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Glossary of Tyre Terms

TyresOnTheDrive simplifies the most common tyre jargon

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Glossary

A

Air pressure

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 that the suspension and wheels, in association with the steering, are in accordance with the manufacturer’s specification for the 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.

B

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 air pressure. (1 bar = 14.50326 psi)

Bead

A ring of steel wire within a rubber wrapper that helps to hold the tyre to the rim.

C

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

Tyres designed to give better grip below temperatures of 7 degrees. Also known as winter tyres.

F

Footprint

The area of the tyre's tread that is in contact with the ground.

I

Inner liner

In a tubeless tyre, the inner liner prevents air from seeping out of the tyre.

L

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.

Low profile tyres

A description of tyres that are quite ‘thin’ in comparison to the radius of the wheel.

M

Maximum inflation pressure

The maximum pressure that a tyre can be inflated to.

P

Pounds per square inch (psi)

The imperial unit for air pressure.

R

Rim

The outer part of the wheel on which the tyre is mounted.

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.

Run flats

Run flat tyres enable vehicles to be driven at reduced speeds for a limited time until they can be replaced.

S

Section height

The measurement of the tyre from side to side.

Section width

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

Indicates the range of speeds at which a tyre can carry a load under a range of conditions. Ratings are categorised from A-Z.

T

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 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 driver’s door.

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 as to when 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 tyre's width that is covered by a tread pattern.

U

Under inflation

The condition that exists when there is not sufficient air pressure in a tyre.