Common Tyre Terms

Below are some popular tyre terms with their definitions and descriptions.

Radial Tyres
Body cords run across the tyre perpendicularly to the beads. Radial tyres have belt plies, which run nearly circumferentially around the tire, under the tread to stabilize the tread, strengthen the tread area and add flexibility to the sidewall. By restricting tread movement during contact with the road, the belt plies improve tread life.

Bias Ply (Diagonal) Tires 
Have two, four, or more body plies, which cross at an angle to the centerline of the tread, to strengthen both the sidewall and the tread.

Belted Bias Tires 
Have a body similar to that of bias tires, plus two or more belts under the tread to strengthen and stabilize the tread. The belts improve tread life by reducing tread movement during contact with the road.

Air pressure 
Forces exerted by air within tire, expressed in pounds per square inch.

Aspect Ratio 
A numerical term that expresses the relationship between the standing height of the tire and the cross section width. (Aspect Ratio of 70 means the tire section stands approximately 70 percent as high as it is wide between the sidewall).

That part of the tire that is shaped to fit the rim. Made of high tensile steel wires that are wrapped in woven fabric and then held by the plies.

Carrying Capacity 
Maximum rated tire load for a given inflation pressure as established by the Tire and Rim Association.

Load Carrying Capacity 
Maximum load for which tire is designed under standard conditions.

Load Range 
A system of designations that identify the carrying capacity range of a tire. These markings shown on the tire indicate the ply rating established for the tire. Passenger tire designations are B (4-ply rating), C (6-ply rating), and D (8-ply rating). This system was established by the Rubber Manufacturers Association and is used on all American-made Tires. Replaces ply rating.

Speed Rating 
A speed Designation of S, T, H, V, or Z shown in the size marking of some tires.

Ability of tires to maintain direction of vehicle on curve without causing excessive sway.

Tread Depth 
The distance in thirty – seconds of an inch measured from the tread surface to the bottom of the grooves in a tire.

Tread Design 
The pattern of the tread area.

Tread Wear Indicators 
Narrow bars of rubber molded at a height of 2/32″ across the bottom of the tread grooves. When the tread wears down to these bars, the tire should be replaced.

Under inflation 
Tire having less than recommended air pressure for the load being carried.