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  • that looks cool, but I was thinking more friction shift than be continually grumbling with indexing - this person has made it work with XTR rapidfire, but it doesn't seem that well indexed (sounds like it would skip under load tbh...)­XTM

  • I've done the 3 speed conversion with the DT swiss shifter on a 2019 Brompton. I wanted more range on the gearing, not just 3 gears, I went to 12 - 15 - 19t.

    I just found shimano sprockets which looked right and tried them. I didn't know what I was doing really and could find any info on it. I believe 17t is the spec limit but several people said you can go to 19t with barely any frame rub, possibly 21t if you're prepared to file a mm or two off the frame. I wasn't.

    The only surprises were that I needed a thinner circlip and a spacer for the chain tensioner to stop it rubbing.

    The shifting is pretty good actually. I got the DT swiss shifter expecting I may have to switch to friction, but it's fine. Just get an inline chain tensioner.

    Weirdly the drivetrain is noisy in the mid and high gears. I thought initially it was poor chain alignment, but they should be better aligned than the low gear? Maybe I have the wrong chain length? Maybe the chain tensioner is compromised for this gear range?

    There's a thread on this that no one uses BTW:­23/

    Sprockets I used:
    12t: Shimano CS-5800 Sprocket 12T for 11-28T/11-32T with Built-In Spacer (Design 12T)


    I guess I reused the 15 or 16t one that came with the Brompton.


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