Motorcycle Tire Sizes Explainedby Marijon Shearer
Two coding systems are used in the United States to size motorcycle tires. One uses numerals to express the tire size; the other uses a combination of numerals and letters. Either system, however, may add letters to the size to give other information about a tire.
Where to Look
Look on the sidewall for the tire size. Examples of tire sizes are 130/90 16 and MT90 16.
All tire sizes end with the diameter, in inches, of the rim that goes with that tire. Tires sized 130/90 16 and MT90 16 would both fit a 16-inch rim.
The tire’s height divided by its width, or “aspect ratio,” is the number preceding the rim size in both tire sizing systems. On a 130/90 16 and a MT90 16 tire, the aspect ratio is 90, meaning the height of the tire is 90 percent of its width.
An all-numeral tire size such as 130/90 16 means the tire is 130mm wide on a 16-inch rim with an aspect ratio of 90. This method is called “metric,” even though the rim size is in inches. Some tires show width in inches and without the aspect ratio—for example, 5.00—16 for a tire 5 inches wide on a 16-inch rim (with the dash showing the tire is bias-ply construction).
Numbers and Letters
In the older “alphanumeric” sizing system, a letter to the left of the aspect ratio indicates tire width. For example, on a tire sized MT90 16, the T means the tire is 130mm wide. The second letter is the one that matters—they all start with M, for “motorcycle.”
Remember, letters to the left of the aspect ratio show tire width in the alphanumeric sizing system. Letters that show up elsewhere in either tire sizing system show speed rating and construction of the tire; for example, R or B means the tire is radial or belted-bias construction, and Q, S, T, U, H, V, W, Y and Z indicate maximum speeds the tire can handle.
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