ISO 5775

ISO 5775 is an international standard for labeling the size of bicycle tires and rims. The system used was originally developed by the European Tyre and Rim Technical Organisation (ETRTO), and is now managed by the ISO. It is designed to make tire sizing consistent and clear, through replacing overlapping informal systems that ambiguously distinguished between sizes. For example, at least 6 different "26 inch" sizes exist (just by American notation), and "27 inch" wheels have a larger diameter than American "28 inch" (French "700C") wheels. This standard uses the bead seat diameter (BSD) as a measurement for rim and tyre widths and diameters. The Japanese Industrial Standards Committee also cooperates with ISO 5775. The corresponding Japanese standards are JIS D 9112 for tires and JIS D 9421 for rims.

Part 1, which addresses tyres' designations and dimensions, was last published in August 2023 and Part 2, addressing rims, was last published in March 2021.

Part 1 considers tyres' nomenclature, size designation, marking, dimensions and compatibility with different rims and rim widths.

Part 2 considers both general requirements and specific requirements for 5 sub types of rim: straight-sided, tubeless straight-sided, hooked bead, crochet type (not the same as hooked bead type), and tubeless crochet type rims.

Tire designations and dimensions

Part 1 considers separately the cases of clincher tyres mounted on straight sided type or crochet type rims, and hooked bead rims on which beaded edge tyres are mounted.

Clincher tyres on straight sided or crochet type rims

Clincher tires can be mounted on straight-side or crochet-type rims. Crochet-type rims are not the same as hooked-bead rims. Such tires are designated with their nominal section width and their nominal rim diameter, separated by a hyphen (-). Both are measured in millimeters. A typical example of a tire marking according to ISO 5775-1 is:

32-597 inflate to 400 kPa

The first number (nominal section width) is essentially the width of the inflated tire (minus any tread). The second number (nominal rim diameter) is the bead diameter of the tire when it is mounted on the rim, also called the bead seat diameter. The corresponding circumference can be measured with a suitably narrow tape inside the rim. The recommended inflation pressure is marked in kilopascals.

The standard notes that the minimum inflation pressure recommended is 300 kPa for narrow tires (25 mm section width or less), 200 kPa for other sizes in normal highway service, and 150 kPa for off-the-road service.

The inner width of the rim on which the tire is mounted should be about 65% of the tire's nominal section width for tires smaller than 30 mm and 55% for those larger.

The section height of a tire is usually identical to its section width (for tires less than 28 mm, 2.5 mm have to be added to the width to get the height). The overall diameter of the tire is then the rim diameter plus twice the tire's section height. The ISO 5775-1 standard also defines procedures for measuring tires and for calculating from the marking the maximum dimensions of a tire, which are needed by designers to determine clearance distances to other bicycle components.

Nominal section widths (tyres) The standard defines for each tire size a rim design width based on the tire's nominal section width, and the range of rims widths which are recommended as acceptable to be used in service for a given tire section width.

+ Rim widths for each tire size (mm) Nominal tire section width Design rim width Recommended acceptable rim width in use Min Max Min Max 18 19 15 13 15 20 21 15 13 17 22 24 17 13 20 25 27 19 13 22 28 28 19 15 23 29 34 21 16 25 35 46 23 17 27 47 57 25 17 30 58 65 30 21 35 66 71 35 25 43 72 83 45 31 53 84 95 55 41 64 96 113 76 59 89 114 132 94 72 100

Older markings

Note how in the below sorted table the "inches" measure is inconsistent with the mm measures, if height varies: Some 28-inch tires then have a measured actual bead seat diameter (BSD) smaller than a 27-inch tire. 584 mm tires are also marketed as 27.5-inch (outer diameter) tires. Older tire markings can be converted to ISO 5775 designations with the help of the following table:

+Conversion Table Actual bead diameter (mm) ISO tyre size designation Old markings (tyre outer diameter) Inches Millimetres 590 28-590 26 × × 622 28-622 28 × × 700 × 28 C 622 28 × × × 700 C Carrera 630 28-630 27 × 635 28-635 28 × 700 B 642 28-642 28 × × 700 × 28 A 239 32-239 12 × × 300 × 32 248 32-248 12 × 300 × 32 A 288 32-288 14 × × 350 × 32 298 32-298 14 × 350 × 32 A 340 32-340 16 × × 400 A 340 400 × 32 349 32-349 16 × NL 400 × 32 A 357 32-357 17 × 369 32-369 17 × 390 32-390 18 × × 450 A 390 450 × 32 400 32-400 18 × 450 × 32 A 406 32-406 20 × 438 32-438 500 × 32 ANL 440 32-440 20 × × 500 A 440 500 × 32 451 32-451 20 × 500 × 32 A 489 32-489 550 × 32 ANL 490 32-490 22 × × 550 A 490 550 × 32 501 32-501 22 × 550 × 32 A 508 32-508 22 × × 1 540 32-540 24- × 541 32-541 24 × × NL 600 A 541 600 × 32 A 547 32-547 24 × 590 32-590 26 × 650 × 32 A 597 32-597 26 × 622 32-622 28 × × 700 × 32 C 622 28 × × 700 × C Course 630 32-630 27 × 635 32-635 28 × × 700 × 28 B 635 700 B Course 288 37-288 350 A Comfort 288 350 A Balloon 298 37-298 14 × 337 37-337 16 × ANL 340 37-340 16 × NL 400 A Comfort 340 400 A Balloon 340 400 × 42 A 340 400 × 35 A 349 37-349 16 × NL 387 37-387 18 × 390 37-390 450 A Comfort 390 450 A Balloon 400 37-400 18 × 406 37-406 20 × 438 37-438 20 × NL 440 37-440 500 A Comfort 440 500 A Balloon 451 37-451 20 × 489 37-489 22 × NL 490 37-490 550 A Comfort 490 550 A Balloon 498 37-498 22 × × NL 501 37-501 22 × 540 37-540 24 × 541 37-541 600 A Comfort 541 600 A Balloon 541 600 × 35 A 565 37-565 25 × 584 37-584 27.5 × 2.0 × 2.5 584 26 × × 650 × 37 B 590 37-590 26 × 650 A 590 650 × 35 A 622 37-622 28 × × 700 × 35 C 622 28 × 642 37-642 28 × 700 × 35 A 279 40-279 14 × 350 × 38 B 288 40-288 14 × NL 350 × 38 330 40-330 16 × 400 × 38 B 406 40-406 20 × 432 40-432 20 × 440 40-440 20 × NL 500 × 38 534 40-534 24 × 540 40-540 24 × × 540 24 × × 559 40-559 24 × 1.5 571 40-571 26 × C.S. 571 26 × × NL 584 40-584 26 × 650 × 40 B 584 650 × 38 B 590 40-590 26 × × NL 622 40-622 28 × × NL 700 × 38 C 635 40-635 28 × × 700 B Standard 635 28 × 700 × 35 B 635 700 × 38 B 194 44-194 10 × 288 44-288 14 × × 350 A 288 350 × 42 A 340 44-340 16 × 428 44-428 20 × × 484 44-484 22 × × 531 44-531 24 × × 584 44-584 26 × × 650 B Semi-comfort 584 26 × × 650 B Balloon 584 26 × × 650 × 42 B 622 44-622 28 × 700 × 42 C 635 44-635 28 × × 635 28 × × 584 45-584 26 × 1.75 × 650 × 45 B 584 26 × × 203 47-203 × 1.75 × 222 47-222 11 × 305 47-305 16 × 1.75 × 2 317 47-317 16 × 355 47-355 18 × 1.75 × 2 406 47-406 20 × 1.75 × 2 406 20 × 1.75 419 47-419 20 × 457 47-457 22 × 1.75 501 47-501 T 24 × R 600 × 45 C 507 47-507 24 × 1.75 × 2 507 24 × 1.75 520 47-520 24 × 559 47-559 26 × 1.75 × 2 559 26 × 1.75 571 47-571 26 × 650 × 45 C 571 26 × 650 C S.C. 622 47-622 28 × 700 × 45 C 622 28 × 1.75 622 28 × 406 50-406 20 × 1.95 406 52-406 20 × 1.95 559 53-559 26 × 1.95 298 54-298 14 × 2 × 305 54-305 16 × 2 400 54-400 20 × 2 × 400 20 × 2 F 4 J 406 54-406 20 × 2.00 428 54-428 20 × 2 559 54-559 26 × 2.00 571 54-571 26 × × 2 571 26 × 2 × 571 26 × 2 650 × 50 C 584 54-584 26 × 2 × 584 26 × × 2 609 54-609 28 × 2 239 57-239 300 × 55 A 251 57-251 T 315 × 55 305 57-305 16 × 2.125 305 16 × 2.125 × 2 390 57-390 450 × 55 A 406 57-406 20 × 2.125 406 20 × 2.125 × 2 507 57-507 24 × 2.125 507 24 × 2.125 × 2 559 57-559 26 × 2.125 559 26 × 2.125 × 2 203 62-203 × 320 × 57 305 62-305 16 × 2.5 203 67-203 13 × 330 × 65 381 67-381 20 ×

Such older markings can be appended to the ISO 5775 designation in parentheses.

Beaded-edge tires

Beaded-edge tires are mounted on hooked-bead rims. They are marked with an overall diameter code and a nominal section-width code, separated by a cross (×). An example for such a marking is

20×1.375

Rims

Part 2 defines designations for bicycle rims. It distinguishes between

Straight-side (SS) type rims Tubeless straight-side (TSS) type rims Crochet (C) type rims Tubeless crochet type rims Hooked-bead (HB) rims

Both crochet (C) and hooked-bead (HB) rims have inner profiles that curve inwards near the outside diameter of the rim to provide a hook that helps retain the tire bead under high pressure. On modern bikes crochet rims are most common and hooked bead rims are rare. The distinction is primarily that hooked-bead rims lack the defined bead seat of straight side and Crochet-type rims. The tire is held in position radially by the hook without a bead seat playing a role. Without a bead seat, the primary designation of the diameter in terms of the bead seat is not applicable, and the governing diameter is the OD.

Rims are designated by their nominal rim diameter and their nominal width, separated by a cross (×). Both are measured in millimeters. The rim type codes SS or HB precede the rim designation, whereas code C is appended to the nominal width. Examples:

SS 400×20, HB 422×25, 620×13C

The nominal width of a rim is the inner width between the straight sides or beads as one can easily measure it with a caliper (see the standard for drawings and exact measurement procedures).

The standard widths of straight-side rims are:

18, 20, 22, 24, 27, 30.5

The standard widths of crochet-type rims are:

13C, 15C, 16C, 17C, 19C, 21C, 23C, 25C

The standard widths of hooked-bead rims are:

20, 25, 27

The diameters of straight-side and crochet-type rims are measured as the bead seat diameter (BSD). Standard values are:

194, 203, 222, 239, 248, 251, 279, 288, 298, 305, 317, 330, 337, 340, 349, 355, 357, 369, 381, 387, 390, 400, 406, 419, 428, 432, 438, 440, 451, 457, 484, 489, 490, 498, 501, 507, 520, 531, 534, 540, 541, 547, 559, 565, 571, 584, 590, 597, 609, 622, 630, 635, 642

The diameters of hooked-bead rims are measured as the outside diameter of the rim (not the tire). Standard values are:

270, 321, 372, 422, 459, 473, 510, 524, 560, 575, 611

ISO 5775

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