While stumbling around around the interweb tonight I found an interesting Q&A with William Ostrem of Northern Letter and Sean Virnig of Rawland Cycles.

The part that intrigued me the most about the answers that Sean was giving was this :

Bill: My wheels [on my Surly] are 700C, I think. Why would I change to 650B?

Eric: My Baccheta recumbent is 650C.

Sean: 650B has more volume than 700C of the same size (width). You’ll feel more comfortable, the ride will feel more smooth over potholes etc (especially with Carol [Molnau] still the Commissioner of the [Minnesota] Dept. of Transportation). 650B is also beneficial for off-road tires. I don’t like the 29er because it’s too big in my opinion. It handles funny because it uses the same rim size as road bikes (700C). The 650B off-road wheel/tire has the same outside diameter as your 700C so it handles just like a road bike. Moreover, with the disc Sogn, one can swap between off-road 650B wheels and 700C road wheels without affecting handling characteristics, geometry, and so on. That’s an extreme example, but you get the idea.

One interesting story: in the early 80s before mountain bikes became popular the founding fathers of mountain bikes decided on 650B as the ideal size for mountain bikes, but [the] CCCP [the Soviet Union] bought out all 650B tires from a Finnish tire company so the fathers had to switch to 26.

Image from Northern Letter