How Are Bike Sizes Measured?

Different Bicycle Sizes?

Bicycle frame sizes and tire sizes differ, but neither of these apply when talking about whether a bicycle is 16 inches, 24 inches, 26 inches, 27 inches or 700 millimetres. These designations can be confusing, but one wonders how a manufacturer determines what to call a push bike's rim size.

The Inches Refer to Rim Size

A bicycle size refers to the diameter of the tire's rim. Bicycles sizes are commonly given in inches. Newer street bikes will be referred to as 700 millimetres, however. 26-inch bicycles, for example, are not always the same size. Often this variation is due to differences between bicycle manufacturers.

Tire Sizes and Bicycle Rim Measurement

Street bikes tend to have narrower tires and smaller inner tubes. A 26-inch bike that requires a 26 x 1.75 tire will not necessarily fit a rim whose tire requires 26 x 1 3/4 tire size. The rims are not always the same size, despite the two phrases being mathematically equivalent, according to the Sheldon Brown cycling web site. The size difference may be by a fraction of an inch, but when a bicycle owner must buy new tires, he must make sure the number designations match up exactly to the old tire.

27-Inch Bicycle Rims Versus 700 Milimeter Rims

Older bicycles came with a rim size of 27 inches, but bicycles with this rim size are no longer made. The 700 millimetre street and racing bikes are of similar size to the older 27-inch rim bicycles, but the two tire sizes are not interchangeable. People with 27-inch bicycles will most likely have to visit a specialty shop to find tires for their bicycles.