ETRTO (European Tire and Rim Technical Organization): Standards organization for tire and rim sizes.

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.

NOTE: Always reference the ETRTO number when ordering to ensure accuracy in tire fit.

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.