Bike Tire Sizes Explained

International organization for standardization.

Bike tire sizes explained.

Road bike tires generally come in three widths. Conversion tables for common bicycle tire sizes. After the speed rating there will be a b or r to indicate if it is belted or radial tire construction. If there is no speed rating the m will precede the metric size.

Bike tube sizing essentially mirrors bike tire sizing with one exception. Metric tires are most commonly used and can work for sport bikes cruisers touring bikes and others. 27 5 x 1 9 2 3 for example. To make matters worse in the early days of cycling every country that manufactured bicycles developed its own system of marking the sizes.

Nowadays bike tires are typically marked according to iso standard a system originally developed by etrto european tire and rim technical organization but older english and french tire size dimensions are still used as well use the data from the following tables to determine interchangeability and convert between iso etrto english. The letter at the end of a tire size is a throwback to an old french system when the letters a b and c designated different inner tire diameters it does not stand for cm. When it comes to choosing width there are two major factors at play. Bicycle tires come in a bewildering variety of sizes.

Tubes because they can stretch will list a range of widths. Thus you need to be sure any new bike tube has sizing that has a width range that aligns with the sizing on your bike tires. The same size tire would be known by different numbers in different countries. Because of the high pressure and desired low rolling resistance road tires come in narrow widths.

Common road bike widths in millimeters come in sizes ranging from 18 to 23 with a typical road bike tire at 700 x 23. Some older road bikes still have the 27 inch size.