# 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]
350 14 28 (Carrera) 1⅛ A 1⅜
400 16 32 (Course) B
450 18 35 (Confort)
37 (Demi-Ballon)
1⅜ C 1⅝
500 20 38
550 22 42 1⅝
575 23 45
600 24 50 2
650 26 55
700 28 65

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

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.