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International standard for labeling the size of bicycle tires and rims
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. 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:
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 (25mm 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 30mm and 55% for those larger.
The section height of a tire is usually identical to its section width (for tires less than 28mm, 2.5mm 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. 584mm 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 × 1+3⁄8 × 1+1⁄8
622
28-622
28 × 1+5⁄8 × 1+1⁄8
700 × 28 C
622
28 × 1+5⁄8 × 1+1⁄4 × 1+1⁄8
700 C Carrera
630
28-630
27 × 1+1⁄4
635
28-635
28 × 1+1⁄2
700 B
642
28-642
28 × 1+3⁄8 × 1+1⁄8
700 × 28 A
239
32-239
12 × 1+3⁄8 × 1+1⁄4
300 × 32
248
32-248
12 × 1+1⁄4
300 × 32 A
288
32-288
14 × 1+3⁄8 × 1+1⁄4
350 × 32
298
32-298
14 × 1+1⁄4
350 × 32 A
340
32-340
16 × 1+3⁄8 × 1+1⁄4
400 A
340
400 × 32
349
32-349
16 × 1+1⁄4 NL
400 × 32 A
357
32-357
17 × 1+1⁄4
369
32-369
17 × 1+1⁄4
390
32-390
18 × 1+3⁄8 × 1+1⁄4
450 A
390
450 × 32
400
32-400
18 × 1+1⁄4
450 × 32 A
406
32-406
20 × 1+1⁄4
438
32-438
500 × 32 ANL
440
32-440
20 × 1+3⁄8 × 1+1⁄4
500 A
440
500 × 32
451
32-451
20 × 1+1⁄4
500 × 32 A
489
32-489
550 × 32 ANL
490
32-490
22 × 1+3⁄8 × 1+1⁄4
550 A
490
550 × 32
501
32-501
22 × 1+1⁄4
550 × 32 A
508
32-508
22 × 1+1⁄4 × 1
540
32-540
24-1+3⁄8 × 1+1⁄4
541
32-541
24 × 1+3⁄8 × 1+1⁄4 NL
600 A
541
600 × 32 A
547
32-547
24 × 1+1⁄4
590
32-590
26 × 1+3⁄81+1⁄4
650 × 32 A
597
32-597
26 × 1+1⁄4
622
32-622
28 × 1+5⁄8 × 1+1⁄4
700 × 32 C
622
28 × 1+1⁄4 × 1+3⁄4
700 × C Course
630
32-630
27 × 1+1⁄4
635
32-635
28 × 1+1⁄2 × 1+1⁄8
700 × 28 B
635
700 B Course
288
37-288
350 A Comfort
288
350 A 1⁄2 Balloon
298
37-298
14 × 1+3⁄8
337
37-337
16 × 1+3⁄8 ANL
340
37-340
16 × 1+3⁄8 NL
400 A Comfort
340
400 A 1⁄2 Balloon
340
400 × 42 A
340
400 × 35 A
349
37-349
16 × 1+3⁄8 NL
387
37-387
18 × 1+3⁄8
390
37-390
450 A Comfort
390
450 A 1⁄2 Balloon
400
37-400
18 × 1+3⁄8
406
37-406
20 × 1+3⁄8
438
37-438
20 × 1+3⁄8 NL
440
37-440
500 A Comfort
440
500 A 1⁄2 Balloon
451
37-451
20 × 1+3⁄8
489
37-489
22 × 1+3⁄8 NL
490
37-490
550 A Comfort
490
550 A 1⁄2 Balloon
498
37-498
22 × 1+3⁄8 × 1+1⁄4 NL
501
37-501
22 × 1+3⁄8
540
37-540
24 × 1+3⁄8
541
37-541
600 A Comfort
541
600 A 1⁄2 Balloon
541
600 × 35 A
565
37-565
25 × 1+3⁄8
584
37-584
27.5 × 2.0 × 2.5
584
26 × 1+3⁄8 × 1+1⁄2
650 × 37 B
590
37-590
26 × 1+3⁄8
650 A
590
650 × 35 A
622
37-622
28 × 1+5⁄8 × 1+3⁄8
700 × 35 C
622
28 × 1+3⁄81+5⁄8
642
37-642
28 × 1+3⁄8
700 × 35 A
279
40-279
14 × 1+1⁄2
350 × 38 B
288
40-288
14 × 1+1⁄2 NL
350 × 38
330
40-330
16 × 1+1⁄2
400 × 38 B
406
40-406
20 × 1+1⁄2
432
40-432
20 × 1+1⁄2
440
40-440
20 × 1+1⁄2 NL
500 × 38
534
40-534
24 × 1+1⁄2
540
40-540
24 × 1+3⁄8 × 1+1⁄2
540
24 × 1+1⁄2 × 1+3⁄8
559
40-559
24 × 1.5
571
40-571
26 × 1+1⁄2 C.S.
571
26 × 1+5⁄8 × 1+1⁄2 NL
584
40-584
26 × 1+1⁄2
650 × 40 B
584
650 × 38 B
590
40-590
26 × 1+3⁄8 × 1+1⁄2 NL
622
40-622
28 × 1+5⁄8 × 1+1⁄2 NL
700 × 38 C
635
40-635
28 × 1+1⁄2 × 1+3⁄8
700 B Standard
635
28 × 1+1⁄2
700 × 35 B
635
700 × 38 B
194
44-194
10 × 1+5⁄8
288
44-288
14 × 1+3⁄8 × 1+5⁄8
350 A
288
350 × 42 A
340
44-340
16 × 1+5⁄8
428
44-428
20 × 1+5⁄8 × 1+1⁄2
484
44-484
22 × 1+5⁄8 × 1+1⁄2
531
44-531
24 × 1+5⁄8 × 1+1⁄2
584
44-584
26 × 1+1⁄2 × 1+5⁄8
650 B Semi-comfort
584
26 × 1+5⁄8 × 1+1⁄2
650 B 1⁄2 Balloon
584
26 × 1+3⁄4 × 1+1⁄2
650 × 42 B
622
44-622
28 × 1+5⁄8
700 × 42 C
635
44-635
28 × 1+5⁄8 × 1+1⁄2
635
28 × 1+1⁄2 × 1+5⁄8
584
45-584
26 × 1.75 × 1+1⁄2
650 × 45 B
584
26 × 1+1⁄2 × 1+3⁄4
203
47-203
12+1⁄2 × 1.75 × 2+1⁄4
222
47-222
11 × 1+3⁄4
305
47-305
16 × 1.75 × 2
317
47-317
16 × 1+3⁄4
355
47-355
18 × 1.75 × 2
406
47-406
20 × 1.75 × 2
406
20 × 1.75
419
47-419
20 × 1+3⁄4
457
47-457
22 × 1.75
501
47-501 T
24 × 1+3⁄4 R
600 × 45 C
507
47-507
24 × 1.75 × 2
507
24 × 1.75
520
47-520
24 × 1+3⁄4
559
47-559
26 × 1.75 × 2
559
26 × 1.75
571
47-571
26 × 1+3⁄4
650 × 45 C
571
26 × 1+5⁄8
650 C S.C.
622
47-622
28 × 1+3⁄4
700 × 45 C
622
28 × 1.75
622
28 × 15⁄81+3⁄4
406
50-406
20 × 1.95
406
52-406
20 × 1.95
559
53-559
26 × 1.95
298
54-298
14 × 2 × 1+3⁄4
305
54-305
16 × 2
400
54-400
20 × 2 × 1+3⁄4
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 × 1+3⁄4 × 2
571
26 × 2 × 1+3⁄4
571
26 × 2
650 × 50 C
584
54-584
26 × 2 × 2+1⁄2
584
26 × 1+1⁄2 × 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
12+1⁄2 × 2+1⁄4
320 × 57
305
62-305
16 × 2.5
203
67-203
13 × 2+1⁄2
330 × 65
381
67-381
20 × 2+1⁄2
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
This section needs expansion. You can help by adding to it. (May 2008)
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:
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