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Plies (or ply): The reinforcing members of a tyre which are composed of layers of cord fabric and rubber that provide the strength to contain the air pressure needed to support a load and resist deflection.


Profile (also see Aspect Ratio): The height of the tyre sidewall expressed as a percentage of the tyres width.


PSI (pounds per square inch): Imperial measurement unit for air pressure.


Radial Tyre: The design of all modern car tyres. Development of the use of parallel carcass belts for sidewalls and crossed belts for the crown of the tyre.


Repairable Area:  Tyre Tread area where a puncture repair can be made to the British Standard BSAU159f .


Reinforced Tyres:  Tyre where the manufacturer has added extra strength by adding more plies into the side wall to handle more weight e.g. for heavier vehicles (i.e. SAAB 9-3s or Ford Galaxy’s Renault Laguna).


Remoulding: A recycling process where a tyre is buffed back to its casing, repaired and rebuilt using a fresh tread compound.


Retreading: This is the process of replacing the tread layer on a tyre. Usually reserved for commercial, agricultural and industrial tyres.


Rim: The metal edge of the wheel on which the bead is seated supporting the tyre.


Rim Size: The diameter of the rim (usually measured in inches and also known as the wheel size).


Rim Width: The Distance between the two opposite inside edges of the rim flanges.


Rolling Resistance: The energy required to keep a tyre moving at a constant speed. The lower the rolling resistance the less energy being used to keep the tyre moving.


Run-Flat: Tyres which allow a driver to continue a journey in the event of low or no pressure. Please note that Run-flats are designed to run for short distances and should be replaced as soon as possible.


Section Height: The height of the tyre from the rim to the outer tread.


Section Width:  Measurement of the tyre from side to side. This measurement excludes raised letters or any other additional sidewall items.


Service description: As well as Tyre Size Designation a tyre may be identified by a Service Description consisting of a load index (or two Load Indices in the case of single/dual fitments) and a Speed Symbol.


Shoulder: This is where the sidewall and the tread meet on the tyre.


Sidewall: This refers to the area between the bead and the start of the tread.


Silica: Reinforcing filler used in a rubber compound to provide higher tyre mileage and lower rolling resistance .


Sipes (also known as Blades): This refers to slits in the tread blocks which are designed to increase grip on winter and wet-weather tyres by moving water away from the tyre.


Snow Tyres: Tyres specifically designed to perform better in the snow.


Space Saving Tyre (also known as a “Mini” tyre): Smaller than the road tyres, this type of Tyre is designed to save space and reduce weight in the vehicle. A temporary measure to get you home these tyres should be changed as soon as possible, these tyres also have a lower maximum speed.


Speed Rating: The standardised index which is used to indicate the maximum speed a tyre can sustain carrying the specified load.


Specified load: Found in the load index under the conditions specified by the tyre manufacturer.


Steel rimmed wheels: The standard fit wheel for most cars, can be upgraded to alloy wheels.

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