## The diversity and mutual inconsistency of marking systems sunglasses

The standard classification of Bicycle tires was developed by the International organization of standardization. She is known by the acronym ETRO - European technical organization rims and caps. Only in Britain and France this system is not adopted. In the marking are given width women's shoes and its inner diameter in mm. It is necessary to know to select the size of the rim. Often the parameters are specified in inches, but such marking is not precise enough. You can consider the marks in detail.

Understanding labeling bike tires is complicated by the fact that one and the same size tire can be in different countries are marked in different ways. So often the same encoding does not mean identical size. The confusion began in the mid-twentieth century at times equally marked tyre suitable on the same rim. As a result, the rim 26 size fit tyre width of 25mm, and the actual outer diameter of the wheel was equal to 24 7/8’. Also in the 70s was marked, deliberate dishonesty of the manufacturer to specify the parameters of the tyre, to gain advantage in the competition.

## Traditional marking and European standard

Traditional is the marking of the two numbers. The first one is the value of the outside diameter of the tire. For example, a 26’ or 700 mm, depending on the accounting system. The second number is the width of the tyre. In France, this use of the letter code, where A is the most narrow tire, D is the widest. Thus, the marking on velasina looks so: 26×1.75, 27×1 1/4, 650B. You can see that the width can be indicated as a decimal or simple fraction. It is necessary to clarify that it is not interchangeable notation despite the mathematical equality. It tires of different sizes.

Unlike traditional systems, a common standard ETRO acknowledges specifying parameters only bike. the result is a three-digit number. Can result according ETRO and traditional systems with simple fractions: 622 = 28x1¾, 635 = 28x1½, 622 = 28x1½, 630 = 27x..., 622 = 27×1 ¼ , 571 = 26×1, 597 = 26×1 ¼, 590 = 26× ¼ 1, 584 = 26×1½", 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 = 20×1¾, 419 = 20×1¾, 205 = 12 ½ ×2¼. Complying with ETRO, and a traditional system with decimal fractions: 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.