Explanation of Bicycle Tire Sizes

Explanation of Bicycle Tire Sizes
When it's time to buy a new set of bike tires, it's important to purchase a set that will fit the rim of your wheel. Take time to learn about how bike tire sizes wok and you will be able to shop for your next pair with confidence.


The diameter of your tire is written on your tire's sidewall. It's the first number in the number set that's separate with an X. For example, a 26x2.1 tire has an diameter of roughly 26 inches.



The width of the tire is the second number in the number set. For example, a 700X23 tire has a width of 23MM.

Inches and Millimeters

Adult bike tires are measured using either inches or millimeters. The standard size tire for a mountain bike is 26 inches and the standard for a road bike is 700MM.

Fractions and Decimals

The width of a tire may be written as either a fraction or a decimal. Unfortunately, a 1 1/4" width is not the same size as a 1.25 width, even though they have the same numeric value.

Not True to Measurement

If you measure the width of your 25MM tire, you may find that it is actually 24MM. Companies have been able to cheat by marking a 24MM tire as a 25MM tire, thereby making their "25MM" tire lighter than their competitors.


The diameter of your new tire must match the diameter of your wheel. Every wheel can accommodate a range of tire widths. See the Resource section for a compatibility chart.


Article Written By Kathrine Cole

Kathrine Cole is a professional outdoor educator. She teaches rock climbing, backpacking, cycling, and bike maintenance classes. She is a graduate of the National Outdoor Leadership School, a Wilderness First Responder, and a Leave No Trace Trainer.

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