An intermediate size between 700C and mountain bike 26" makes a lot of sense from a frame geometry standpoint in the real world. Now, the traditional sizes of 650A and 650B are in fact just a few millimeters different - close enough that it's almost impossible to design a bike that couldn't use either, but just far enough apart that each requires their own unique bead seat diameter rims.
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Best,
tcs
tcs,
Thanks for the 650A education. Looking at Sheldon Brown's site, he has a lot of info on tire sizes and wheels, and Harris Cycles sells tires and rims in the 650A size.
I was going to convert a road bike to 650B to put larger, softer tires on it but now I'm rethinking this project. I may be better off with 650A rims and the more easily available 26 1 3/8" tires available for $10 at any Walmart! I'm not interested in '650B' to be snooty or cool (or French), but to build a commuter/gravel road bike that can take fenders using an old road frame.
One question: 650B is smaller than 650A by 3mm and may allow a wider tire to fit into an old 700C sport bike frame. How wide are these 650A Bell tires, and what radius is the widest part of the tire from the axle? Then I can measure the frame I'm looking at to see if these 650A wheels/tires will fit. For now I'm assuming that the widest point on the tires is about 323mm from the axle, as I have read that the widest point on a 650B tire is at 320mm. I don't have any 650A or B wheels to trial fit, so I'm taking measurments and then ordering rims and spokes through a local bike shop.
(IMHO it also looks like 650A might look better under fenders, as I think many 650B conversions with fenders look to have the fenders riding way too high.)