Alpha-Numeric System

The alpha-numeric system utilizes one letter and two numbers; it is used on older vehicles. The letter signifies a maximum load rating for each tire, in pounds, according to the following chart:

TIRE LOAD RATINGS (LB.)
TIRE LOAD RATINGS (LB.)

The first number designates the tire's profile, or aspect ratio. The aspect ratio is simply the tire section height (bead-to-tread) divided by the tire section width (sidewall-to-sidewall). The profile does not include decimal points or percentages. For example, a tire with a 83 profile would be 83% as tall as it is wide (tire section only).

TIRE PROFILE

Low profile tires have low aspect ratios and look wide and squatty. The second number indicates the diameter, in inches, of the wheel (or rim) on which the tire will fit. This is not the same as the wheel rim width dimension identified above. For example, a G73-14 tire is wide enough to support 1380 pounds when properly inflated. The tire section is 73% as high as it is wide (it would belong to a group of tires called 73-Series). The tire fits on a 14" diameter wheel.

Although not part of the alpha-numeric system, All-Terrain Vehicle (ATV) tire size for off-road tires is denoted by three dimensions: outside tire diameter, tire tread width, and (inside) wheel diameter. All sizes are stated in inches.


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