How to Read Bicycle Tire Sizes

How to Read Bicycle Tire Sizes
Reading bicycle tire sizes correctly is important when you're seeking to replace your tube or tire. While it's not as important to understand what the measurements mean, it is important to be able to match the size of your tire with the size of the tube you're purchasing.


Difficulty: Easy

Step 1
Refer to your tire sidewall. Look for the tire size designation, which will feature a large and a small number designated in a formula such as "large x small."
Step 2
Read the first number, which indicates the tire diameter. Note that this number is not usually a precise measurement, so you would not get the same figure if you measured the diameter of the tire. The measurement is also your wheel size. On a mountain bike, the measurement will be indicated in inches and most likely will be 26. Some mountain bikes also use 24- or 29-inch wheels. BMX bikes use 20-inch wheels, and children's bikes also use smaller wheels. For a road bicycle, the number is indicated in millimeters and is most often 700. Some road bikes also use a 650 mm rim.
Step 3
Read the second number, which denotes the tire width. Mountain bike diameter size should fall between 1.8 and 3 inches. Road bikes most often have a width of 23 mm but also may be in sizes from 18 to 28 mm.
Step 4
Note that both wheels may not be the same size. Mountain bikes, in particular, may use different sized wheels in front and in back, so the measurements won't be identical. However, usually you would realize this when purchasing the bike because a small minority of bikes use different sized wheels.

Tips & Warnings

If your bicycle tire size is indicated as a fraction rather than as a decimal, be sure to purchase a tube that uses a fraction as well. Even if the decimal is mathematically equal to the fraction, it may not properly fit.
Don't attempt to measure your tires if you can't find the printed size because the measurements are not exact matches to the standard tire sizes. Take your bike to a shop and seek professional help in fitting your equipment.

Article Written By Joe Fletcher

Joe Fletcher has been a writer since 2002, starting his career in politics and legislation. He has written travel and outdoor recreation articles for a variety of print and online publications, including "Rocky Mountain Magazine" and "Bomb Snow." He received a Bachelor of Arts in political science from Rutgers College.

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