Blackcircles.com Tyre Glossary P-S
a-c d-o p-s t-z Glossary Home
Plies: 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 BSAU 159
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. (ie 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 2 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 (link)
Silica: reinforcing filler used in a rubber compound to provide higher tyre mileage and lower Rolling Resistance
Sipes: (also known as Blades) (link) 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 standardized index which is used to indicate the maximum speed a tyre can sustain carrying the
Specified load 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