Sutherland’s handbook lists 79 different bicycle rim sizes ranging in size from 12’ to 28”. In addition there are numerous tires of different widths made to fit each rim diameter. The most common are 700C and 26”. What do these sizes mean and how did they become the most common sizes in the industry?
Most modern 700C tires do not measure 700 cm and most 26” tires do not measure 26” so what do the figures refer to?
To find the answer we must go back a few years before the globalization of the bike industry to the time when most countries had factories that produced bikes for their own domestic use. Each country had, over the years, developed bikes that were most suited to the local road and weather conditions and riders preferences. The majority of bikes made in France were fitted with 650B tires with large “demi-balon’ (half balloon) tires. These are large section tires, intended to be ridden at reasonably low pressure because almost every French town and village had cobbled streets (pave).
The smoother roads in Britain made the smaller section 26” x 13/8” the tire of choice.
In Holland where the big Dutch utility bikes still command the greatest share of the market the 28” x 11/2” is the most popular.
Every country had its preferences and developed it’s own tire dimensions.
The French and the British devised logical systems that were very similar. Let us look at the larger sizes as an example.
French British Bead seat diameter.
700A 28 x 11/4” 640 mm
700B 28 x 11/2” 635 mm
700C No UK equivalent 622 mm
No French equivalent 27 x 11/4” 630 mm.
No French equivalent 26 x 11/4” 597 mm
650A 26 x 13/8” 590 mm
650B 26 x 11/2” 584 mm
650C 26 x 13/4” 571 mm
Why the Brits decided to go with 27” instead of the 700C, I have no idea. It makes no sense, especially as 700C tubular wheels were in common use in the UK in the thirties when the 27” was introduced.
Originally all 700 tires had an overall diameter of 700 cm. (approximately 28”) but, as you will see from the bead seat diameters listed above, the rim diameters were smaller on the B and Cs. The section of the tire made up the difference. The 700A (28 x 11/4”) would have a relatively shallow 11/4” tire the 700B (28 x 11/2”) would have an 11/2” tire and the 700C would have a fat 13/4” tire. The overall diameter of them all, however, would be 700 cm. (28”).
The same relationship applied to the 650 (26”) tires, the 600 (24”), the 550 (22”) 500 (20”) 450 (18”) and 400 (16”).
All that made sense but then manufacturers started making different section tires to fit on rims not intended for them. We now have “700C” tires in all sections from 20 mm to 45 mm all with the same 622 mm bead seat diameter. This, of course, made nonsense of the whole system. Therefore, the European tire makers got together and devised a new sizing system for all bike tires. The bead seat diameter and the tire section designated tires. Therefore a 700C tire with a 23 mm section would be marked 622 -23. Where 622 is the bead seat diameter and 23 the section in millimeters. This system was subsequently adopted as the international standard (ISO). Most tires are marked with this designation, but few people refer to them that way.
To add to the confusion different countries used different designations for the same size tire. In Canada, a 28 x 11/2” tire is the same as a British 28 x 13/4” and therefore smaller than the British 28 x 11/2”. The US 26 x 1.75” bears no relationship to the British 26 x 13/4”.
Originally decimal inch designations referred to “clincher” tires and fractional inch dimensions referred to “wired on” tires. In the past most American tires were in fact “clinchers”. They had no wire bead but had rubber mouldings at the edge of the cover, which were “clinched” to hook edged rims. The decimal inch designation (26” x 2.125”, 26 x 1.75” etc.) signified that they were ‘clincher’ tires. True clincher tires are no longer made. What we refer to today, as clinchers are in fact wired-on tires, which are secured to the rim by a non-extensible steel wire, or more recently, Kevlar bead.
It was about that time that we got rid of all the anomalies and used the ISO tire designations. It really makes no sense that a 26” x 1.25” tire is a completely different size to a 26” x 11/4” and that a 28” x 11/2” in Canada is 3/4” smaller than a 28” x 11/2” in the UK.
Recently, in some circles, there has been a renewed interest in 650B tires. As I mentioned above many French bikes were built with this size as many French roads were cobbled. The large section 650Bs were ideal for these roads and also ideal for heavily loaded touring bikes and tandems. However with the globalization of the bike industry the American 26 x 1.75” has taken the place of the now almost obsolete 650B.
In recent years good quality road tires have been made in the American 26” size so why bother with the almost impossible to get 650B. The 26” rim is 25 mm smaller in diameter than the 650B but this has no effect on the performance of the bike. The only reason I can see to keep the 650B size going is to keep those lovely old French bikes on the road.
In recent years the industry has more or less standardized to 700C (622 mm) and 26” (559 mm) for adult bikes but we still have triathlon and smaller racing bikes designed with 650C (571 mm) wheels why not use 26” (559 mm) for these too?
The following, for what it is worth, is my suggestion for the complete range of rim diameters needed to cover the needs of the whole industry.
622 mm 700C All adult sport and lightweight bikes.
559 mm 26” City bikes, commuters, mountain bikes.
507 mm 24” Children’s and smaller person’s bikes.
457 mm 22” Children’s bikes.
406 mm 20” Children’s and folding bikes.
355 mm 18” Children’s and folding bikes.
305 mm 16” Children’s and folding bikes.
253 mm 14” Children’s bikes.
203 mm 12” Tiny children’s bikes.
That is nine rim sizes to replace the 79 listed in Sutherland’s. There will of course be a need for replacement rims and tires in the old sizes for those that wish to maintain vintage bikes but for the industry in general a reduction number of rim sizes has to be a huge benefit.
NOTE: Original article posted in Rivendell Reader. Since the article was written, 650B wheels and tires have become popular and more easily available. But to confuse matters, they are now being called 27.5’s which makes no sense as they are far smaller than 27″ wheels. And, 29’ers are in fact 700c wheels with larger section tires, adding a little more confusion to an already nonsensical subject.