### Decimal size

Decimal notation | ISO, mm | Application |

29 inch | 622 | An accepted name coined by marketers. Refers to tires with a rim diameter of 622 mm (“700c”). |

28 x [dec. number] | 622 | Some German tire manufacturers use this designation for tires with a rim of 622 mm (“700c”). |

26 x 1.00 to 2.3 | 559 | Most mountain bikes, cruisers, etc. Except the following: |

26 x 1.25 (obsolete) | 599 | Very old light bicycles from the USA. |

26 x 1.375 | 599 | Very old light bicycles from the USA. |

24 x 1.5-24 x 2.125 | 507 | Children’s mountain bikes, cruisers. |

22 x 1.75; 22 x 2.125 | 457 | Children’s bicycles. |

20 x 1.5-20 x 2.125 | 406 | Most BMX bikes, kids bikes, folding bikes, touring bikes and some liguerades. |

18 x 1.5 | 355 | Folding bikes Birdy. |

18 x 1.75-18 x 2.125 | 355 | Children’s bicycles. |

16 x 1.75-16 x 2.125 | 305 | Children’s bicycles, folding, touring and some liguerades. |

## False marking

In fierce competition, the accuracy of information provided by manufacturers often suffers. Suppose you are looking for high quality 700-25 tires. Naturally, you go through catalogs and advertisements to find the lightest tires in this size. If, for example, Pepsi Tire and Coke Tire make tires of the same technology and roughly the same quality, but Pepsi labels a 24mm tire as 700-25, it will weigh less than Coke’s honestly labeled 700-25. This marketing ploy gives Pepsi a tangible advantage. In response, Coke is releasing an even lighter 700-23 tire, re-labeling it as 700-25.

In the 70s and 80s, this kind of marketing ploy was very popular. As a result, the situation was completely out of control, and all manufacturers had to take their heads and begin to indicate only the true sizes of their products.

### 26″ To 700c Wheel Conversion On Mountain Bike

The International Organization for Standardization (ISO) has developed a universal tire size designation system in order to avoid errors and various incompatibility problems. This system was originally known as the “ETRTO system”, developed by the company of the same name (European Tire and Rim Technical Organization).

There are two numbers involved in the ISO system. The first indicates the width of the tire or rim in millimeters. The actual width of the tire depends on the width of the rim, which is measured along the inner beads (see picture).

The second number according to the ISO system is the most important. it denotes the rim bore diameter (BSD, from the English “Bead Seat Diameter”) in millimeters. It defines the interchangeability of tires. If this number matches the rim and tire, then they are compatible.

### 700c Vs 26 Inch *Bicycle Wheels*: Pros and Cons

For example, a 700 x 20 C road tire is ISO 20-622; hybrid tire 700 x 38. as 38-622. differences in width, perhaps they are not an ideal replacement for each other, but most importantly, any rim that a 20-622 tire fits on will also fit a 38-622 tire.

Also, it is important to consider that the width of the tire should be 1.45-2 times wider than the inner width of the rim.

If you deflate the tire and measure its width between the beads, the result will be approximately 2.5 times the value according to the ISO standard.

The following tables show the correspondence between US standard sizes and ISO bore diameters.

### ISO Correspondence Table

ISO Rim diameter, mm | Accepted designation |

635 | 28 x 1 1/2, 700 B |

630 | 27 x number |

622 | 700 C, 28 x (two fractions), 29 in. (28 x 1 1/2 F.13 Canada) |

599 | 26 x 1.25 x 1.375 |

597 | 26 x 1 1/4, 26 x 1 3/8 (S-6) |

590 | 26 x 1 3/8 (E.A.3), 650 A |

587 | 700 D |

584 | 650B, 26 x 1 1/2 |

571 | 26 x 1, 26 x 1 3/4, 650 C |

559 | 26 x 1.00- x 2.125 |

547 | 24 x 1 1/4, 24 x 1 3/8 (S-5) |

540 | 24 x 1 1/8, 24 x 1 3/8 (E.5), 600 A |

520 | 24 x 1, 24 x 1 1/8 |

507 | 24 x 1.5- x 2.125 |

490 | 550 A |

457 | 22 x 1.75; x 2.125 |

451 | 20 x 1 1/8; x 1 1/4; x 1 3/8 |

440 | 500 A |

419 | 20 x 1 3/4 |

406 | 20 x 1.5- x 2.125 |

390 | 450 A |

369 | 17 x 1 1/4 |

355 | 18 x 1.5- x 2.125 |

349 | 16 x 1 3/8 |

340 | 400 A |

337 | 16 x 1 3/8 |

317 | 16 x 1 3/4 |

305 | 16 x 1.75- x 2.125 |

203 | 12 1/2 x number |

152 | 10 x 2 |

137 | 8 x 1 1/4 |

### Fractional size

Fractional designation | ISO, mm | Application |

29 inch | 622 | An accepted name coined by marketers. Refers to tires with a rim diameter of 622 mm (“700c”). |

28 x 1 1/2 | 635 | English, Danish, Chinese and Indian road bikes with rod brakes (also designated F10, F25, 700 B). |

28 x 1 5/8 x 1 1/4 | 622 | Obsolete Canadian designation F.13. |

28 x 1 5/8 x 1 1/4 | 622 | North European designation for tires with a rim of 622 mm (700 C). |

27 x [number] | 630 | Old road bikes. |

26 x 1 (650 C) | 571 | Triathlon, time trial, small road bikes. |

26 x 1 1/4 | 597 | Old British sports and club bikes. |

26 x 1 3/8 (S-6) | 597 | Light bikes from Schwinn. |

26 x 1 3/8 (E.A.3) | 590 | Most 3-speed bikes, 10-speed kids’ bikes or supermarket bikes. |

26 x 1 1/2 (650B) | 584 | French walking or touring bikes, a few Raleigh (US) and Schwinn mountain bikes. |

26 x 1 3/4 (S-7) | 571 | Schwinn cruisers. |

24 x 1 | 520 | High quality wheels for short riders. |

24 x 1 1/8 | 520 or 540 | Buyer Be Vigilant! |

24 x 1 1/4 | 547 | Children’s bicycles Schwinn or British. |

24 x 1 3/8 (S-5) | 547 | Schwinn children’s light bikes. |

24 x 1 3/8 (E-5) | 540 | British kids bicycles, most wheelchairs. |

20 x 1 1/8 20 x 1 1/4 20 x 1 3/8 | 451 | Light bikes for kids, BMX for light riders, some liguerades. |

20 x 1 3/4 | 419 | Schwinn children’s bicycles. |

17 x 1 1/4 | 369 | Alex moulton. |

16 x 1 3/8 | 349 | Old Moulton, Brompton and other folding bikes, Liguerad front wheels, kids bikes. |

16 x 1 3/8 | 337 | Extremely mysterious tire size. |

16 x 1 3/8 | 335 | Polish children’s bicycles. |

16 x 1 3/4 | 317 | Schwinn children’s bicycles. |

12 1/2 x [number] | 203 | Children’s bicycles, scooters |

10 x 2 | 152 | Wheelchairs. |

8 x 1 1/4 | 137 | Wheelchairs. |

It is also worth noting that fractional dimensions were originally introduced for old rims with straight sidewalls. functional dimensions 571 mm / 26 x 1 and 630 mm / 27 appeared later on rims with ribs.

## Width calculation

Of course, you can use almost any combination of tire and rim that has the same fit, but from a practical point of view, it is unwise for the tire width to be significantly different from the rim width.

If the tire is too wide, the likelihood of rapid wear of the sidewalls of the tire increases, as well as the risk of losing control of the bike on a flat tire. Plus, the handling at low speeds noticeably worsens.

Unfortunately, in order to save weight, modern mountain bikes use extremely narrow rims. Wide tires are very poorly suited to such rims, unless they are very inflated. This, in turn, leads to unnecessary stress on the sidewalls of the rim, and in addition, the main point of installing wide tires designed to work with low pressure is lost.

## Bicycle tire size

## Standard notation system

The standard designation system is based on the measurement of the outer diameter of the tire. This size is usually expressed in either inches (26 “, 27”, etc.) or millimeters (650, 700, etc.).

Unfortunately, the evolution of rims and tires has led to the fact that these markings no longer match the actual diameter. The history of this confusion dates back to the 30s of the last century, when heavy, thick tires “baluners” measuring 26 x 2.125 were popular, which are still installed on some walking and beach bicycles. The outer diameter of such a wheel is very close to 26 “. Many cyclists, however, were not completely satisfied with the characteristics of these wheels and wanted a faster and lighter one. The industry responded to their request by producing lighter and narrower tires that fit the same rim, and designated 26 x 1.75.

Although these tires continued to be called “26-*inch*” tires, their actual diameter was 25 5/8 “, not 26”. Later, the pioneers of the mountain bike from the west coast of the United States used the same rim size, which remains the standard for it today. The market began to dictate its terms to manufacturers, and tires with a width of only 25 millimeters for the “26-inch” rim appeared on sale. In reality, the outer diameter of the wheel was 24 7/8 “.

In the standard designation of the tire size, the second number or letter code indicates its width. For example, 26 x 1.75; 27 x 1 1/4; 650B; 700C.

## GMS and WTB

GMS. Global Measuring System. The existing standards for measuring the size of an inflated tire do not take into account the difference in tread depth. To solve this problem and make it possible to compare the characteristics of tires more accurately, WTB introduced its measurement standard. GMS.

The standard consists of two numbers in millimeters: the first characterizes the width of the base of the tire; the second is the width of the outer portion of the tire, measured over the tread. Measured on a 20mm inner width rim and tire inflated to 60 psi and after 24 hours of soak.

In addition to the dimensions of the base and the outer tread width, the admissible tire pressure, the main characteristics of the tread and its contact zone are indicated.