This article was written in 2011 and as a result, some information may be outdated.
Currently there are three main sizes for wheels (children’s bicycles aside). They are known as 26″ (now considered an old mountain bike standard), 650b (an MTB standard also used in some gravel bikes) and 700c (traditionally limited to road or touring use, but now widespread on MTB’s). Often these can equate to being a similar size when you consider how much bigger a 26″ tyre is and how skinny a 700c tyre can be. That makes a 29er, which is a mountain bike width tyre on a 700c diameter rim look and feel very large, even though the rim is the same size as a standard road rim.
This standardisation has made making wheels more much straightforward. Wheel builders and manufacturers can offer more options and more price points for a given function. However, there are a number of bikes out there that pre-date this standardisation. There are even a few using old fashioned sizes today still. Normally to keep the bike in line with tradition (for example Pashleys). Some people even believe that the standard wheel sizes are simply wrong and opt for something different.
When it comes to understanding wheels we need to be clear what were working with. The clearest measure is the ISO. See Sheldon Brown for a good article explaining all of these details http://www.sheldonbrown.com/tire-sizing.html. The ISO of a 26″ wheel 559. The ISO of a 700c is 622. Now we start to get a relevant comparison. Here are some important sizes:
559 – 26″ (Standard mountain bike)
571 – 26×1, 26×1 3/4, 650c
584 – 26×1 1/2, 650b
590 – 26×1 3/8, 650a
622 – 700c (Standard road/touring bike)
630 – 27×1, 27×1 1/7, 27×1 1/4
635 – 28×1 1/2
You could rebuild a pair of wheels to go on this bike at either 584 or 590 and the difference will be imperceptible. You are also extremely unlikely to have any problems with brake reach. After all, this is a diameter measure so the actual difference for brake reach from 587 to 590 is only 1.5mm. You will need to change the tyre, but you will be able to preserve the bike.
So if you are looking to repair some old wheels for your bike, these are the options open to you for rim choice. If you are looking to build a completely new set most of these sizes would be run on a traditional single speed or internally geared hubs. For hub gears I would encourage the use of Sturmey Archer, they have a huge range of geared hubs including those with freehubs, a geared fixed hubs, hubs with drum brakes, coaster brakes and kick back shifting. Sturmey Archer have also recently launched a new range of shifters. One thumb shifter and one bar end shifter. These are a great upgrade on their predecessors, improvements have been made aesthetically but also in their performance. I can also offer compatibility on unusual axle spacing for traditional road bikes.
There is a lot more information available about choosing wheelsets, building wheels and selecting component parts as well as information on repairing wheels in Bicycle Wheelbuilding: The Manual an ebook which is available to purchase exclusively here: