• I can see how the JUY 51 works, but I don't see why it's an advantage to use the pull of the cable to keep the chain in tension rather than just winding up the spring a bit tighter. It's a similar idea to the twin lever Huret, but that allows the rider a choice as to how tight he wants the chain to be.

    What strikes me is the way that theories come and go. I've never heard anyone worrying that their chain tension is too tight and causing excessive friction, or that its slackness caused the chain to come off - the idea is completely dead. And yet most fixed/SS enthusiasts will say that their bike seems to run freer than a derailleur machine, which surely suggests there could be something in this vintage idea.