Something has been bugging me since I've been learning a bit about 650b: rim diameters. I have always believed that a 26inch bike has wheels with a diameter of 26 inches; and 29ers have 28 inch rims, but are "known" as 29ers. Exactly why I'm not sure.
Enter 650b. I have been told by people who should know that 650b rims measure 27.5 inches. So if all the above is correct, 650b rims are only half an inch smaller in diameter than 28 inch "29er" rims. Which isn't much.
So I went out into the shed to measure a couple of wheels. We have one 29er out there and a bunch of 26ers. I was a bit surprised to find that 26 inches is the OVERALL diameter, wheel + tyre, on a 26er. Rims measure 22.5 inches. On the 29er, once the overall diameter is approx. 29 inches, rims measure 25 inches.
Am I the only one surprised? For as long as I've known anything about bikes I have believed that the wheel size (by which the bike is known) is actually the rim diameter. But it seems to be the outside diameter of the tyre.
So, next question: what's the diameter of a 650b rim? Not 27.5inches, I'm guessing!
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