TIRE SIZES

Understanding the Different Size Markings on Bicycle Tires: A Comprehensive Guide

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.

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What is the difference between 28 inches and 29 inches, actually?

The silliest answer to this question would be to say that the difference is exactly 1 inch. Another answer would be: There is no difference.

Both tire sizes have the same inner diameter of 622 mm and can therefore be fitted on the same rims.

In Europe, 28 inches is a traditional size for touring bicycles. In many countries it is even the most frequent tire size used. In countries outside Europe the rim diameter of 622 mm is only rarely used. Bicycle travelers who want to buy spare tires for a 28-inch touring bicycle anywhere in the world, can tell you a thing or two about it.

A few years ago 29 inch tires were introduced as a new wheel size for mountain bikes in the US. The marking was created, as the MTB tires are more voluminous and the outer diameter measures approximately 29 inches.

Both indications are, however, very imprecise. A less wide 28 inch tire, e.g. with a tire width of 23 mm, which is usual for a road bike, has in fact only an outer diameter of something more like 26 inches. In the case of a tire width of 40 mm,
it is more or less correct that the outer diameter measures 28 inches. In the case of very wide tires with 60 mm or more, the actual outer diameter measures almost 30 inches.

What are the advantages of the new wheel sizes in 27.5 and 29 inches?

The popularity of the new wheel sizes 27.5 and 29 inches in the market is certainly justified, as the advantages of larger wheels outweigh their disadvantages. Although 29-inch wheels might be less rigid, lighter, and less likely to move in a square manner, they offer faster rolling on challenging terrains and better performance in turns. The increased contact surface significantly improves tire grip, thanks to the enhanced edge contact.

However, some bicycles do not provide enough space for a 29-inch wheel, especially those with small frames or long suspension systems. This is where the new 27.5-inch wheel size comes into the picture and becomes the optimal choice.

Schwalbe continues to commit to providing all the standard MTB tires for these three wheel diameters.