Originally Posted by
Road Fan
One reason I'm concerned is that my frame has canti posts placed for 700c rims. I'm not 100% clear on the lateral and radial clearances, but I'm pretty sure I can't fit a 650 wheel unless I do cosmetic surgery on the frame and fork to relocate the brake pivots. I'm planning to use the Berto chart to see how wide I can fit.
Our old tandem was a Trek T200 with 700c canti posts. It could*safely* fit a 700c x 32mm tire, but we sometimes used 35-37mm. We stuffed 650b x ~50mm tires into it. For the rear brake, I used a Diacompe 990 U-brake on a U-brake adapter plate. It was mounted underneath the seatstays to avoid interference with the 700c canti posts. It was a bit of a kludge, but it got the job done. For the front, we got a disc fork. We've since given that bike away (with 700c wheels and cantilever brakes), but I think I have that U-brake setup in a box somewhere. I've attached an image of the U-brake with the 700c rim still installed.
990 U-brake for 650b rim installed on Trek T200