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Tyre Glossary

Air Pressure Essentially - the amount of air inside the tyre. Measured in either pounds per square inch (psi) or bars. The correct pressure for tyres can usually be found in the vehicle handbook and often on the flap of your petrol tank.
Alignment Alignment essentially is the correct vertical alignment of a tyre. It is a process that ensures the suspension and wheels in association with the steering are in accordance with the manufacturer’s specification for the optimal way the wheels should be pointing.
Balancing Tyre balancing is a process to ensure that when the tyre and the wheel spin their weight is equally distributed.
Bar Metric Unit for measuring Air Pressure (1 bar = 6.8947 PSI).
Bead A ring of steel wire, within a rubber ‘wrapper’, that helps to hold the tyre to the rim.
Load Index This is a code that ranges from 0 to 279 that quantifies the maximum weight a tyre can bear at the speed indicated by the speed symbol under certain service conditions.
Pounds Per Square Inch (PSI) The imperial unit for air pressure.
Rim Diameter The diameter of the rim bead seats
Rim Size Distance between the two opposite inside edges of the rim flanges
Rim The metal edge of the wheel on which the bead is seated, enabling the tyre to be supported.
Rolling Resistance The energy needed to keep a tyre moving at a constant speed. A low rolling resistance means less energy is being used to keep a tyre moving.
Run-flats Run flat tyres enable vehicles to be driven, at reduced speeds for a limited time until they can be replaced.
Section Height Tyre height from rim to the outer tread.
Section Width The measurement of the tyre from side to side excluding any additional sidewall items such as raised letters.
Size Used to identify a specific tyre. It includes width, construction type, aspect ratio and rim size.
Speed Rating Speed rating to indicate the range of speeds at which a tyre can carry a load under a range of conditions. Ratings are categorised from A-Z.
Traction A term used to describe the force of friction between the drive wheel and the road.
Tread Depth The measurement between the top of the tread runner to the tyres deepest grooves. The legal limit for tread depth is a minimum of 1.6mm.
Tread Width Tread width is the portion of the tyres width that is covered by a tread pattern. (Measured in Millimetres)
Tread The part of the tyre that comes into contact with the road
Tread Wear Indicator Narrow bands in the tread grooves that provide a visual warning to a tyre needs changing, since they can only be seen if the tread has worn below the 1.6mm threshold.
Tyre Made of a mixture of rubber, chemicals, fabric and metal their job is to give the car traction on the road in a variety of conditions, and to cushion the car from shock.
Tyre Pressure This is the amount of air inside the tyre measured in PSI or in Bar. The correct pressure can be found in the vehicle handbook and usually on the inside of the petrol tank flap. This should be checked regularly as tyre pressure reduces gradually over time. Never inflate tyres beyond the maximum pressure specified in the vehicle manufacturer’s handbook.
Tyre Wall The area on the tyre where information about the tyre is displayed.
Under Inflation The condition that exists when there is not sufficient air pressure in a tyre.
Valve Allows the tyre to be inflated to the correct pressure. Valves are usually made of rubber, with a metal core assembly with a screw on dust cap. There are 2 standards lengths, short for most alloy wheels and long for steel wheels that have a plastic wheel trim.

Tyre inspection procedure for a claim