynamic Balance

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.

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E

Eccentric Mounting

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.

ECE Symbol

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.

Extra Load

tyres that are rated to carry a higher load by virtue of having a maximum inflation pressure higher than the standard maximum.

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F

Filament at Zero

Individual, spiral-wrapped nylon or aramid/nylon reinforcing filaments can be precisely placed in specific portions or across the entyre tread area atop the steel belts banded at zero degrees. Not only does this help retain tyre shape, but it also enhances ride quality and steering precision.

Fore-and-Aft Weight Transfer

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.

Four-wheel-drift

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.

Free Radius

The radius of the tyre/wheel assembly that is not deflected under load.

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G

Green X®

The Michelin® Green X® label guarantees a level of energy efficiency among the highest in the market and reduced CO2 emission while maintaining all the legendary Michelin advantages of long wear, safety and other performances.

Groove

The space between two adjacent tread ribs; also called tread grooves.

Gross Axle Weight Rating (GAWR)

The maximum weight that can be distributed among the tyres on a given axle.

Gross Vehicle Weight (GVW)

The weight of the vehicle and its contents (fluids, passengers and cargo).

Gross Vehicle Weight Rating (GVWR)

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.

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H

High Flotation Sizing System for Light Commercial Vehicles

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.

High Modulus Undertread™

Layer of rubber below grooves that anchor the tread blocks to the casing plies for increased grip, steering response and optimal handling.

High-performance tyres

Also called maximum performance or ultra-high-performance, etc. They offer a superior degree of handling, grip and cornering ability than standard tyres. High-performance tyres are also rated for operation at higher speeds than non-high-performance tyres.

Hub-centric

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.

Hysteresis

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.

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I

Indentation

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.

Inflation

The act of putting air into tyres.

Inner liner

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.

Interlocking Sipes

S-shaped sipes that interlock, creating greater sipe length for extra tractive grip.

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K

Kilopascal (kPa)

The metric unit for air pressure. One psi is equal to 6.9 kPa.

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L

Lateral runout

Side-to-side wobbling of a wheel as it rotates; a shimmy.

Lateral weight transfer

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.

Life Maximised Adherence™ Compounding

A street-optimised compound for predictable handling, sustained levels of grip and excellent traction throughout the tyre’s life.

Light commercial vehicle

Automotive industry term for smaller vans, pick-ups, passenger vans or estate cars/4x4s.

Linearity

A term used to characterise steering response.

Load-carrying capacity

Indicates how much weight a tyre is certified to carry at maximum inflation pressure.

Loaded radius

The measurement in inches from the wheel axle centre line to the ground when the tyre is properly inflated for the load.

Loaded section height

The height of the section of the tyre that is making contact with the road.

Load index

An assigned number ranging from 0 to 279 that corresponds to the load-carrying capacity of a tyre.

Load range

Defines a range of maximum loads that tyres can carry at a defined pressure.

Lug-centric

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.

Luxury performance touring tyres

Generally designed for luxury saloon cars, this breed of tyres blends performance handling with a comfortable, smooth ride.

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M

M+S, M/S or M & S

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.

Match mounting

Technique that matches the harmonic high point of a tyre with a low point of the wheel to ensure optimal ride performance.

Maximum inflation pressure

The maximum air pressure to which a cold tyre may be inflated; can be found moulded onto the sidewall.

Metric tyre size system

One system used to describe a tyre’s size. It is the standard system of the ETRTO(European tyre and Rim Technical Organisation).

Michelin Man™

The Michelin Man™ has represented the Michelin corporation for more than 100 years.

Misalignment

The result of your vehicle’s front and/or rear suspension not being properly aligned.

Mounting

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.

MSRP

Manufacturer's Suggested Retail Price.

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N

Negative camber

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.

Negative offset

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.

NHTSA

National Highway Traffic Safety Administration.

Nominal Rim Diameter

The diameter of a tyre rim, given in nearest whole numbers (e.g. 38 cm/15 in.).

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O

Offset

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.

Off-the-car balancing

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.

Original Equipment

Tyres selected by a vehicle manufacturer that best match tyre performance to vehicle performance characteristics. Also known as OE.

Overall diameter

The diameter of the inflated tyre, without any load.

Overall width

The distance between the outside of the two sidewalls, including lettering and designs.

Over-inflation

Too much air in the tyre, resulting in premature wear in the centre of the tread.

Over-steer

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.

Oxidation

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.

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P

20 Pence Test

A simple, commonly-used test to check the proper tread depth on a tyre with a twenty pence piece. To learn how to use the 20 pence test, click here.

PAX System™

The Michelin® PAX™ System is a new run-flat technology that combines a unique tyre, wheel, support ring, tyre-pressure monitoring system and specially formulated gel to enable continued mobility after a sudden loss of inflation pressure. The system is designed for operation at 90 km/h for a range up to 200 km. When in normal (inflated) operation, Michelin® PAX™ System tyres enhance road handling and driving comfort, plus reduce rolling resistance.

Plus-sizing

An option allowing drivers to customise their vehicles by mounting low-profile tyres on wider rims (2.5-5 cm/one or two inches greater in diameter), usually enhancing vehicle appearance, handling and performance.

Ply

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.

P-metric

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.

Pneumatic tyre

A tyre designed to be filled with air.

Positive camber

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.

Positive caster

Alignment setting when the steering axis is inclined rearwards at the top.

Positive offset

The mounting face of a wheel is toward the wheel’s street side, moving the tyre and wheel assembly in towards the vehicle.

Proprietary Blended Compounding

Technology that creates a uniform compound blend that helps to provide outstanding all-around performance in wet and dry conditions.

PSI

Abbreviation for pounds per square inch, which is the car industry’s measurement of the pressure in a tyre.

Pull

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.

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R

Radial ply tyre

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.

Radial XSE® Technology

A revolutionary technology that utilises silica in the rubber compound to enhance a tyre’s wet traction, snow traction and rolling resistance.

R-Compounding

A racing-derived compound optimised for on-track performance and designed for maximum dry grip and repeated heat cycles.

Revolutions Per Mile (RPM)

Also called rpm. The measured number of revolutions for a tyre travelling one mile. This can vary with speed, load and inflation pressure.

Ribs

A pattern of tread features aligned around the circumference of a tyre. There are usually multiple ribs across the tread area of a tyre.

Ride height

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.

Rim

That portion of a wheel to which a tyre is mounted.

Rim diameter

The diameter of the rim bead seats supporting the tyre.

Rim Drop

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.

Rim flange

Surface of the rim of the wheel that contacts the side of the tyre bead.

Rolling circumference

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.

Rolling resistance

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.

Rotation

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 9,000-13,000 km) is a simple way to add km to their life. See your tyre warranty for more information on recommended rotation.

Rubber compound

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.

Run Flat Technology

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.

Runout

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.

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S

Section height

The height of a tyre, measured from its rim to its outer tread.

Section width

The distance between the outside of a tyre’s sidewalls, not including any lettering or designs.

Self-aligning torque

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.

Series

tyres with the same aspect ratio, or relationship of section height to section width.

Service description

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.

Shimmy

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.

Shoulder

The area of a tyre where the tread and sidewall meet.

Side-To-Side Wobbling

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.

Sidewall

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.

Silica

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.

Silica Tread Compound

A compounding of silica with a specially formulated synthetic elastomer for exceptional grip on cold and wet surfaces, as well as reliable durability.

Singles

One tyre mounted on each side of an axle (two tyres per axle).

Sipes

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.

Size

The combination of tyre width, construction type, aspect ratio and rim size used in differentiating tyres.

Slip

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.

Slip angle

The difference between the direction in which the wheel is travelling and the direction in which the vehicle is travelling.

Speed rating

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.

Sprung weight

The parts of a car that are supported by its springs, including the frame, engine and body.

Squirm

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.

Stability

Situation in which the driver maintains control of the vehicle.

Staggering

A staggered fitment is putting larger wheels on the back of your vehicle than the front of your vehicle.

Standard load

The amount of weight that a given size tyre can carry at a recommended air pressure.

Star pattern

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.

Static balance

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.

Static loaded radius

Distance from the wheel axis of rotation to the supporting surface at a given load and stated inflation pressure.

Steel belt

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.

Steering response

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.

Steering system

The entyre mechanism that allows the driver to guide and direct the vehicle; includes the steering wheel, steering column, steering gear, linkages and wheel supports.

Step groove

A design feature at the base of the groove that generates an additional gripping mechanism in deeper snow.

Stress Equilibrium Casing™

A radial casing design that more evenly distributes the forces of acceleration, cornering and braking throughout the contact patch, allowing for design enhancements in the shoulder and the use of softer, better gripping compounds.

Structure

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.

Supporting Knobs Technology

Small bumps in the shoulder grooves help to provide lateral block rigidity.

Suspension

The various springs, shock absorbers and linkages used to suspend a vehicle’s frame, body, engine, and drive train above its wheels.

Symmetrical Tread Design

The uniform tread pattern on both sides of the tread for better performance in specific conditions and on specific roads.

Synthetic rubber

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.

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T

T & RA

tyre and Rim Association.

Tensile Strength

An object’s resistance to stretching or breaking when placed in tension. Steel belts in a tyre are characterised and compared based on their tensile strength.

tyre

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.

tyre Designation

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.

tyre Mixing

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.

tyre Placard

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.

tyre Pressure Gauge

Tool used to properly measure the air pressure in a tyre.

Toe

The difference in distance between the front and rear of a pair of tyres mounted on the same axle.

Toe-In

The fronts of two tyres on the same axle are closer than the rears of the tyres.

Toe-Out

The fronts of two tyres on the same axle are further apart than the rears of the tyres.

Toe-Out Turns

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.

Torque

Turning or twisting effort, usually measured in lb-ft or Newton metres.

Torque-Locking Sipes

Sipes with vertical undulation (into tread block) for added rigidity during cornering.

Torsion Bar

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.

Touring tyres

Generally offer increased tread life, comfort and all-season traction.

Track

The distance between the outside tread edges of two tyres on the same axle.

Traction

The friction between the tyres and the road surface; the amount of grip provided.

Tramping

A state in which a vehicle bounces up and down abnormally.

Tread

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.

Tread Buffing

Scraping rubber off the tread. Also known as shaving.

Tread Depth

If a tyre comes new with 7.6mm of rubber, you have 6mm of usable rubber. tyres must be replaced when the wear bars are visible at 1.6mm.

Tread Life

The life of a tyre before it is pulled from service; mileage.

Tread Rib

The tread section that runs around the circumference of the tyre separated by the tread grooves.

Treadwear Indicator

Narrow bands, sometimes called wear bars, that appear across the tread of the tyre when only 1.6mm of tread remains.

Tread Width

The width of a tyre’s tread.

Tri Side-by-Side Compounding

A process that makes it possible to precisely place three different types of rubber compounds across the tread of a tyre.

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U

Ultra-Low Profile Technology

A specialised sidewall shape, bead area and bead compound that enhances the durability and mountability of tyres with very short sidewalls.

Under-inflation

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.

Under-steer

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.

Under-tread

The material between the bottom of the tread rubber and the top layer of steel belts; acts as a cushion that enhances comfort.

Uni-Directional Tread

Also known as directional tread, this is a tyre designed to only rotate in one direction.

Unsprung Weight

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.

UTQGS

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.

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V

Valve

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.

Variable Contact Patch

A system that maximises the contact patch area during cornering through a combination of asymmetrical tread patterns and underlying belts.

Variable Integrated Pitch

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.

Variable Thickness or Bi-directional Sipe

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

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.

Viscous Planing

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.

Vulcanization

The irreversible process of heating rubber under pressure to improve its strength and resilience.

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W

Wander

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.

Wet traction

Indicates how efficiently the tyre disperses water to combat aqua-planing, and how well it grips wet roads in low-speed driving.

Wheelbase

The longitudinal distance from the centre of the front wheel to the centre of the rear wheel on the same side of the vehicle.

Wheel weights

Small weights attached or secured to the wheel to balance the tyre and wheel assembly.

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Z

Zero offset

When the mounting face of the wheel directly aligns with the wheel’s centre line.

Zero Pressure™Technology

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 80 km at 80 km/h, 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.

Zero toe

When tyres on the same axle are parallel; the fronts and rears of the tyres are equidistant.

Zig Zag Sipes™ Technology

A zig-zag shaped, normally horizontal sipe that flexes and bites into the snow to help provide reliable cold-weather traction.

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