Many of the bicycle tires and rims used all over the world are based on older British inch-based standards. However, their dimensions are defined and labelled today in millimetres according to the international standard format defined in ISO 5775.
For example, a normal "wired edge" tire (for straight-side and crotchet-type rims) with a "nominal section width" of 32 mm, a "nominal rim diameter" of 597 mm, and a "recommended inflation pressure" of 400 kPa is marked according to ISO 5775-1 as:
32-597 inflate to 400 kPa
The first number (nominal section width) is essentially the width of the inflated tire (minus any tread) in millimetres. 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 second number (nominal rim diameter) is essentially the inner diameter of the tire in millimetres when it is mounted on the rim. The corresponding circumference can be measured with a suitably narrow tape inside the rim.
The minimum inflation pressure recommended for a "wired edge" tire 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 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. ISO 5775-1 also defines how to measure tires and how to calculate the maximum dimensions of a tire (as needed for clearances) from its designation.
For "wired edge" tires, the standard defines a set of nominal section widths and provides this list of recommended rim widths for each:
Nominal section Recommended rim widths width of tire Straight-side rim Crotchet-type rim 16 - 13C 18 - 13C 20 - 13C 23 16 13C, 15C 25 16, 18 13C, 15C, 17C 28 16, 18, 20 15C, 17C, 19C 32 16, 18, 20 15C, 17C, 19C 35 18, 20, 22 17C, 19C, 21C 37 18, 20, 22 17C, 19C, 21C 40 20, 22, 24 19C, 21C, 23C 44 20, 22, 24, 27 19C, 21C, 23C, 25C 47 20, 22, 24, 27 19C, 21C, 23C, 25C 50 22, 24, 27, 30.5 21C, 23C, 25C 54 27, 30.5 25C 57 27, 30.5 25C 62 27, 30.5 -
For "wired edge" tires, ISO 5775-1 provides a comprehensive conversion table between older markings and the modern ISO size designations:
Tire size | designation | Old marking (inch or using outer diameter in mm) -------------|----------------------------------------------------- 28-590 | 26 × 1 3/8 × 1 1/8 -------------|----------------------------------------------------- 28-622 | 28 × 1 5/8 × 1 1/8 700 × 28C | 28 × 1 5/8 × 1 1/4 × 1 1/8 700 C Carrera -------------|----------------------------------------------------- 28-630 | 27 × 1 1/4 fifty -------------|----------------------------------------------------- 28-635 | 700 B -------------|----------------------------------------------------- 28-642 | 28 × 1 3/8 × 1 1/8 700 × 28 A -------------|----------------------------------------------------- 32-239 | 12 × 1 3/8 × 1 1/4 300 × 32 -------------|----------------------------------------------------- 32-248 | 12 × 1 1/4 300 × 32 A -------------|----------------------------------------------------- 32-288 | 14 × 1 3/8 × 1 1/4 350 × 32 -------------|----------------------------------------------------- 32-298 | 14 × 1 1/4 350 × 32 A -------------|----------------------------------------------------- 32-340 | 16 × 1 3/8 × 1 1/4 400 A | 400 × 32 -------------|----------------------------------------------------- 32-349 | 16 × 1 1/4 NL 400 × 32 A -------------|----------------------------------------------------- 32-357 | 17 × 1 1/4 -------------|----------------------------------------------------- 32-369 | 16 × 1 1/4 -------------|----------------------------------------------------- 32-390 | 18 × 1 3/8 × 1 1/4 450 A | 450 × 32 -------------|----------------------------------------------------- 32-400 | 18 × 1 1/4 450 × 32A -------------|----------------------------------------------------- 32-438 | 500 × 32 ANL -------------|----------------------------------------------------- 32-440 | 20 × 1 3/8 × 1 1/4 500 A | 500 × 32 -------------|----------------------------------------------------- 32-451 | 20 × 1 1/4 500 × 32 A -------------|----------------------------------------------------- 32-489 | 550 × 32 ANL -------------|----------------------------------------------------- 32-490 | 22 × 1 3/8 × 1 1/4 550 A | 550 × 32 -------------|----------------------------------------------------- 32-501 | 22 × 1 1/4 550 × 32 A -------------|----------------------------------------------------- 32-508 | 22 × 1 1/4 × 1 -------------|----------------------------------------------------- 32-540 | 24-1 3/8 × 1 1/4 -------------|----------------------------------------------------- 32-541 | 24 × 1 3/8 × 1 1/4 NL 600 A | 600 × 32 A -------------|----------------------------------------------------- 32-547 | 24 × 1 1/4 -------------|----------------------------------------------------- 32-590 | 26 × 1 3/8 1 1/4 650 × 32A -------------|----------------------------------------------------- 32-597 | 26 × 1 1/4 -------------|----------------------------------------------------- 32-622 | 28 × 1 5/8 × 1 1/4 700 × 32C | 28 × 1 1/4 × 1 3/4 700 × C Course -------------|----------------------------------------------------- 32-630 | 27 × 1 1/4 -------------|----------------------------------------------------- 32-635 | 28 × 1 1/2 × 1 1/8 700 × 28 B | 700 B Course -------------|----------------------------------------------------- 37-288 | 350 A Comfort | 350 A 1/2 Balloon -------------|----------------------------------------------------- 37-298 | 14 × 1 3/8 -------------|----------------------------------------------------- 37-337 | 16 × 1 3/8 ANL -------------|----------------------------------------------------- 37-340 | 16 × 1 3/8 NL 400 A Comfort | 400 A 1/2 Balloon | 400 × 42 A | 400 × 35 A -------------|----------------------------------------------------- 37-349 | 16 × 1 3/8 NL -------------|----------------------------------------------------- 37-387 | 18 × 1 3/8 -------------|----------------------------------------------------- 37-390 | 450 A Comfort | 450 A 1/2 Balloon -------------|----------------------------------------------------- 37-400 | 18 × 1 3/8 -------------|----------------------------------------------------- 37-438 | 20 × 1 3/8NL -------------|----------------------------------------------------- 37-440 | 500 A Comfort | 500 A 1/2 Balloon -------------|----------------------------------------------------- 37-451 | 20 × 1 3/8 -------------|----------------------------------------------------- 37-489 | 22 × 1 3/8 NL -------------|----------------------------------------------------- 37-490 | 550 A Comfort | 550 A 1/2 Balloon -------------|----------------------------------------------------- 37-498 | 22 × 1 3/8 × 1 1/4 NL -------------|----------------------------------------------------- 37-501 | 22 × 1 3/8 -------------|----------------------------------------------------- 37-540 | 24 × 1 3/8 -------------|----------------------------------------------------- 37-541 | 600 A Comfort | 600 A 1/2 Balloon | 600 × 35 A -------------|----------------------------------------------------- 37-565 | 25 × 1 3/8 -------------|----------------------------------------------------- 37-584 | 26 × 1 1/2 × 1 3/8 | 26 × 1 3/8 × 1 1/2 -------------|----------------------------------------------------- 37-590 | 26 × 1 3/8 650 A | 650 × 35 A -------------|----------------------------------------------------- 37-622 | 28 × 1 5/8 × 1 3/8 700 × 35 C | 28 × 1 3/8 1 5/8 -------------|----------------------------------------------------- 37-642 | 28 × 1 3/8 700 × 35 A -------------|----------------------------------------------------- 40-279 | 14 × 1 1/2 350 × 38 B -------------|----------------------------------------------------- 40-288 | 14 × 1 1/2 NL 350 × 38 -------------|----------------------------------------------------- 40-330 | 16 × 1 1/2 400 × 38 B -------------|----------------------------------------------------- 40-432 | 20 × 1 1/2 -------------|----------------------------------------------------- 40-440 | 20 × 1 1/2 NL 500 × 38 -------------|----------------------------------------------------- 40-534 | 24 × 1 1/2 -------------|----------------------------------------------------- 40-540 | 24 × 1 3/8 × 1 1/2 | 24 × 1 1/2 × 1 3/8 -------------|----------------------------------------------------- 40-571 | 26 × 1 1/2 C.S. | 26 × 1 5/8 × 1 1/2NL -------------|----------------------------------------------------- 40-584 | 26 × 1 1/2 650 × 35 B | 650 × 38 B -------------|----------------------------------------------------- 40-590 | 26 × 1 3/8 × 1 1/2 NL -------------|----------------------------------------------------- 40-622 | 28 × 1 5/8 × 1 1/2 NL 700 × 38 C -------------|----------------------------------------------------- 40-635 | 28 × 1 1/2 × 1 3/8 700 B Standard | 28 × 1 1/2 700 × 35 B | 700 × 38 B -------------|----------------------------------------------------- 44-194 | 10 × 1 5/8 -------------|----------------------------------------------------- 44-288 | 14 × 1 3/8 × 1 5/8 350 A | 350 × 42A -------------|----------------------------------------------------- 44-340 | 16 × 1 5/8 -------------|----------------------------------------------------- 44-428 | 20 × 1 5/8 × 1 1/2 -------------|----------------------------------------------------- 44-484 | 22 × 1 5/8 × 1 1/2 -------------|----------------------------------------------------- 44-531 | 24 × 1 5/8 × 1 1/2 -------------|----------------------------------------------------- 44-584 | 26 × 1 1/2 × 1 5/8 650 B Semi-comfort | 26 × 1 5/8 × 1 1/2 650 B 1/2 Balloon | 26 × 1 3/4 × 1 1/2 650 × 42B -------------|----------------------------------------------------- 44-622 | 28 × 1 5/8 700 × 42 C -------------|----------------------------------------------------- 44-635 | 28 × 1 5/8 × 1 1/2 | 28 × 1 1/2 × 1 5/8 -------------|----------------------------------------------------- 47-203 | 12 1/2 × 1.75 × 2 1/4 -------------|----------------------------------------------------- 47-222 | 11 × 1 3/4 -------------|----------------------------------------------------- 47-305 | 16 × 1.75 × 2 -------------|----------------------------------------------------- 47-317 | 16 × 1 3/4 -------------|----------------------------------------------------- 47-355 | 18 × 1.75 × 2 -------------|----------------------------------------------------- 47-406 | 20 × 1.75 × 2 | 20 × 1.75 -------------|----------------------------------------------------- 47-419 | 20 × 1 3/4 -------------|----------------------------------------------------- 47-501 T | 24 × 1 3/4 R 600 × 45 C -------------|----------------------------------------------------- 47-507 | 24 × 1.75 × 2 | 24 × 1.75 -------------|----------------------------------------------------- 47-520 | 24 × 1 3/4 -------------|----------------------------------------------------- 47-559 | 26 × 1.75 × 2 | 26 × 1.75 -------------|----------------------------------------------------- 47-571 | 26 × 1 3/4 650 × 45 C | 26 × 1 5/8 650 C S.C. -------------|----------------------------------------------------- 45-584 | 26 × 1.75 × 1 1/2 650 × 45 B | 26 × 1 1/2 × 1 3/4 -------------|----------------------------------------------------- 47-622 | 28 × 1 3/4 700 × 45 C | 28 × 1.75 | 28 × 15/8 1 3/4 -------------|----------------------------------------------------- 54-298 | 14 × 2 × 1 3/4 -------------|----------------------------------------------------- 54-305 | 16 × 2 -------------|----------------------------------------------------- 54-400 | 20 × 2 × 1 3/4 | 20 × 2 F 4 J -------------|----------------------------------------------------- 54-406 | 20 × 2.00 -------------|----------------------------------------------------- 54-428 | 20 × 2 -------------|----------------------------------------------------- 54-559 | 26 × 2.00 -------------|----------------------------------------------------- 54-571 | 26 × 1 3/4 × 2 | 26 × 2 × 1 3/4 | 26 × 2 650 × 50 C -------------|----------------------------------------------------- 54-584 | 26 × 2 × 2 1/2 | 26 × 1 1/2 × 2 -------------|----------------------------------------------------- 54-609 | 28 × 2 -------------|----------------------------------------------------- 57-239 | 300 × 55 A -------------|----------------------------------------------------- 57-251 T | 315 × 55 -------------|----------------------------------------------------- 57-305 | 16 × 2.125 | 16 × 2.125 × 2 -------------|----------------------------------------------------- 57-390 | 450 × 55 A -------------|----------------------------------------------------- 57-406 | 20 × 2.125 | 20 × 2.125 × 2 -------------|----------------------------------------------------- 57-507 | 24 × 2.125 | 24 × 2.125 × 2 -------------|----------------------------------------------------- 57-559 | 26 × 2.125 | 26 × 2.125 × 2 -------------|----------------------------------------------------- 62-203 | 12 1/2 × 2 1/4 320 × 57 -------------|----------------------------------------------------- 62-305 | 16 × 2.125 -------------|----------------------------------------------------- 67-203 | 13 × 2 1/2 330 × 65 -------------|----------------------------------------------------- 67-381 | 20 × 2 1/2 -------------|-----------------------------------------------------
ISO 5775-2 defines designations for bicycle rims. It distinguishes between straight-side (SS), hooked-bead (HB) and crotchet-type (C) rims. Rims are designated by their nominal rim diameter and their nominal width, separated by a cross (×). The rim type codes SS or HB precede the rim designation, whereas the code C follows 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).
Standard straight-side rim widths:
18, 20, 22, 24, 27, 30.5
Standard straight-side and crotchet-type rim diameters:
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, 484, 489, 490, 498, 501, 507, 520, 531, 534, 540, 541, 547, 559, 565, 571, 584, 590, 597, 609, 622, 630, 635, 642
Standard hooked bead rim widths:
20, 25, 27
Standard hooked bead rim diameters:
270, 321, 372, 422, 459, 473, 510, 524, 560, 575, 611
Standard crotchet type rims widths:
13C, 15C, 16C, 17C, 19C, 21C, 23C, 25C