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What do the various size markings on bicycle tires mean?
Nowadays, bicycle tires sizes should all fall in line with ETRTO’s (European Tire and Rim Technical Organization) tire and rim standards. Yet the older English and French tire size markings are still used. An ETRTO size marked 37-622 indicates the width of 37 mm and the tire inner diameter of 622 mm. This designation is clear and allows an unequivocal match with the corresponding rim size. Inch size designations are less accurate. A tire marked 28 x 1 5/8 x 1 3/8 indicates an approximate outer diameter of 28 inch, the tire section height of 1 5/8-inch, and the tire section width of 1 3/8-inch. Inch sizes can also follow the pattern 26 x 2.10, which, in this case indicates only tire’s outer diameter and the tire’s section width. Inch sizes are ambiguous and lack accuracy. For example, the diameters 559 mm (MTB), 571 mm (Triathlon) and 590 mm (Touring) are all designated 26 inch. Tires with diameters 622 mm and 635 mm are both designated 28-inch, yet, surprisingly, tires with a diameter of 630 mm are designated 27-inch. A French size marked 700 x 35C, indicates the approximate tire outer diameter of 700 mm and the tire section width of 35 mm. Not all tire sizes exist as French size designations, for instance MTB sizes. Size designations on the tire