There are certain standards for marking bicycle tires. The exceptions are the UK and France, which use their own systems. The marking gives information about the width and inner diameter of the tire, sometimes about the height.
Diversity and Mutual Inconsistency of Bicycle Tire Labeling Systems
The generally accepted classification of bicycle tires has been developed by the International Organization for Standardization. It is known by the acronym ETRO - European Technical Organization for Rims and Caps. Only in Britain and France this system was not adopted. The marking indicates the width of the bike tire and its inner diameter in mm. You need to know this in order to select the rim size. Parameters are often indicated in inches, but such markings are not accurate enough. You can consider the types of marking in more detail.
Understanding the labeling of bicycle tires is complicated by the fact that the same tire size may be labeled differently in different countries. Therefore, often the same encoding does not mean the same size. The confusion began in the middle of the 20th century. Then, at times, tires were marked in the same way, suitable for the same rim. As a result, a 25mm wide tire fit on a size 26 rim, while the actual outer diameter of the wheel was 24 7/8 ''. Also in the 70s, there was a deliberate dishonesty of the manufacturer in specifying the parameters of the tire in order to gain an advantage in the competition.
Traditional markings and European standard
Marking with two numbers is considered traditional. The first of them means the value of the outer diameter of the tire. For example, 26 '' or 700 mm, depending on the numbering system. The second number indicates the width of the tire. In France, a letter code is used for this, where A is the narrowest tire, D is the widest. Thus, the marking on the bicycle tire looks like this: 26 × 1.75, 27 × 1 1/4, 650B. You can see that the width can be indicated by either a decimal or a simple fraction. It should be clarified that these are not interchangeable designations, despite the mathematical equality. These are tires of different sizes.
In contrast to the traditional system, the generally accepted ETRO standard recognizes the indication of bicycle tire parameters only in mm. The result is a three-digit number. You can bring the correspondence between ETRO and the traditional system with simple fractions: 622 = 28x1 ¾, 635 = 28x1 ½, 622 = 28x1 ½, 630 = 27x …, 622 = 27 × 1 ¼, 571 = 26 × 1, 597 = 26 × 1 ¼, 590 = 26 × 1, 584 = 26 × 1 ½, 571 = 26 × 1 ¾, 520 = 24 × 1, 547 = 24 × 1 ¼, 533 = 24 × 1 ½, 540 = 24 × 1 3/8, 445 = 20 × 1 ¼, 406 = 20 × 1 ¾, 419 = 20 × 1 ¾, 205 = 12 ½ × 2 ¼. Compliance with ETRO standard and traditional decimal system: 559 = 26 × 1.00 to 2.3, 599 = 26 × 1.375, 507 = 24 × 1.5 to 24 × 2.125, 406 = 20 × 1.5 - 20 × 2.125.
