The most common bikes wheel sizes are the 26 and 24 inch types. The 26 inch wheel is very popular in the United States. It has a 559 mm rim. More often than not, the edges are hooked. However, there are many other sizes available.
While there are many kinds of rims and tires, there are efforts to develop standards. This has become necessary for compatibility reasons. In the US, measurements are in inches. In Europe, the standards are set by the European Tyre and Rim Technical Organisation (ETRTO) and International Organization for Standardization (ISO).
If the tires are wired-edge, the diameter and width (when the tire is inflated) are listed. The bikes wheel sizes are set in mm with a hyphen separating them. If the tire shows 37-622, it is 37 mm wide and 622 mm in diameter.
With rims, their inner width and rim diameter are specified. The diameter refers to where the tire sits. A cross separates the two. The figure is expressed in millimeters. The rim type is specified by a letter. The majority of tires also have other information on them. There are variations in some of the designations.
The majority of racing and road bicycles employ the 622 mm diameter (700C) rims. For triathletes and small riders, 650C rims are more popular. The 650C models have a diameter of 571 mm. The 650A has a diameter of 590 mm and the 650B a diameter of 584 mm. Mountain bikes for adults rely on the 26” wheels. Mountain bikes for younger people use the 24 inch wheels.
Bikers for big riders use 700C 29 inch wheels. These are for heavy duty use. The 27 inch wheel used to be popular but has fallen out of favor. The rims are a tad bigger than the 700C diameter wise. These 27 inch wheels cannot be used with tires and frames made for the 700C.
Wheels for children’s bikes are primarily set by the diameter of the wheel. For this reason, the dimensions vary a great deal. The range is from 12 inches to 18 inches. A few are bigger.
Besides bikes wheel sizes, the rims differ also. The widths differ due to optimization reasons. The racing rims for high performance road racing are 18 mm or less. Durable off-road tires and those on touring bikes are wider at 24 mm. There may be other variants out there, but these are the most common.