>>488946Mountain bikes have had multiple sizes over a short time due to manufacturers marketing some new technology to make up for their lack of ability.
The first MTBs used 26" wheels. This is an American wheel size found on Schwinn cruisers that early mountain cyclists used. It's not actually 26 inches.
Then came the "29er." The rim is just a 700C (typically a road size rim) with larger tires.
650B or 27.5" is another new thing manufacturers are putting out. It's larger than 26" but smaller than a 29er.
700C, 650B, 650C and other sizes derive from old French tire sizing. The actual size can be found on the tire in parentheses. 700C is 622 mm, 650B is 584 mm, and 26'' is 559 mm.
