How are tires measured?
Nowadays, bicycle tire sizes are all marked according to ETRTO (European Tire and Rim Technical Organization) standard.
Modern Inch size nomenclature is often used.
Older English and French tire size dimensions are still used as well.The** ETRTO size** for a tire is a millimeter based measurement and is the most accurate. Schwalbe always encourages the use of ETRTO measurements during tire identification.
In the above example The ETRTO size specification 37-622 indicates the width of 37 mm and the tire inner diameter (bead to bead) of 622 mm. This dimension is clear and allows a precise classification of the rim size.
The inch marking in the above example states the approximate outer diameter (28 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.
Inch sizes are not precise and lack accuracy. For example, diameters 559 mm (MTB), 571 mm (Triathlon) and 590 mm (Touring) are all classified as 26 inch. Tires with diameters 622 mm and 635 mm are both classified as 28 inch. Oddly enough, tires with an inner diameter of 630 mm are classified as 27 inch.
These classifications originate from the time of tire brakes. In those days, the exact outer diameter of the tire was defined by the brake. Depending on tire width, various standards for the inner diameter applied.
When the 29 inch MTB tire size was introduced, it had the same inner diameter of 622 mm, known as 28 inch in Europe.
French size markings (e.g. 700 x 38C) give the approximate tire outer diameter (700 mm) and width (38 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 tires narrower then 50mm in width.
Modern Inch size nomenclature is often used.
Older English and French tire size dimensions are still used as well.The** ETRTO size** for a tire is a millimeter based measurement and is the most accurate. Schwalbe always encourages the use of ETRTO measurements during tire identification.
In the above example The ETRTO size specification 37-622 indicates the width of 37 mm and the tire inner diameter (bead to bead) of 622 mm. This dimension is clear and allows a precise classification of the rim size.
The inch marking in the above example states the approximate outer diameter (28 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.
Inch sizes are not precise and lack accuracy. For example, diameters 559 mm (MTB), 571 mm (Triathlon) and 590 mm (Touring) are all classified as 26 inch. Tires with diameters 622 mm and 635 mm are both classified as 28 inch. Oddly enough, tires with an inner diameter of 630 mm are classified as 27 inch.
These classifications originate from the time of tire brakes. In those days, the exact outer diameter of the tire was defined by the brake. Depending on tire width, various standards for the inner diameter applied.
When the 29 inch MTB tire size was introduced, it had the same inner diameter of 622 mm, known as 28 inch in Europe.
French size markings (e.g. 700 x 38C) give the approximate tire outer diameter (700 mm) and width (38 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 tires narrower then 50mm in width.
Updated on: 03/11/2025
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