I'm restoring/updating an 1970 Fresh Tandem that has a 26" wheel (700D x 1.40) and I'm thinking about swapping the wheel set with something a little more modern and accessible like a 27.5" 650B because the frame clears it, provides a little more ride comfort and it looks nice on the bike. However, I'm a little concerned about the weight limit, we're a 300 pound team (135kg) and the bike weighs around 40 pounds. Am I making a mistake here? Here's a quick photo with both wheels on for testing. The old rims are 50 years old, the tires are extreemly difficult to find and I'm planning on swapping the freewheel with a 9-speed cassette anyway.

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    It's not so much an issue of that size wheel as it is that particular wheel, with a substantially lower spoke count, and a rim of unknown (to me) strength, and probably a bit on the narrow side. May 23, 2020 at 17:18
  • Just as an aside, this is the first time I've ever heard of a bike equipped with 700D rims. I'm surprised you can find tires at all!
    – Adam Rice
    May 24, 2020 at 20:43

1 Answer 1


The rim size is immaterial to the strength of the set you choose.

Many rim brake 650b rims out there would not make good tandem rims, but there are exceptions. The VO Voyager or Diagonale in 36h are the main ones I can think of. Sun CR-18s are another, cheaper possibility. Also Velocity Cliffhanger or Atlas.

650b is likely the right choice for a conversion. If you happen to be maxing out your brake reach at present that could be a curveball, but at a radius difference of 1.5mm it's probably fine.

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    Sheldon Brown claims 700d is actually ISO 583 (rather than the earlier claim of 587), so the radius difference is only 0.5 mm from 650b/ISO 584. Might be able to just put 650b tires on the existing rims. sheldonbrown.com/harris/tires/587.html
    – Andrew
    May 24, 2020 at 2:42
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    @Andrew That's interesting to see. If it's true, whether or not a 584 would work is still going to depend on where the tolerances are landing on the rim and tire I feel. May 24, 2020 at 3:15

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