Dagworth and District Gentlemen's Cycling Society

A guide to tyre sizes

Potted History

Before World War Two all tyres were measured in the same way, whether they were for lorries, cars, motor cycles, pedal cycles or wheelbarrows. This size was expressed as two numbers: the first being the overall diameter of the tread and the second being the height of the tread above the wheel rim; eg: 28×1½. If, for some reason, you wanted to know the rim diameter you just doubled the second figure and subtracted it from the first; eg: a 28×1½ tyre fits a rim 28 - (2×1½) = 25 inches in diameter. Of course, this meant that a 28×1¾ tyre could not be put onto a 28×1½ rim but, since no one was daft enough to try it, this didn’t really matter. This system was simple and easy to understand; therefore it had to be changed.

An early attempt to add confusion to the system was the introduction of ‘Carrier Oversize’ tyres; eg: 26×2×1¾ is a 2" section tyre that fits a 26×1¾ rim. Carrier tyres seem to be the only ones that use this system (though 20×1¾×2 tyres for low gravity carriers don't fit into any known system), all other oversize or undersize tyres being measured the other way round; ie: a 26×1½×1¾ tyre fits a 26×1½ rim.

Going Metric

In France the metric system was adopted so metric tyre sizes were introduced. The tyres were really the same size of course, so a nominal conversion factor of 25mm = 1 inch was used. The following conversion tables can be used to swap between the two systems.

Dia	Dia	Actual Section		Nominal Section
(mm)	(in)	(mm)	(in)	(mm)	(in)
300	12	25	1	[none]	1¼
350	14	28 (Carrera)	1⅛	A	1⅜
400	16	32 (Course)	1¼	B	1½
450	18	35 (Confort) 37 (Demi-Ballon)	1⅜	C	1⅝
500	20	38	1½
550	22	42	1⅝
575	23	45	1¾
600	24	50	2
650	26	55	2¼
700	28	65	2½

Thus a 650×35A converts to 26×1⅜ and a 700×35C to 28×1⅝×1⅜. The advantage of this system is that it is easy to tell which sizes will fit which rim. Any 700C tyre will go onto any 700C rim—but avoid putting very wide tyres on narrow rims and vice versa.

This page is about pedal cycle tyres but a quick word about French motor cycle tyres won’t go amiss here. Old French motor cycle tyres use a similar-looking system but it’s not quite the same—it doesn’t have the final letter. So, for example, a 600×65 equates to a 24×2½ or 2.50–19.

This metric system, although universal in France, seems to have gained less of a foothold in other parts of Europe. What I shall call, for want of a better name, the ‘German’ system uses imperial measurements in a bizarre mixture of fractions and decimals. So far I have been unable to deduce any logical sequence to the system.

The 1⅝ nominal section is really 1¾—please don’t ask why or I might burst into tears. Which means that a 700C tyre, although it may also be marked as 28×1⅝ will fit on an old British 28×1¾ rim.

Modern Times

Motor vehicle tyres adopted a new system after World War Two. The first figure being the tyre width and the second being the rim diameter. To highlight the difference between new and old systems, decimal fractions were used for the tyre width. A few moped tyre sizes that are similar to pedal cycle tyre sizes are shown in the main table.

Another drift away from the original system occurred at the end of the 1930s with the introduction of the well-known 27×1¼ tyre. (Note: there was a 27×1¼ before this but it had already become obsolete when this later version was introduced. If you have a cycle with this pre-1930s 27×1¼ size of wheels, the bad news is that the later tyres won’t fit—but the very good news is that 700C tyres will.) There are several 27" sizes which all use the same rim diameter; so these are not using the traditional system of measurement even though they look as if they are. The same applies to the ‘Moulton–Wolber’ 17×1¼ tyre: a sort of miniature 27×1¼.

All Change

The trouble with bicycles is that they last for a very long time. In order to sell more bicycles the industry has to find a way of forcing people to buy them. Fashion has been a powerful force here and many people have bought ‘Mountain Bikes’ which are totally unsuitable for the uses they are put to. Another wheeze has been to introduce a new range of cycle tyres and gradually withdraw the old ones, so a new bike is needed when the old one’s tyres wear out. A cunning feature of the new Imperial sizes is that none of the numbers used bears any relation to an actual measurement; however, to start with, the system was based on rim diameters of a whole number of inches. A 26×2.00 tyre and a 26×2 tyre are interchangeable since both use a 22" rim. A 26×1.75 tyre has a rim diameter of 22" so will not fit a 26×1¾ rim but will fit a 26×2 rim, as will a 26×2.125 tyre. It’s probably best not to try thinking about sizes like 12½×1.75×2¼. This new system seems to have originated in the USA but with a few German sizes thrown in to confuse.

Having mentioned the USA, I suppose it’s time to describe their tyre sizes. In America everything is bigger - or so Americans would like to think. To preserve this illusion the sizes written on the sides of American tyres are larger than the tyres really are.

Once the ‘26’ size had taken over the MTB market, it was time to change again: enter the ‘29er’ Mountain Bike. These ‘29-inch’ disrupt the whole-inch rim diameter pattern because they’re not really a new size at all: they’re the good old 700C size repackaged. Close on the heels of the 29 size came 27½. Again, this is based on an old size: 650B.

Solids

At repeating intervals throughout the history of the bicycle, enterprising manufacturers have come up with ‘puncture-proof’ tyres by the simple expedient of making them from solid rubber. After a short time, people realise how bad they are and they vanish again. However, modern plastic technology is getting closer to making a decent solid tyre and one of the latest incarnations of this idea, produced by the Green Tyre Co, seems to be lasting longer than its predecessors did. For the collector with a large number of cycles, or a museum, solid tyres can be a good solution to the problem of keeping a large number of tyres inflated on seldom-used bikes. Green Tyres use the same mixture of measurements as everyone else except they call their 26×1⅜ tyre a 26×1.375. Unlike pneumatic tyres, solids also have to be the right width for the rim—so, for instance, a 26×1.375 tyre won’t squeeze in to a Dunlop 26×1⅜ Narrow rim.

Tyres you can trust

Since tyre manufacturers do not want to suffer the same confusion they have foisted onto the rest of us, they use their own system of ‘ETRTO’ sizes, which show the actual tyre width and rim diameter in millimetres. The ETRTO system was also adopted as the basis of ISO 5775 so, if you see a size described as ‘ISO’, this is the same thing. The ETRTO size is, nowadays, about the only measurement on a tyre that can be trusted to bear any resemblance to reality. If you’ve got an obscure size of rim and need to know which tyres will fit, measure all the way round the bead seat. Divide this measurement (in millimetres) by pi (3.14159265358979323846264 or thereabouts). Get a tyre with an ETRTO size whose second number is the same as your answer. There is one quirk in the ETRTO sizes: those based on the 24×1⅜ tyre are sometimes described as 540 and sometimes 541. Clearly, a 1mm variation in a tyre this big makes no discernible difference.

A table of cycle tyre size equivalents

ETRTO	Imperial	British (new)	French	Moped	American	German
47-94			200×47
44-194	10×1⅝
44-203		12½×1.75				12½×1.75
47-203		12½×1.75×2¼	320×47			12½×1.75×2¼
50-203	12×2	12×2.00	320×50	2.00–8
57-203	12½×2¼		320×57
62-203	12½×2¼		320×57
44-222	11×1¾×1⅝
47-222	11×1¾
32-239	12×1⅜×1¼		300×32A
32-248	12×1¼		300×32
57-251T	14½×2¼		315×55
50-267	14×2×1¾ Carrier
40-279	14×1½		350×38B
32-288	14×1⅜×1¼		350×32A
37-288	14×1⅜		350×37A 350A Confort 350A Demi-Ballon
40-288	14×1½NL	14×1.75
44-288	14×1⅜×1⅝	14×1.75	350A 350×42A
32-298		14×1¼	350×32
37-298	14×1⅜ Universal
44-305		16×1.75
47-305		16×1.75×2			16×1.75×2	16×1.75×2
54-305	16×2		400×50	2.00–12
62-305				2.25–12	16×2.125
47-317	16×1¾
40-330	16×1½		400×38B
37-337	16×1⅜ANL
32-340	16×1⅜×1¼		400A 400×32A
37-340	16×1⅜		400×35A 400A Confort 400A Demi-Ballon
44-340	16×1⅜×1⅝		400×42A
25-349	16×1 Primo
28-349	16×1¼NL		400×32
32-349	16×1⅜ Universal
37-349	16×1⅜ Universal
47-355		18×1.75×2
32-357						17×1¼
62-381	20×2½ Carrier
37-387	18×1⅜NL
37-387	18×1⅜NL
28-390			450B 450×28A
32-390	18×1⅜×1¼		450A 450×32A
37-390			450A Confort 450A Demi-Ballon
57-390T			450×55A
32-400	18×1¼		450×32
37-400	18×1⅜ Universal
44-400T	20×2×1¾ Carrier
36-406		20×1.50			20×1.50
37-406		20×1.50			20×1.50
44-406		20×1.75			20×1.75
47-406		20×1.75 20×1.75×2			20×1.75
54-406	20×2	20×2.125	500×50	2.00–16	20×2.125
57-406		20×2.125
47-419	20×1¾ (Crypto)				20×1¾ (Schwinn 20" S-7)
44-428	20×1⅝
40-432	20×1½
32-438	20×1⅜NL		500×32ANL
37-438	20×1⅜NL
28-440			500×28A
32-440	20×1⅜×1¼		500A 500×32A
37-440			500A Confort 500A Demi-Ballon 500×37A
40-440	20×1½NL		500×38A
47-440		18×1.75×2
25-451	20×1 Primo
28-451	20×1⅛
32-451	20×1¼		500×32
37-451	20×1⅜ Universal				(Schwinn 20" S-5/S-6)
50-456		22×2.00		2.00–18
44-484	22×1½					22×1⅝-1½
47-484	23×2		550×50B	2.00–19		23×2
54-483				2.25–19		23×2.25
32-489			550×32ANL			22×1¼NL
37-489						22×1⅜×1¼NL
28-490			550×28A
32-490	22×1⅜×1¼		550×32A
37-490	22×1⅜		550A 550A Confort 550A Demi-Ballon
32-501	22×1¼		550×32
37-501	22×1⅜ Universal
47-501T	24×1¾R
37-507					24×1.5
47-507	24×2×1¾	24×1.75 24×1.75×2		2.00–20	24×1.75	24×1.75/2
32-508					24×1.5	22×1¼×1
25-520	24×1		600×25C
28-520	24×1⅛		600×28C
47-520	24×1¾
44-531	24×1⅝×1½
35-534	24×1½		600×32B
37-534	24×1½×1¾		600×35B
40-534	24×1½		600×38B			24×1½
54-534	24×1½×2 25×2		600×50B 625×50	2.25–21
28-541			600×28A
32-540 32-541	24×1⅜×1¼ 24×1⅜×1¼NL		600×32A 600×32ANL			24×1¼×1⅜
37-540 37-541	24×1⅜		600A Confort 600A Demi-Ballon 600×35A			24×1⅜
40-540 37-541	24×1⅜×1½		600×38A			24×1½×1⅜
32-547	24×1¼		600A
32-559					26×1.25
37-559		26×1.5			26×1.5
44-559		26×1.75
47-559		26×1.95			26×1.75	26×1.75×2
50-559	26×2	26×2		2.25–22	26×2
54-559 54-559T	26×2	26×2.125		2.25–22	26×2.125 (Schwinn 26" S-2)
37-565	25×1⅜
57-567	This is an odd one
25-571	26×1⅝×1		650×25C			26×1.75×1
32-571	26×1⅝×1¼		650×32C			26×1.75×1¼
40-571	26×1⅝×1½NL 26×1½CS		650×38C
47-571 47-571T	26×1¾		650×45C 650C SC		26×1¾ (Schwinn 26" S-7)
54-571	26×2×1¾		650×50C			26×2×1¾
37-584	26×1½×1⅜		650×35B			26×1⅜×1½
40-584	26×1½		650B Standard 650×38B			26×1.5
44-584	26×1½×1⅝		650B Demi Confort 650BSC			26×1⅝×1½ 26×1¾-1½
47-584	26×1½×1¾		650×45B
50-584			650×50B		27½×2.0
55-584			650×55B		27½×2.2
60-584			650×60B		27½×2.4
28-590	26×1⅜×1⅛		650×28A
32-590	26×1⅜×1¼		650×32A			26×1¼×1⅜
35-590	26×1⅜
37-590	26×1⅜	26×1.375 (Green)	650A 650×35A			26×1⅜
40-590	26×1⅜×1½		650×38A			26×1½×1⅜
42-590	26×1⅜×1⅝		650×40A			26×1⅝×1⅜
32-597	26×1¼				26×1⅜ (Schwinn 26" S-5/S-6)	26×1¼
18-622			700×18C		700×19C
19-622			700×19C
20-622	28×1⅝×¾		700×20C			28×3/4
22-622			700×22C		700×25C
23-622	28×1⅝×1		700×23C			28×1
25-622			700×25C		700×28C
28-622	28×1⅝×1⅛ 28×1⅝×1¼×1⅛		700×28C 700C Carrera			28×1⅛×1¾
32-622	28×1⅝×1¼ 27×1¼ (pre-1930s)		700C Course 700×32C		700×35C	28×1¼×1¾
37-622	28×1⅝×1⅜		700×35C			28×1⅜×1⅝
40-622	28×1⅝×1½		700C 700×38C 700×40C			28×1½×1.75
44-622	28×1⅝		700×42C
47-622 47-622T	28×1⅝×1¾		700×45C			28×1.75 28×1¾
50-622	28×1⅝×2		700×50C		29×2.00
54-622					29×2.10
57-622					29×2.25
60-622					29×2.35
62-622					29×2.40
23-630		27×7/8 27×1
25-630		27×1			27×1⅛
28-630		27×1⅛ 27×1¼fifty			27×1¼
32-630		27×1¼			27×1⅜
37-630		27×1⅜
28-635	28×1½×1⅛		700×28B
32-635	28×1½×1¼		700×32B 700B Course
37-635	28×1½×1⅜		700×35B		28×1⅜×1½
40-635	28×1½		700B Standard 700×38B		28×1½
44-635	28×1½×1⅝		700×40B 700×42B			28×1.75×1½ 28×1⅝×1½
28-642	28×1⅜×1⅛		700×28A
37-642	28×1⅜		700×35A
32-645	28×1 ¼

Oddities

57–567 Tyre

57-567 Tyre

Here's a photo of a tyre I bought in Gabon in Africa just before the turn of the Milennium. I supposed that it would fit the wheels of my Raleigh Activator but was disappointed. (One needed 559 as the bead seat diameter for many straightforward "Mountain" bikes.) As a matter of principle after my tours of duty in Gabon I brought the bike and the tyre (I had bought two) back and still have it all.

Best regards,
Bob Stafford

Back to position in table

THE SMALL PRINT

The Dagworth & District Gentleman’s Cycling Society accepts no responsibility for anyone who believes this lot implicitly and, as a consequence, buys a tyre that won’t fit. The information (or misinformation) in this tyre guide has been cadged from a number of sources, but mainly Michelin Tyres, Vredestein Tyres, ISO 5775-1 and the Cyclists Touring Club.

Last Modified 10 November 2023