Tyre Glossary

Tyre Glossary
Title Description
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  to your petrol tank.
Alignment Alignment is a process that ensures the suspension  and  wheels in association with the steering are in accordance with the manufacturers specification for the optimal way the wheels should be pointing.
Aspect Ratio This is a way of expressing a tyre's height as a percentage of its section width. This figure is always found on the sidewall of the tyre.
Balancing Tyre balancing is a process to ensure that the when the tyre and the wheel spin their weight is equally distributed.
Bead A ring of steel wire, within a rubber ‘wrapper’, that helps to hold the tyre to the rim.
Casing This is the skeleton of the tyre sitting underneath the tread and sidewalls.
Cold Inflation Pressure This is the tyre pressure before the tyre has been able to heat up from driving.
Cold weather tyres Tyre designed to give better grip below temperatures of 7 degrees. Also known as winter tyres but snow tyres are something different.
Footprint The area of the tyre's tread that is in actual contact with the ground.
Innerliner In a tubeless tyre, the innerliner prevents air from seeping out of the tyre.
Bar Metric unit for air pressure (1 bar = 14.50326 psi).
Load Index This is a code  that ranges  from 0 to 279 that quantifies the maximum weight a tyre can bear at the spped indicated by the speed symbol under certain service conditions.
Low profile tyres A description of tyres that are quite ‘thin’ in comparison to the radius of the wheel.
Maximum Inflation Pressure The maximum pressure that a tyre can be inflated to.
Pounds per square inch (psi) The imperial unit for air pressure.
Rim The metal edge of the wheel on which the bead is seated enabling the tyre to be supported.
Rim Diameter The diameter of the rim bead seats.
Rim Width Distance between the two opposite inside edges of the rim flanges.
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.
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.
Section Width The measurement of the tyre from side to side excluding any additional sidewall items such as raised letters.
Shoulder Found where the sidewall and tread meet.
Sidewall The area between the bead and the start of the tread.
Sipes Slits in the tread designed to improve grip in wet conditions.
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.
Tyre Information Information on the recommended pressure, rim size and load capacity can be found in your vehicle handbook and sometimes on the inside sill of the drivers door.
Tread The part of the tyre that comes into contact with the road.
Treadwear 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.
Tread Width Tread width is the portion of the tyres width that is covered by a tread pattern.
Underinflation The condition that exists when there is not sufficient air pressure in a tyre.