Defining Motorcycle Tire Sizes

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By Hayley Harrison
eHow Contributing Writer

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To a layman, motorcycle sizes can be difficult to understand as they typically are made up of a series of numbers. Fortunately, once one comes to understand how sizing of motorcycle tires works, it is much easier to select the right size tire.

Metric Designation

A motorcycle tire's size is written in a series of three numbers called a metric designation. The format of the numbers looks something like this: 1/2 3.

Width

The first number in the metric designation is the width. This measurement is taken from one edge of the tire's tread to the opposite tread's edge and is calculated in centimeters. Common width for front tires is between 110 and 150 cm and 80 cm to 130 cm for rear tires.

Aspect

The second number in the metric designation is the aspect ratio of the tire, which compares the tire's width to its height. The higher the number, the taller the motorcycle will sit from the ground. Most tires are outfitted with aspect ratios of between 40 and 90.

Diameter

The final number in the metric designation is the diameter, which simply measures the tire's rim diameter. Common diameters range from 15 cm to 18 cm.

Older tires

Older tires may features sizes that include letters and numbers called the alphanumeric system. This is an antiquated method of sizing that has been replaced by the metric designation; however, charts for reading old motorcycle sizes are available online.