The Meaning of Bicycle Tires Sizes
There are three kinds of bicycle tire size marking in the market: ETRTO size marking, The inch marking and French size marking.
ETRTO Size Marking
The ETRTO size specification 38-507 indicates the tire width of 38 mm and the tire inner diameter of 507 mm. This dimension is clear and allows a precise classification of the rim size. (Note: ETRTO refers to the European Tire and Rim Technical Organization)
The Inch Marking
Inch dimensions are widely used in both MTB sport and English language countries.
The size (e.g. 24 x 1.50) states the approximate outer diameter (24 inches) and the tire width (1.50 inches). Another inch marking is 28 x 1 5/8 x 1 3/8 (approximate outer diameter x tire height x tire width); it is also common.
The French Size Marking
French size markings (e.g. 700 x 45C) give the approximate tire outer diameter (700 mm) and width (45 mm). The letter at the end indicates the inner diameter of the tire. In this case, C stands for 622 mm. French size markings are not used for all tire sizes, so, for example, it is not used for MTB sizes.
