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.

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
Nominal section width of tire	Straight-side rim	Crochet-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	-

Older markings

Older markings of wired-edge tires can be converted to ISO 5775 designations with the help of the following table:

Tire size designation	Old marking, outer diameter
Tire size designation	Inches	Millimetres
28-590	26 × 1⅜ × 1⅛
28-622	28 × 1⅝ × 1⅛	700 × 28 C
28-622	28 × 1⅝ × 1¼ × 1⅛	700 C Carrera
28-630	27 × 1¼ fifty
28-635	28 × 1½	700 B
28-642	28 × 1⅜ × 1⅛	700 × 28 A
32-239	12 × 1⅜ × 1¼	300 × 32
32-248	12 × 1¼	300 × 32 A
32-288	14 × 1⅜ × 1¼	350 × 32
32-298	14 × 1¼	350 × 32 A
32-340	16 × 1⅜ × 1¼	400 A
32-340		400 × 32
32-349	16 × 1¼ NL	400 × 32 A
32-357	17 × 1¼
32-369	16 × 1¼
32-390	18 × 1⅜ × 1¼	450 A
32-390		450 × 32
32-400	18 × 1¼	450 × 32 A
32-438		500 × 32 ANL
32-440	20 × 1⅜ × 1¼	500 A
32-440		500 × 32
32-451	20 × 1¼	500 × 32 A
32-489		550 × 32 ANL
32-490	22 × 1⅜ × 1¼	550 A
32-490		550 × 32
32-501	22 × 1¼	550 × 32 A
32-508	22 × 1¼ × 1
32-540	24-1⅜ × 1¼
32-541	24 × 1⅜ × 1¼ NL	600 A
32-541		600 × 32 A
32-547	24 × 1¼
32-590	26 × 1⅜ 1¼	650 × 32 A
32-597	26 × 1¼
32-622	28 × 1⅝ × 1¼	700 × 32 C
32-622	28 × 1¼ × 1¾	700 × C Course
32-630	27 × 1¼
32-635	28 × 1½ × 1⅛	700 × 28 B
32-635		700 B Course
37-288		350 A Comfort
37-288		350 A 1/2 Balloon
37-298	14 × 1⅜
37-337	16 × 1⅜ ANL
37-340	16 × 1⅜ NL	400 A Comfort
		400 A 1/2 Balloon
		400 × 42 A
		400 × 35 A
37-349	16 × 1⅜ NL
37-387	18 × 1⅜
37-390		450 A Comfort
37-390		450 A 1/2 Balloon
37-400	18 × 1⅜
37-438	20 × 1⅜ NL
37-440		500 A Comfort
37-440		500 A 1/2 Balloon
37-451	20 × 1⅜
37-489	22 × 1⅜ NL
37-490		550 A Comfort
37-490		550 A 1/2 Balloon
37-498	22 × 1⅜ × 1¼ NL
37-501	22 × 1⅜
37-540	24 × 1⅜
37-541		600 A Comfort
		600 A 1/2 Balloon
		600 × 35 A
37-565	25 × 1⅜
37-584	26 × 1½ × 1⅜
37-584	26 × 1⅜ × 1½
37-590	26 × 1⅜	650 A
37-590		650 × 35 A
37-622	28 × 1⅝ × 1⅜	700 × 35 C
37-622	28 × 1⅜ 1⅝
37-642	28 × 1⅜	700 × 35 A
40-279	14 × 1½	350 × 38 B
40-288	14 × 1½ NL	350 × 38
40-330	16 × 1½	400 × 38 B
40-432	20 × 1½
40-440	20 × 1½ NL	500 × 38
40-534	24 × 1½
40-540	24 × 1⅜ × 1½
40-540	24 × 1½ × 1⅜
40-571	26 × 1½ C.S.
40-571	26 × 1⅝ × 1½ NL
40-584	26 × 1½	650 × 35 B
40-584		650 × 38 B
40-590	26 × 1⅜ × 1½ NL
40-622	28 × 1⅝ × 1½ NL	700 × 38 C
40-635	28 × 1½ × 1⅜	700 B Standard
	28 × 1½	700 × 35 B
		700 × 38 B
44-194	10 × 1⅝
44-288	14 × 1⅜ × 1⅝	350 A
44-288		350 × 42 A
44-340	16 × 1⅝
44-428	20 × 1⅝ × 1½
44-484	22 × 1⅝ × 1½
44-531	24 × 1⅝ × 1½
44-584	26 × 1½ × 1⅝	650 B Semi-comfort
	26 × 1⅝ × 1½	650 B 1/2 Balloon
	26 × 1¾ × 1½	650 × 42 B
44-622	28 × 1⅝	700 × 42 C
44-635	28 × 1⅝ × 1½
44-635	28 × 1½ × 1⅝
45-584	26 × 1.75 × 1½	650 × 45 B
45-584	26 × 1½ × 1¾
47-203	12½ × 1.75 × 2¼
47-222	11 × 1¾
47-305	16 × 1.75 × 2
47-317	16 × 1¾
47-355	18 × 1.75 × 2
47-406	20 × 1.75 × 2
47-406	20 × 1.75
47-419	20 × 1¾
47-501 T	24 × 1¾ R	600 × 45 C
47-507	24 × 1.75 × 2
47-507	24 × 1.75
47-520	24 × 1¾
47-559	26 × 1.75 × 2
47-559	26 × 1.75
47-571	26 × 1¾	650 × 45 C
47-571	26 × 1⅝	650 C S.C.
47-622	28 × 1¾	700 × 45 C
	28 × 1.75
	28 × 15/8 1¾
50-406	20 × 1.95
52-406	20 × 1.95
54-298	14 × 2 × 1¾
54-305	16 × 2
54-400	20 × 2 × 1¾
54-400	20 × 2 F 4 J
54-406	20 × 2.00
54-428	20 × 2
54-559	26 × 2.00
54-571	26 × 1¾ × 2
	26 × 2 × 1¾
	26 × 2	650 × 50 C
54-584	26 × 2 × 2½
54-584	26 × 1½ × 2
54-609	28 × 2
57-239		300 × 55 A
57-251 T		315 × 55
57-305	16 × 2.125
57-305	16 × 2.125 × 2
57-390		450 × 55 A
57-406	20 × 2.125
57-406	20 × 2.125 × 2
57-507	24 × 2.125
57-507	24 × 2.125 × 2
57-559	26 × 2.125
57-559	26 × 2.125 × 2
62-203	12½ × 2¼	320 × 57
62-305	16 × 2.125
67-203	13 × 2½	330 × 65
67-381	20 × 2½

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

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 standard diameters of straight-side and crochet-type rims 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, 484, 489, 490, 498, 501, 507, 520, 531, 534, 540, 541, 547, 559, 565, 571, 584, 590, 597, 609, 622, 630, 635, 642

The standard diameters of hooked-bead rims are:

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

External links

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

ISO standards by standard number

List of ISO standards / ISO romanizations / IEC standards

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