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). It is designed to make tire sizing consistent and clear. It replaces 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. 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, addressing 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

  1. clincher tyres mounted on straight sided type or crochet type rims, and
  2. 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 inner diameter of the tire when it is mounted on the rim. 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

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
MinMaxMinMax
1819151315
2021151317
2224171320
2527191322
2828191523
2934211625
3546231727
4757251730
5865302135
6671352543
7283453153
8495554164
96113765989
1141329472100

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 fewer mm than a 27-inch tire. 584 mm tires are also marketed as 27.5-inch (outer diameter) tires. Older markings of wired-edge tires can be converted to ISO 5775 designations with the help of the following table:

conversion table
Tire size
designation		Old marking, outer diameterrim diam.
InchesMillimetresmm
28-59026 × 1+3⁄8 × 1+1⁄8590
28-62228 × 1+5⁄8 × 1+1⁄8700 × 28 C622
28 × 1+5⁄8 × 1+1⁄4 × 1+1⁄8700 C Carrera622
28-63027 × 1+1⁄4630
28-63528 × 1+1⁄2700 B635
28-64228 × 1+3⁄8 × 1+1⁄8700 × 28 A642
32-23912 × 1+3⁄8 × 1+1⁄4300 × 32239
32-24812 × 1+1⁄4300 × 32 A248
32-28814 × 1+3⁄8 × 1+1⁄4350 × 32288
32-29814 × 1+1⁄4350 × 32 A298
32-34016 × 1+3⁄8 × 1+1⁄4400 A340
400 × 32340
32-34916 × 1+1⁄4 NL400 × 32 A349
32-35717 × 1+1⁄4357
32-36917 × 1+1⁄4369
32-39018 × 1+3⁄8 × 1+1⁄4450 A390
450 × 32390
32-40018 × 1+1⁄4450 × 32 A400
32-40620 × 1+1⁄4406
32-438500 × 32 ANL438
32-44020 × 1+3⁄8 × 1+1⁄4500 A440
500 × 32440
32-45120 × 1+1⁄4500 × 32 A451
32-489550 × 32 ANL489
32-49022 × 1+3⁄8 × 1+1⁄4550 A490
550 × 32490
32-50122 × 1+1⁄4550 × 32 A501
32-50822 × 1+1⁄4 × 1508
32-54024-1+3⁄8 × 1+1⁄4540
32-54124 × 1+3⁄8 × 1+1⁄4 NL600 A541
600 × 32 A541
32-54724 × 1+1⁄4547
32-59026 × 1+3⁄8 1+1⁄4650 × 32 A590
32-59726 × 1+1⁄4597
32-62228 × 1+5⁄8 × 1+1⁄4700 × 32 C622
28 × 1+1⁄4 × 1+3⁄4700 × C Course622
32-63027 × 1+1⁄4630
32-63528 × 1+1⁄2 × 1+1⁄8700 × 28 B635
700 B Course635
37-288350 A Comfort288
350 A 1⁄2 Balloon288
37-29814 × 1+3⁄8298
37-33716 × 1+3⁄8 ANL337
37-34016 × 1+3⁄8 NL400 A Comfort340
400 A 1⁄2 Balloon340
400 × 42 A340
400 × 35 A340
37-34916 × 1+3⁄8 NL349
37-38718 × 1+3⁄8387
37-390450 A Comfort390
450 A 1⁄2 Balloon390
37-40018 × 1+3⁄8400
37-40620 × 1+3⁄8406
37-43820 × 1+3⁄8 NL438
37-440500 A Comfort440
500 A 1⁄2 Balloon440
37-45120 × 1+3⁄8451
37-48922 × 1+3⁄8 NL489
37-490550 A Comfort490
550 A 1⁄2 Balloon490
37-49822 × 1+3⁄8 × 1+1⁄4 NL498
37-50122 × 1+3⁄8501
37-54024 × 1+3⁄8540
37-541600 A Comfort541
600 A 1⁄2 Balloon541
600 × 35 A541
37-56525 × 1+3⁄8565
37-58427.5 × 2.0 × 2.5584
26 × 1+3⁄8 × 1+1⁄2650 × 37 B584
37-59026 × 1+3⁄8650 A590
650 × 35 A590
37-62228 × 1+5⁄8 × 1+3⁄8700 × 35 C622
28 × 1+3⁄8 1+5⁄8622
37-64228 × 1+3⁄8700 × 35 A642
40-27914 × 1+1⁄2350 × 38 B279
40-28814 × 1+1⁄2 NL350 × 38288
40-33016 × 1+1⁄2400 × 38 B330
40-40620 × 1+1⁄2406
40-43220 × 1+1⁄2432
40-44020 × 1+1⁄2 NL500 × 38440
40-53424 × 1+1⁄2534
40-54024 × 1+3⁄8 × 1+1⁄2540
24 × 1+1⁄2 × 1+3⁄8540
40-55924 × 1.5559
40-57126 × 1+1⁄2 C.S.571
26 × 1+5⁄8 × 1+1⁄2 NL571
40-58426 × 1+1⁄2650 × 40 B584
650 × 38 B584
40-59026 × 1+3⁄8 × 1+1⁄2 NL590
40-62228 × 1+5⁄8 × 1+1⁄2 NL700 × 38 C622
40-63528 × 1+1⁄2 × 1+3⁄8700 B Standard635
28 × 1+1⁄2700 × 35 B635
700 × 38 B635
44-19410 × 1+5⁄8194
44-28814 × 1+3⁄8 × 1+5⁄8350 A288
350 × 42 A288
44-34016 × 1+5⁄8340
44-42820 × 1+5⁄8 × 1+1⁄2428
44-48422 × 1+5⁄8 × 1+1⁄2484
44-53124 × 1+5⁄8 × 1+1⁄2531
44-58426 × 1+1⁄2 × 1+5⁄8650 B Semi-comfort584
26 × 1+5⁄8 × 1+1⁄2650 B 1⁄2 Balloon584
26 × 1+3⁄4 × 1+1⁄2650 × 42 B584
44-62228 × 1+5⁄8700 × 42 C622
44-63528 × 1+5⁄8 × 1+1⁄2635
28 × 1+1⁄2 × 1+5⁄8635
45-58426 × 1.75 × 1+1⁄2650 × 45 B584
26 × 1+1⁄2 × 1+3⁄4584
47-20312+1⁄2 × 1.75 × 2+1⁄4203
47-22211 × 1+3⁄4222
47-30516 × 1.75 × 2305
47-31716 × 1+3⁄4317
47-35518 × 1.75 × 2355
47-40620 × 1.75 × 2406
20 × 1.75406
47-41920 × 1+3⁄4419
47-45722 × 1.75457
47-501 T24 × 1+3⁄4 R600 × 45 C501
47-50724 × 1.75 × 2507
24 × 1.75507
47-52024 × 1+3⁄4520
47-55926 × 1.75 × 2559
26 × 1.75559
47-57126 × 1+3⁄4650 × 45 C571
26 × 1+5⁄8650 C S.C.571
47-62228 × 1+3⁄4700 × 45 C622
28 × 1.75622
28 × 15⁄8 1+3⁄4622
50-40620 × 1.95406
52-40620 × 1.95406
54-29814 × 2 × 1+3⁄4298
54-30516 × 2305
54-40020 × 2 × 1+3⁄4400
20 × 2 F 4 J400
54-40620 × 2.00406
54-42820 × 2428
54-55926 × 2.00559
54-57126 × 1+3⁄4 × 2571
26 × 2 × 1+3⁄4571
26 × 2650 × 50 C571
54-58426 × 2 × 2+1⁄2584
26 × 1+1⁄2 × 2584
54-60928 × 2609
57-239300 × 55 A239
57-251 T315 × 55251
57-30516 × 2.125305
16 × 2.125 × 2305
57-390450 × 55 A390
57-40620 × 2.125406
20 × 2.125 × 2406
57-50724 × 2.125507
24 × 2.125 × 2507
57-55926 × 2.125559
26 × 2.125 × 2559
62-20312+1⁄2 × 2+1⁄4320 × 57203
62-30516 × 2.5305
67-20313 × 2+1⁄2330 × 65203
67-38120 × 2+1⁄2381

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

See also
  • Sheldon Brown. "Tire Sizing".
  • "Technical information – bicycle tyres" (PDF). Schwalbe.. handbook by a German tyre manufacturer, includes detailed size tables

References
  • International Standard ISO 5775-1:1997, Bicycle tyres and rims — Part 1: Tyre designations and dimensions
  • International Standard ISO 5775-2:1996, Bicycle tyres and rims — Part 2: Rims
  • JIS standard D 9421. (2009) (English): Bicycles — Rims
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