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.

Tires

Wired-edge tires

Wired-edge tires can be mounted on straight-side or crochet-type (aka hook bead) rims. Crochet-type rims are not the same as hooked-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 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

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 diameter		rim diam.
	Inches	Millimetres	mm
28-590	26 × 1⅜ × 1⅛		590
28-622	28 × 1⅝ × 1⅛	700 × 28 C	622
	28 × 1⅝ × 1¼ × 1⅛	700 C Carrera	622
28-630	27 × 1¼		630
28-635	28 × 1½	700 B	635
28-642	28 × 1⅜ × 1⅛	700 × 28 A	642
32-239	12 × 1⅜ × 1¼	300 × 32	239
32-248	12 × 1¼	300 × 32 A	248
32-288	14 × 1⅜ × 1¼	350 × 32	288
32-298	14 × 1¼	350 × 32 A	298
32-340	16 × 1⅜ × 1¼	400 A	340
		400 × 32	340
32-349	16 × 1¼ NL	400 × 32 A	349
32-357	17 × 1¼		357
32-369	17 × 1¼		369
32-390	18 × 1⅜ × 1¼	450 A	390
		450 × 32	390
32-400	18 × 1¼	450 × 32 A	400
32-406	20 × 1¼		406
32-438		500 × 32 ANL	438
32-440	20 × 1⅜ × 1¼	500 A	440
		500 × 32	440
32-451	20 × 1¼	500 × 32 A	451
32-489		550 × 32 ANL	489
32-490	22 × 1⅜ × 1¼	550 A	490
		550 × 32	490
32-501	22 × 1¼	550 × 32 A	501
32-508	22 × 1¼ × 1		508
32-540	24-1⅜ × 1¼		540
32-541	24 × 1⅜ × 1¼ NL	600 A	541
		600 × 32 A	541
32-547	24 × 1¼		547
32-590	26 × 1⅜ 1¼	650 × 32 A	590
32-597	26 × 1¼		597
32-622	28 × 1⅝ × 1¼	700 × 32 C	622
	28 × 1¼ × 1¾	700 × C Course	622
32-630	27 × 1¼		630
32-635	28 × 1½ × 1⅛	700 × 28 B	635
		700 B Course	635
37-288		350 A Comfort	288
		350 A 1/2 Balloon	288
37-298	14 × 1⅜		298
37-337	16 × 1⅜ ANL		337
37-340	16 × 1⅜ NL	400 A Comfort	340
		400 A 1/2 Balloon	340
		400 × 42 A	340
		400 × 35 A	340
37-349	16 × 1⅜ NL		349
37-387	18 × 1⅜		387
37-390		450 A Comfort	390
		450 A 1/2 Balloon	390
37-400	18 × 1⅜		400
37-406	20 × 1⅜		406
37-438	20 × 1⅜ NL		438
37-440		500 A Comfort	440
		500 A 1/2 Balloon	440
37-451	20 × 1⅜		451
37-489	22 × 1⅜ NL		489
37-490		550 A Comfort	490
		550 A 1/2 Balloon	490
37-498	22 × 1⅜ × 1¼ NL		498
37-501	22 × 1⅜		501
37-540	24 × 1⅜		540
37-541		600 A Comfort	541
		600 A 1/2 Balloon	541
		600 × 35 A	541
37-565	25 × 1⅜		565
37-584	27.5 × 2.0 × 2.5		584
	26 × 1⅜ × 1½	650 × 37 B	584
37-590	26 × 1⅜	650 A	590
		650 × 35 A	590
37-622	28 × 1⅝ × 1⅜	700 × 35 C	622
	28 × 1⅜ 1⅝		622
37-642	28 × 1⅜	700 × 35 A	642
40-279	14 × 1½	350 × 38 B	279
40-288	14 × 1½ NL	350 × 38	288
40-330	16 × 1½	400 × 38 B	330
40-406	20 × 1½		406
40-432	20 × 1½		432
40-440	20 × 1½ NL	500 × 38	440
40-534	24 × 1½		534
40-540	24 × 1⅜ × 1½		540
	24 × 1½ × 1⅜		540
40-559	24 × 1.5		559
40-571	26 × 1½ C.S.		571
	26 × 1⅝ × 1½ NL		571
40-584	26 × 1½	650 × 40 B	584
		650 × 38 B	584
40-590	26 × 1⅜ × 1½ NL		590
40-622	28 × 1⅝ × 1½ NL	700 × 38 C	622
40-635	28 × 1½ × 1⅜	700 B Standard	635
	28 × 1½	700 × 35 B	635
		700 × 38 B	635
44-194	10 × 1⅝		194
44-288	14 × 1⅜ × 1⅝	350 A	288
		350 × 42 A	288
44-340	16 × 1⅝		340
44-428	20 × 1⅝ × 1½		428
44-484	22 × 1⅝ × 1½		484
44-531	24 × 1⅝ × 1½		531
44-584	26 × 1½ × 1⅝	650 B Semi-comfort	584
	26 × 1⅝ × 1½	650 B 1/2 Balloon	584
	26 × 1¾ × 1½	650 × 42 B	584
44-622	28 × 1⅝	700 × 42 C	622
44-635	28 × 1⅝ × 1½		635
	28 × 1½ × 1⅝		635
45-584	26 × 1.75 × 1½	650 × 45 B	584
	26 × 1½ × 1¾		584
47-203	12½ × 1.75 × 2¼		203
47-222	11 × 1¾		222
47-305	16 × 1.75 × 2		305
47-317	16 × 1¾		317
47-355	18 × 1.75 × 2		355
47-406	20 × 1.75 × 2		406
	20 × 1.75		406
47-419	20 × 1¾		419
47-457	22 × 1.75		457
47-501 T	24 × 1¾ R	600 × 45 C	501
47-507	24 × 1.75 × 2		507
	24 × 1.75		507
47-520	24 × 1¾		520
47-559	26 × 1.75 × 2		559
	26 × 1.75		559
47-571	26 × 1¾	650 × 45 C	571
	26 × 1⅝	650 C S.C.	571
47-622	28 × 1¾	700 × 45 C	622
	28 × 1.75		622
	28 × 15/8 1¾		622
50-406	20 × 1.95		406
52-406	20 × 1.95		406
54-298	14 × 2 × 1¾		298
54-305	16 × 2		305
54-400	20 × 2 × 1¾		400
	20 × 2 F 4 J		400
54-406	20 × 2.00		406
54-428	20 × 2		428
54-559	26 × 2.00		559
54-571	26 × 1¾ × 2		571
	26 × 2 × 1¾		571
	26 × 2	650 × 50 C	571
54-584	26 × 2 × 2½		584
	26 × 1½ × 2		584
54-609	28 × 2		609
57-239		300 × 55 A	239
57-251 T		315 × 55	251
57-305	16 × 2.125		305
	16 × 2.125 × 2		305
57-390		450 × 55 A	390
57-406	20 × 2.125		406
	20 × 2.125 × 2		406
57-507	24 × 2.125		507
	24 × 2.125 × 2		507
57-559	26 × 2.125		559
	26 × 2.125 × 2		559
62-203	12½ × 2¼	320 × 57	203
62-305	16 × 2.5		305
67-203	13 × 2½	330 × 65	203
67-381	20 × 2½		381

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 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

• Bicycle wheel

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
• JIS standard D 9421. (2009) (English): Bicycles — Rims