Tyre Talk What Do the Numbers Mean

Tyre Talk - What Do the Numbers Mean?

Every modern tyre has markings on the tyre wall. These markings are a series of numbers and codes, used internationally, and exist for the identification of tyre structures, dimensions and applications. The illustration (below) gives an example of the markings, as they appear on a passenger tyre:

A tyre's age can be identified from the U.S. Department of Transportation (DOT) coding located on its sidewall. The last numbers on the DOT donate the week and year of construction. The full DOT is only on one side of the tyre. In some cases, tyres will have a partial DOT on the other wall. The partial DOT will not show the tyre's age.

Service life is dependent on many variables such as driving conditions, vehicle loads, inflation pressure, and general maintenance or abuse of the tyre. There is not a specific age at which tyres have to be replaced. Much can depend on how the tyre has been exposed to the elements, stored, either on or off the vehicle and in general treated. The last thought though is if you are ever in doubt of the condition of the tyre (especially if it is showing signs of weathering) replace it.

The DOT though National Highway Traffic Safety Administration's (NHTSA) also has Uniform Tire Quality Grade Standards (UTQG)

Tyre Width
Maximum width of the tyre measured in millimetres from mid sidewall to the same point on the opposite sidewall.

Tyre Profile
Height of the tyre’s sidewalls expressed as a percentage of the maximum section width.

Wheel Size
The diameter of the wheel expressed in inches.

Load & Speed Rating
Indicates the maximum load carrying capacity of the tyre when operating at its maximum speed capability. The maximum speed capability is indicated by a letter and the maximum load carrying capacity by a number, which is represented as an index.

Brand Name

Model Type
Describes the tread pattern design.

Maximum Load
The tyre’s maximum load carrying capacity.

Maximum Pressure
The tyre’s maximum operating inflation pressure.

USA DOT Code
A US Department of Transport federal requirement to allow the tyre to be sold and operated in North America.

UTQG Standards
Uniform Tyre Quality Grading (Applicable only to the USA).

UTQG grading is required by US law for most passenger car tyres sold in the United States (not deep treaded light truck tyres). There are three grading categories: Traction / Tread wear / Heat. These are branded on the tyre's upper sidewall.

Tyre Talk - What Do the Numbers Mean?

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