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 standard JIS D 9421 specifies the same dimensional system, but adds details on additional rim types and also specifies additional parameters such as rim strength and details of spoke holes.

Tires

Wired-edge tires

Wired-edge tires can be mounted on straight-side or crochet-type (aka hook bead) rims. Such tires are designated with their nominal 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 a set of nominal section widths for wired-edge tires and lists recommended rim widths for each:

Nominal section
width of tire
Recommended rim widths
Straight-side rimCrochet-type rim
16-13C
18-13C
20-13C
231613C, 15C
2516, 1813C, 15C, 17C
2816, 18, 2015C, 17C, 19C
3216, 18, 2015C, 17C, 19C
3518, 20, 2217C, 19C, 21C
3718, 20, 2217C, 19C, 21C
4020, 22, 2419C, 21C, 23C
4420, 22, 24, 2719C, 21C, 23C, 25C
4720, 22, 24, 2719C, 21C, 23C, 25C
5022, 24, 27, 30.521C, 23C, 25C
5427, 30.525C
5727, 30.525C
6227, 30.5-

Older markings

Note how in the below sorted table the "inches" measure is inconsistent with the mm measures, if height varies: Some 28" tires then have less mm than a 27" tire. 584 mm tires are also marketed as 27.5" (outer diam.) 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 × 1⅜ × 1⅛590
28-62228 × 1⅝ × 1⅛700 × 28 C622
28 × 1⅝ × 1¼ × 1⅛700 C Carrera622
28-63027 × 1¼ fifty630
28-63528 × 1½700 B635
28-64228 × 1⅜ × 1⅛700 × 28 A642
32-23912 × 1⅜ × 1¼300 × 32239
32-24812 × 1¼300 × 32 A248
32-28814 × 1⅜ × 1¼350 × 32288
32-29814 × 1¼350 × 32 A298
32-34016 × 1⅜ × 1¼400 A340
400 × 32340
32-34916 × 1¼ NL400 × 32 A349
32-35717 × 1¼357
32-36917 × 1¼369
32-39018 × 1⅜ × 1¼450 A390
450 × 32390
32-40018 × 1¼450 × 32 A400
32-40620 × 1¼406
32-438500 × 32 ANL438
32-44020 × 1⅜ × 1¼500 A440
500 × 32440
32-45120 × 1¼500 × 32 A451
32-489550 × 32 ANL489
32-49022 × 1⅜ × 1¼550 A490
550 × 32490
32-50122 × 1¼550 × 32 A501
32-50822 × 1¼ × 1508
32-54024-1⅜ × 1¼540
32-54124 × 1⅜ × 1¼ NL600 A541
600 × 32 A541
32-54724 × 1¼547
32-59026 × 1⅜ 1¼650 × 32 A590
32-59726 × 1¼597
32-62228 × 1⅝ × 1¼700 × 32 C622
28 × 1¼ × 1¾700 × C Course622
32-63027 × 1¼630
32-63528 × 1½ × 1⅛700 × 28 B635
700 B Course635
37-288350 A Comfort288
350 A 1/2 Balloon288
37-29814 × 1⅜298
37-33716 × 1⅜ ANL337
37-34016 × 1⅜ NL400 A Comfort340
400 A 1/2 Balloon340
400 × 42 A340
400 × 35 A340
37-34916 × 1⅜ NL349
37-38718 × 1⅜387
37-390450 A Comfort390
450 A 1/2 Balloon390
37-40018 × 1⅜400
37-40620 × 1⅜406
37-43820 × 1⅜ NL438
37-440500 A Comfort440
500 A 1/2 Balloon440
37-45120 × 1⅜451
37-48922 × 1⅜ NL489
37-490550 A Comfort490
550 A 1/2 Balloon490
37-49822 × 1⅜ × 1¼ NL498
37-50122 × 1⅜501
37-54024 × 1⅜540
37-541600 A Comfort541
600 A 1/2 Balloon541
600 × 35 A541
37-56525 × 1⅜565
37-58426 × 1½ × 1⅜584
26 × 1⅜ × 1½650 x 37 B584
37-59026 × 1⅜650 A590
650 × 35 A590
37-62228 × 1⅝ × 1⅜700 × 35 C622
28 × 1⅜ 1⅝622
37-64228 × 1⅜700 × 35 A642
40-27914 × 1½350 × 38 B279
40-28814 × 1½ NL350 × 38288
40-33016 × 1½400 × 38 B330
40-40620 × 1½406
40-43220 × 1½432
40-44020 × 1½ NL500 × 38440
40-53424 × 1½534
40-54024 × 1⅜ × 1½540
24 × 1½ × 1⅜540
40-55924 × 1.5559
40-57126 × 1½ C.S.571
26 × 1⅝ × 1½ NL571
40-58426 × 1½650 × 40 B584
650 × 38 B584
40-59026 × 1⅜ × 1½ NL590
40-62228 × 1⅝ × 1½ NL700 × 38 C622
40-63528 × 1½ × 1⅜700 B Standard635
28 × 1½700 × 35 B635
700 × 38 B635
44-19410 × 1⅝194
44-28814 × 1⅜ × 1⅝350 A288
350 × 42 A288
44-34016 × 1⅝340
44-42820 × 1⅝ × 1½428
44-48422 × 1⅝ × 1½484
44-53124 × 1⅝ × 1½531
44-58426 × 1½ × 1⅝650 B Semi-comfort584
26 × 1⅝ × 1½650 B 1/2 Balloon584
26 × 1¾ × 1½650 × 42 B584
44-62228 × 1⅝700 × 42 C622
44-63528 × 1⅝ × 1½635
28 × 1½ × 1⅝635
45-58426 × 1.75 × 1½650 × 45 B584
26 × 1½ × 1¾584
47-20312½ × 1.75 × 2¼203
47-22211 × 1¾222
47-30516 × 1.75 × 2305
47-31716 × 1¾317
47-35518 × 1.75 × 2355
47-40620 × 1.75 × 2406
20 × 1.75406
47-41920 × 1¾419
47-45722 x 1.75457
47-501 T24 × 1¾ R600 × 45 C501
47-50724 × 1.75 × 2507
24 × 1.75507
47-52024 × 1¾520
47-55926 × 1.75 × 2559
26 × 1.75559
47-57126 × 1¾650 × 45 C571
26 × 1⅝650 C S.C.571
47-62228 × 1¾700 × 45 C622
28 × 1.75622
28 × 15/8 1¾622
50-40620 × 1.95406
52-40620 × 1.95406
54-29814 × 2 × 1¾298
54-30516 × 2305
54-40020 × 2 × 1¾400
20 × 2 F 4 J400
54-40620 × 2.00406
54-42820 × 2428
54-55926 × 2.00559
54-57126 × 1¾ × 2571
26 × 2 × 1¾571
26 × 2650 × 50 C571
54-58426 × 2 × 2½584
26 × 1½ × 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
62-20312½ × 2¼320 × 57203
62-30516 × 2.5305
67-20313 × 2½330 × 65203
67-38120 × 2½381


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

ISO 5775-2 defines designations for bicycle rims. It distinguishes between

  • Straight-side (SS) rims
  • Crochet-type (C) 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 hooked bead 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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