Originally Posted by
robertorolfo
So my 1982 Lotus Unique, which is my bad weather commuter, originally came with 27inch wheels. ...
I've been reading about 650b conversions, and I was about to take the plunge, but my calculations seem to show that even the long-reach Tektros won't be long enough (the pad holders are about halfway down the slots with the 700c tires on, and according to the sources I've read I would need another 19mm to work with). That would mean another set of ridiculously long calipers, and so far I've only seen some flimsy looking "beach cruiser" types. ...
I think you have your answer. To get good braking with 650b you probably need to have the frame modified (have cantilever bosses brazed on). What's the widest 700c tire you can fit? How much wider could you go if you went to 650b? If there is a big difference, that is if you can fit 650 x 42b tires, I'd consider having the frame modified. But if you already have 700c wheels, I don't see how 650b conversion will really make sense.