WHAT DO THE VARIOUS SIZE SPECIFICATIONS ON BICYCLE TIRES MEAN?
Nowadays, bicycle tire sizes are all marked according to ETRTO (European Tire and Rim Technical Organization) standard. However, older English and French tire size dimensions are still used as well.
The ETRTO size specification 37-622 indicates the width of 37 mm and the tire inner diameter of 622 mm. This dimension is clear and allows a precise classification of the rim size.
The inch marking (e.g. 28 x 1.40) states the approximate outer diameter (28 inches) and the tire width (1.40 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.
Inch dimensions are widely used in both MTB sport and English language countries. Therefore, we will continue to use these specifications for all tires. But only in decimal form, e.g. 26 x 2.25. Experience tells us that nowadays very few users are familiar with the classical fractional inch dimensions, such as 28 x 1 5/8 x 1 3/8.
When the 29 inch MTB tire size was introduced a few years ago, it had the same inner diameter of 622 mm, known as 28 inch in Europe. The latest tire size is 27.5 inches. This tire size is favored for MTBs which are too small for the very big 29 inch wheels, in order to benefit from the advantages of bigger diameters. This is the case, for example, with bicycles having a very long suspension travel or very small frame sizes. 27.5 inch tires have an inner diameter of 584 mm and are identical with the old French size marking 650B.
French size markings (e.g. 700 x 35C) give the approximate tire outer diameter (700 mm) and width (35 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 MTB sizes.
HOW MANY TIRE SIZES ARE THERE?
The following list shows all common tire sizes. For virtually every tire size, you should be able to find a corresponding ETRTO-size in this list.
! 28 inch and 29 inch tires have the same inner diameter of 622 mm and can be fitted on the same rims.
WHAT IS ACTUALLY THE DIFFERENCE BETWEEN 28 AND 29 INCHES?
WHAT ARE THE ADVANTAGES OF THE NEW WHEEL SIZES 27.5 AND 29 INCHES?
The new sizes are well established on the market and this is for good reason. The advantages of the large wheels outweigh the disadvantages. 29 inch wheels weigh a little more, are less maneuverable and possibly less stiff, but they roll clearly faster on rough surfaces especially in the terrain. The contact surface is bigger which makes for a significantly better tire grip.