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Tyre Terminology


Air Pressure
Is the force exerted by air within a tyre. This is measured in Pounds per Square Inch (PSI) or KiloPascals (kPa).
Aspect Ratio
A measured term for the relationship between the height of the sidewall and the width of the tread area or cross section width of the tyre.
This is the part of the tyre that is shaped to lock into the edge of the rim upon inflation.
Bead Breaker
A tool to remove the bead from the rim in order to remove the tyre.
Black Top
Bitumen road.
Blocks – Tread
The rubber section of tread – usually large on an M/T.
Blow Out
Sudden tyre deflation
In relation to front wheel alignment and steering geometry where the tyres are tilting forward or rearward of the axle pivot.
This is the twisted fibre or filament of polyester rayon, nylon or steel which gives the tyre carcass and belts its strength.
Cord Plug
Referred to as a rope or wick type repair compound for the repair of castings.
Front wheel alignment.
Inside diameter.
KiloPascal – a measurement of pressure.
Load Index
Relates to the maximum weight permitted for each tyre at a set inflation pressure.
Design of the tyre tread featuring heavy side ‘Lugs’ that cut into mud or similar.
Mushroom Plug
An internal plug for repairing tyres.
Outside diameter of the tyre when inflated and mounted on a rim.
Over Inflation
Too much air pressure in the tyre which affects the tread contact on the road.
Plug Repair
This is a repair carried out on the tyre and can be inserted through the tyre from the inside or the outside of the casing. There are laws governing repairs which should be adhered to.
This is a layer of rubber-coated cords which run on an angle of 40 degrees across the tyre carcass.
Ply Rating
A rating relative to a tyres load carrying capacity reflecting a nominal amount of plys required to achieve the maximum load.
Pounds per square inch in relation to tyre pressure.
Radial Ply
This is a tyre with cords running radially from the bead at 90 degrees to the centre of the tyre.
Rope Repair
See Plug Repair
Section Width
The measured width of the tyre at its widest part when inflated to the manufacturer’s recommendation.
Outer edges of the tread area.
This is the side section of a tyre between the bead and the tread section.
Sipes – tread
The fine cuts in the tread blocks.
Speed Rating
Is the maximum rated speed the tyre can operate at safety.
Toe In
In relation to front wheel alignment and steering geometry where the tyres are facing inwards.
Toe Out
In relation to front wheel alignment and steering geometry where the tyres are facing outwards.
Tread Depth
This is the distance between the tyre casing and the tread blocks.
Tread Design
This is the pattern section of the tread area.
Tread Wear Indicators
These are small bars moulded across the tyre carcass. Once the tread has been worn off to these it means the tyre requires replacing.
Tubeless Tyres
A tyre that can be inflated and seals on the rim via the bead and has an external valve.
Tubed Tyre
A tyre which requires a tube for inflation.
Tyre Placard
This plaque mounted on the vehicle offers the correct tyre information for that model - things like rim and tyre combinations and air pressures.
Under Inflation
A tyre with a lower amount of tyre pressures than specified which affects the tread area on the road.
This is mounted either through the rim or as part of a tube and is how the tyre is inflated.
Void – Tread
See tread depth.

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