| 4x4 tyres | Some 4x4 show the manufacturer's name and the tread pattern in white on the sidewall. These are either in solid white or outlined in white. On the product codes tyres that have these features are described as RWL (raised white letters) for solid white; and OWL (outline white letters) for the outline type. |
Tyre Glossary
| Active Suspension | Suspension-related term |
| Aerodynamic Drag | Steering-related term |
| Aftermarket | Products designed for the replacement market. Aftermarket tyres must be of the same specification but do not need to be the same brand that was fitted to the vehicle by the manufacturer. An exception to this rule is in the case of changing sizes, especially on 4x4s. |
| Alignment (Tracking) see also: Caster/Camber, Toe in |
The net result of steering and linkage adjustments on the plane of a wheel spin, affecting tyre performance and wear. Tracking adjustments should only be done by a qualified mechanic. Unnecessary alignment work, or "tracking", is one of the most common forms of overcharging by tyre depots. |
| All Season Tyres | Tyres designed to be used all year, in any weather. May have Winter tyre design, or winter tyre compound compromise. |
| Anti-Dive | Suspension-related term |
| Anti-Lock-Braking System | Braking-related term |
| Anti-Roll Bar | Suspension-related term |
| Aquaplaning | On a wet road, water building up in front of a moving tyre can lift the tyre away from the road, causing loss of control. |
| Aspect ratio see also: Profile |
The ratio of the sidewall to the width of the tyre tread expressed as a percentage. So a tyre of 220mm width with a sidewall height of 110mm would be a 50 Aspect Ratio, or 50 profile tyre. |
| Asymmetrical see also: Directional |
Tyre tread patterns which vary from one side of the tread to the other, ie, they are not symmetrical. If these tyres are non-directional they must be fitted with the outside sidewall on the outer face of the wheel. If they are also directional, they will also be specific to the left and right sides of the vehicle. |
| Axle Tramp | Suspension-related term |
| BS AU 159f | The British Standard for tyre repairs for vehicles used on the road. We carry out all tyre repairs to this British Standard. (see Tyre Repairs) |
| Balance Weights | The weights used for balancing. Used to be mostly lead but now being replaced by zinc alloy. On high performance cars with alloy wheels, where possible, we use "stick-on" weights positioned out of sight on the inside of the wheel. |
| Balancing | The process of trueing wheel/tyre spin to remove the slight differences in a tyre and wheel assembly, to account for wheel run out and imbalances in tyre production. This eliminates steering vibration. etyres does not charge extra for this service. |
| Balancing Beads / Compounds | Powder, or beads, added to commercial vehicle tyres to produce wheel balancing using the laws of physics to even out imbalances. |
| Ball Joint | Suspension-related term |
| Bead | The area of the tyre that is in contact with the wheel rim. The bead carries a multi-layer steel band and a shape that helps hold the tyre on the rim. |
| Beaded edge see also: Clincher Tyre |
This is a veteran tyre (antique cars) held in the rim by a rubber bead carried in a lip in the wheel rim. Its own pressure retains it in place. |
| Bias-belted Tyre | This is a development of the crossply tyre, using radial technology over a crossply style structure. Some American market tyres are still manufactured as bias-belted. |
| Brake Bias | Braking-related term |
| Brake Torquing | Braking-related term |
| Bushing | Suspension-related term |
| Butyl Liner see also: Tubeless |
A fine inner layer in a radial tyre (usually) that prevents sudden loss of air in the event of a puncture. |
| C3M | Michelin's computer controlled tyre manufacturing process allowing short production runs at very high levels of conformity. |
| Calendaring | Part of the tyre manufacturing process. |
| Camber see also: Alignment |
The deviance from the vertical of the tyre centre line when the vehicle is at its normal ride level. Incorrect camber may cause uneven tyre wear. |
| Cap Band | This layer of nylon protective material applied to some high performance and SUV tyres to prevent delamination. |
| Carbon Black see also: Silica |
Rubber is grey in colour, Carbon Black is added as a filler, to provide a uniform colour, and to increase wear resistance. |
| Carbon Fiber see also: Carbon Black |
Composition-related term |
| Carcass see also: Casing |
The body of the tyre onto which the sidewall and tread are built. |
| Casing see also: Carcass |
The body of the tyre onto which the sidewall and tread are built. |
| Caster see also: Alignment |
The angle of inclination of the spin axis and to the vehicle in a vertical aspect. This retains the steering wheels in an "ahead" position. |
| Center Differential | Drive-related term |
| Clincher Tyre see also: Beaded edge |
This is a veteran tyre (antique cars) held in the rim by a rubber bead carried in a lip in the wheel rim. Its own pressure retained it in place. |
| Compliance | Suspension-related term |
| Contact Patch see also: Footprint |
The area of tyre tread in contact with the road at any given time. This varies during acceleration, braking and cornering. It can be affected by tyre pressure, temperature, rubber compound, and tread design. |
| Conti SSR see also: Run Flat |
Continental's run flat tyre system with self supporting sidewalls. |
| Control Arm | Suspension-related term |
| Cross-ply Tyre see also: Diagonal Tyre / Bias belted |
The replacement for the "clincher". This is the bias-belted or crossply tyre which has a steel bead wire to retain the tyre on the rim, and a series of cross ply carcass strength. |
| DOT Codes | The US Government coding (Department of Transportation) given to tyre factories. This data can help to identify the place and date of origin of the tyre. Dot Codes are available on the Internet. |
| De Dion Suspension | Suspension-related term |
| De-vulcanisation see also: Vulcanisation |
The chemo-mechanical process which causes the tyre compound to break down, often through heat build-up due to under-inflation. Can cause tyre failure. Also a process used in recycling vulcanised rubber. |
| Deformation | The "give" in a tyre interacting with the road and the driver input. A tyre with little give will handle differently from a tyre with lots of give. A tyre should have a compromise for the best performance on the road. |
| Delamination see also: Tread separation |
The process where a tyre that is faulty, or has been run under-inflated, may break down, causing its tread layer to become separated from the casing. |
| Diagonal Tyre see also: Crossply |
The replacement for the "clincher". The crossply tyre has a steel bead wire to retain the tyre on the rim, and a series of cross ply belts to give the carcass strength. |
| Differential | Drive-related term |
| Directional see also: Asymmetrical |
A tyre with a tread pattern that must be fitted in an indicated orientation. Often a chevron shaped pattern which assists the removal of water under the tyre. |
| Disc Brakes | Braking-related term |
| Disposal charge | A fee charged by many tyre depots to pay for the cost of disposing of the scrap tyre. etyres does not make a charge for this disposal, which we carry out in an environmentally friendly way. |
| Dive | Braking-related term |
| Driveline | Drive-related term |
| Drivetrain | Drive-related term |
| Drum Brakes | Braking-related term |
| E Marking | All car tyres sold from 1st July 1997 must carry an 'E' marking. They certify that the tyre complies with the dimensional, performance and marking requirements. |
| Economy | A new tyre of fair quality that we sell at a lower price than Mid Range. Logically, the performance of this range will also be lower. |
| Euphori@ see also: Run Flat |
Pirelli's Run Flat system. |
| Fabric see also: Textiles |
The materials used in the tyre belt are woven and will be constructed from a blend of textiles and fine wires. |
| Final-Drive Ratio | Drive-related term |
| Fitting; Front or Rear | When replacing car tyres the ideal method would be to change all four, thus maximising the road holding and evenness of grip. |
| Flywheel | Drive-related term |
| Footprint see also: Contact Patch |
The area of tyre tread in contact with the road at any given time. This varies during acceleration, braking and cornering. It can be affected by tyre pressure, temperature, compound and tread design. |
| Four-Wheel Drift | Steering-related term |
| Four-Wheel Steering | Steering-related term |
| G | Steering-related term |
| Grooves | Lateral - drains water to sides of the tyre. Circumferential - evacuates water to the rear of the tyre or "stores" it. The number of grooves increases as the tyre width increases. |
| Half-Shaft | Drive-related term |
| Handling | Steering-related term |
| Harmonics | An annoying vibration and audible noise which can cause discomfort for the occupants. This is a big issue for car and tyre manufacturers at the design stage. |
| Heel-and-Toe | Braking-related term |
| Heim Joint | Suspension-related term |
| Hotchkiss Suspension | Suspension-related term |
| Hysterisis | The resistance to deformation of the rubber in a tread block. The level of hysterisis in any given tyre dictates the heat it will generate in use, and therefore the rate at which it will deteriorate. High hysteresis is good as it helps the tyre resist "slip". |
| Independent Suspension | Suspension-related term |
| Jounce see also: Rebound |
Suspension-related term |
| Jounce Bumperan | Suspension-related term |
| Land Sea ratio | The ratio of tyre tread in contact with the road and the voids designed for removing water. Tread pattern blocks equate to land, grooves equate to sea. |
| Lateral Acceleration | The forces acting on a tyre to pull it sideways during cornering. |
| Lateral Link | Suspension-related term |
| Leading Link | Suspension-related term |
| Leaf Spring | Suspension-related term |
| Lift-Throttle Oversteer | Steering-related term |
| Limited-Slip Differential | Drive-related term |
| Live Axle | Drive-related term |
| Load Rating | This is shown on the sidewall of the tyre to indicate the maximum load the tyre is rated for. |
| Locking bolt see also: Also locking bolt key |
A security device to prevent the theft of (usually) alloy wheels. Typically one per wheel is fitted. If your vehicle has locking bolts it is important not to loose the "key". However, if you have lost the "key" we can usually overcome the problem, but we do make a charge for this. Price on application. |
| Lockup | Braking-related term |
| Lockup Differential | Drive-related term |
| Lockup Torque Converter | Drive-related term |
| M+S see also: Snowflake |
Mud and Snow tyre: A wide range of which are available from etyres. |
| MIRS | Pirelli's computer controlled tyre manufacturing process, which allows short production runs at very high levels of conformity. |
| Major Repair see also: Minor Repair |
A major repair is where a damaged tyre can be repaired using a reinforced internal patch and a Hot Vulcanisation process. More common on Commercial, agricultural and earthmover tyres but also used on some car tyres. |
| Mid Range tyre | A new tyre of fair quality that we sell at a lower price than the main brands of Bridgestone, Firestone, Michelin, Pirelli, etc. Logically, the performance of this range will also be lower. |
| Mu | The coefficient of the average grip of a tyre on a wet surface. A specification used in tyre design and testing. |
| Multi-purpose Off Road Tyre | Grooved at 35 per cent with 8 - 12 mm grooves, few sipes. Looks similar to a conventional car tyre. |
| Multilink Suspension | Suspension-related term |
| Natural Rubber see also: Synthetic Butyl Rubber |
Used in tyre construction, but not the best material to provide grip. |
| Neutral Steer | Steering-related term |
| Nitrogen | An alternative to air for inflating tyres. Nitrogen molecules are larger than those of oxygen and so are less susceptible to osmotic loss through the tyre casing. Tyres therefore stay at the correct pressure for longer. Being inert there is also the argument that nitrogen can reduce deterioration of the tyre from inside. Can also assist in maintaining an even temperature. However these benefits are marginal because air already contains 78% nitrogen. |
| Nut/Bolt Torque | The correct "tightness" for wheel nuts/bolts. See chart in Caring For Your Tyres. |
| OEM | Original Equipment Manufacturer - so a tyre may be from an OEM, but not be OE fit. |
| OWL | A term to describe; Outline White Letters which are a sidewall marking of certain 4x4 tyres |
| On-Center Feel | Steering-related term |
| Opposite Lock | Steering-related term |
| Original Equipment (OE) | The original brand of tyre or battery that was fitted by the car manufacturer. There may be more than one OE brand fitment. |
| Oversteer | When the driver corners, the rear wheels lose grip and the rear of the car starts to slide sideways. |
| PAX see also: Run Flat |
Michelin's run flat technology that requires special wheel rims and Tyre Pressure Monitoring System (TPMS). |
| PSI | Pounds per Square Inch |
| Polar Moment of Inertia | Steering-related term |
| Profile see also: Aspect ratio |
The ratio of the sidewall to the width of the tyre tread. Expressed as a percentage ie. a tyre of 220mm width with a sidewall height of 110mm would be a 50 Aspect Ratio, or 50 profile tyre. |
| Progressive-Rate Spring | Suspension-related term |
| Puncture Treatments see also: Sealants |
A range of aftermarket tyre additives that can be used to minimise air loss in the event of a puncture. Some offer "permanent" repairs, others offer a "get you home" repair. |
| RWL | A term to describe; Raised White Letters which are a sidewall marking of certain 4x4 tyre |
| Rack-and-Pinion | Steering-related term |
| Radial Tyre | This is the carcass design originally developed by Michelin using parallel carcass belts for the sidewalls and crossed belts for the crown of the tyre. All modern car tyres are radial. |
| Rebound see also: Jounce |
Suspension-related term |
| Recirculating Ball | Steering-related term |
| Regrooving | The process of cutting new grooves into worn tread to extend the life of truck tyres . An illegal operation on car, 4x4 and light commercial tyres. |
| Remoulding | A recycling process where a tyre is buffed back to its casing, repaired and rebuilt using fresh tread compound. We only sell remoulded tyres in very exceptional cases. |
| Repairable Area | The area of the tyre tread where a puncture repair can be made to British Standard BSAU 159. A free "repairable area tread gauge" can be downloaded from this website, here, for your use to assess whether a puncture may be repairable. |
| Retreading | The process of replacing the tread layer on a tyre. Generally reserved for commercial, agricultural and industrial tyres. |
| Ride Height | Suspension-related term |
| Ring-and-Pinion Gear | Steering-related term |
| Road tyre | Generally designed with a land/sea ratio of 30 per cent void. 6 - 9mm deep. |
| Roadholding | Steering-related term |
| Roll | Steering-related term |
| Rolling Resistance | The amount of energy required to overcome the static mass of the tyre. This can be affected by design, load and pressure. |
| Run-Flat see also: PAX, SST, Eufori@, Tyron |
A tyre designed to run at low or no pressure to enable the driver to reach a place of safety, or even complete the journey. Read more here. |
| SST | Dunlop "run-flat" system. Initial letters stand for Self Supporting Technology. |
| Scrub Radius | Steering-related term |
| Sealants see also: Puncture treatments |
A range of aftermarket tyre additives that can be used to minimise air loss in the event of a puncture. Some offer "permanent" repairs, others offer a "get you home" repair. |
| Semi-Elliptic Leaf Spring | Suspension-related term |
| Semi-Trailing-Arm Suspension | Suspension-related term |
| Series see also: Aspect Ratio |
Tyre-related term |
| Shock Absorber | Suspension-related term |
| Shoulder area | The edge of the tread where it meets the sidewall. Its design is key to cornering characteristics on road tyres and important in attaining grip on off-road tyres. |
| Sidewall | The side of the tyre between the rim and the tread. This carries all the tyre identification data, load rate, speed rating and manufacturing data. |
| Silica see also: Carbon Black |
A filler obtained from sand and used to improve grip in the wet and extend tyre life. |
| Single-Rate Spring | Suspension-related term |
| Sipes | Narrow slits in the tread blocks designed to pump water away and to create more leading edges to increase grip in winter and wet-weather tyres. (See Reading Your Tyre) |
| Skidpad | A circular area used to measure roadholding. |
| Slip | That element of the deformation of the tread block in cornering, or braking, before it breaks away. |
| Slip Angle | Steering-related term |
| Snowflake see also: M+S |
USA and Canada: This additional marking on an M+S tyre shows that the tyre meets legally prescribed test criteria and advises that it has good winter properties. |
| Space saver | A spare tyre of a smaller size than the road tyres. The purpose of the reduced size is to save space and reduce weight. Designed to get you home, these tyres have a slower maximum speed and are designed to be only used on a temporary basis . These tyres have been banned in New Zealand. Certain cars, such as Porsche, use an un-inflated spare accompanied by a small electric compressor. |
| Specialist Off Road Tyre | Land Sea ratio of 40 per cent. Usually grooved to 15mm depth, very blocky tread pattern. |
| Speed Rating | The maximum continuous speed the tyre is rated for. (See Reading Your Tyre) |
| Sports tyre | Generally the Land Sea ratio is higher in a sports tyre and there are few or no sipes. |
| Squat | Steering-related term |
| Standing Wave | A wave of deformation in front and behind the contact patch of a rolling tyre. Too great a standing wave creates heat build-up and tyre de-vulcanisation. |
| Steering Axis | Steering-related term |
| Steering Feel | Steering-related term |
| Steering Geometry | Steering-related term |
| Strut | Suspension-related term |
| Sulphur | Transforms rubber from an elastic to plastic state to be moulded and vulcanised. |
| Synthetic Butyl Rubber (SBR) see also: Natural Rubber |
60 per cent of rubber used in tyres is synthetically manufactured from crude oil. SR has a high level of Hysterisis. |
| Textiles see also: Fabric |
The materials used in the tyre belt are woven and are constructed from a blend of textiles and fine wires. |
| Toe in/out see also: Alignment |
The deviation of the centreline of the tyre from a true fore and aft position. Too much "toe" will result in excessive and uneven tyre wear. |
| Toe-Control Link | Suspension-related term |
| Toe-In | The intentional non-parallel orientation of opposing wheels. |
| Torsion Bar | Suspension-related term |
| Torsional distortion | The forces creating a twisting distortion in the sidewall during acceleration and braking. |
| Traction Control | Braking-related term |
| Trailing Arm | Suspension-related term |
| Trailing Link | Suspension-related term |
| Tread separation see also: Delamination |
The process where a tyre that is faulty, or has been run under-inflated, may break down, causing its tread layer to become separated from the casing. |
| Treadwear Indicator | A bar of rubber moulded into the base of the tread, positioned in at least three points around the tyre. When level with the tread pattern the tread is worn down to a point where the tyre should be replaced. |
| Tubed see also: Tubeless |
A tubed tyre requires the use of an inflatable inner tube. Such tyres are susceptible to rapid deflation when punctured. |
| Tubeless see also: Tubed |
A tubeless tyre is usually a radial tyre with a thin butyl rubber liner that seals around penetrations helping to prevent instant loss of pressure in the event of a puncture. |
| Tyre Pressure | Tyre pressure is the measurement of the volume of air inside the tyre when it is inflated. Formally measured in pounds per square inch (psi) now measured in bar. (1 bar = 14.503774 psi) . Pressure will gradually reduce and therefore regular checking and topping-up is necessary to maintain the vehicle manufacturers recommended pressure. (See vehicle owners manual). Never inflate a tyre to a greater pressure than the maximum that is indicated on the sidewall of the tyre. |
| Tyre Pressure Monitoring System (TPMS) | A method of monitoring tyre pressure from inside the car whilst the vehicle is in use. Usually a RFID device inside the wheelwell, or attached to the tyre, sends data to an onboard display to alert the driver about pressure loss in the tyre. It may also be based on the differential in the vehicle's ABS system, but the latter, though cheaper, is thought to be unreliable. |
| Tyre Repairs | Tyre repairs should only be carried out by specially trained personnel using professional equipment. |
| Tyron see also: Runflat |
An bolt-on emergency runflat system ideally suited for caravans and trailers, but can also be fitted to cars. Use of TPMS is advised. |
| Understeer | When the car "fails" to respond to steering and ploughs straight on. |
| Universal Joint | Drive-related term |
| Valve | Usually made of rubber, with a metal core assembly and a plastic, screw-on dust cap. Allows the tyre to be inflated to the correct pressure. Available in two standard lengths, short for most alloy wheels, long for steel wheels which have a plastic wheel-trim. Certain types of commercial vehicle, such as the Ford Transit, require a high pressure rubber valve. Many high performance cars are fitted with metal "bolt-in" valves. etyres prices always include supplying and fitting a new rubber valve. For metal valve prices please phone our call centre on 0800 028 9000. |
| Valve cap see also: Dust cap |
A plastic, screw-on, cap to prevent dirt from entering the valve. |
| Viscous Coupling | Drive-related term |
| Vulcanisation see also: De-vulcanisation |
The process of cooking "green" rubber compounds to create a hard plastic rubber that retains its form for tyre use. |
| Vulcanisation (Cold) | Repairs using the cold vulcanisation process are only permitted if the tyre has suffered superficial penetration damage in the tread area and only if the damage does not extend beyond 6 mm - measured on the inside of the tyre. The hole itself must be filled and the damage on the inside of the tyre sealed off. Inserting an inner tube without repairing the damage is not permitted. Sealing the damaged area by means of a puncture spray should only be regarded as a temporary measure in an emergency. (See Tyre Repairs) |
| Vulcanisation (Hot) | Hot Vulcanisation is the process of heating a tyre to retread or carry out a major repair. Damage that extends to the bead, belt or beyond must be repaired by hot vulcanisation.( See Tyre Repairs) |
| Wheel Hop | Suspension-related term |
| Wheel Size see also: Diameter |
Wheel Size this is the actual diameter of the wheel. This is usually measured in inches however, as few vehicles manufacturers still use metric wheels. |
| Width | Width is the measurement of the lateral flat part of the tread. |
| Winter Tyres see also: Snow Tyres |
A misnomer as this implies use in snow and ice Winter tyres should ideally be used at temperatures below 7 degrees Celsius. We sell a range of winter tyres and pre-fitted tyre/wheel assemblies that are ideal for Continental and Scandinavian use. |
| Yaw | Steering-related term |
| Zero-Offset Steering | Steering-related term |
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