Even though I like my 2009 Dahon Mu Uno a lot, I can never just leave well enough alone.. the original platform is minimalist and highly functional.. single speed, coaster brake, no cables at all to the rear.. horizontal drop outs, narrower rear spacing than most Dahons at 120mm .. the bike is stiff, folds easily, folds narrow and rolls when folded if you want, as the rear wheels are almost parallel to each other when the magnets clamp down.. stock, the gearing is about 65".. this covers a surprising amount of territory..
So what options are out there if someone wants to tweak the drivetrain, while maintaining the integrity of the original platform .. a Schlumpf drive would work, but the 1.65:1 overdrive is a pretty large step (as seen on the 2 speed Stridas). Moulton have a new model (the 50) with a Sachs Duomatic kickback 2speed + a Schlumpf Speed Drive .. after working out the ratios and how I would need to shift to get them, I passed on that thought and was considering just the Duomatic.. after finding that Sachs produced a somewhat rare Automatic Duomatic with coaster brake, and that I could get a NOS unit from a German supplier, I decided that was the route I would try.. since the Automatics are NOS with really old grease from the 60's, the supplier insists that they should be disassembled, cleaned of old grease, and re-lubed.. so that's what I did.. since I like 451 wheels more than 406 on un-suspended bikes, I laced the Automatic into an ALEX R390 451.. and laced up a matching wheel for the front.
How's it work in practice? Well, in a word, terrific! .. the Automatic has the same 1.36:1 ratio as the kickback Duomatic, so I have a 54" low and a 74" high.. pretty much perfect.. I get up the hills that I couldn't with the stock Uno and my comfortable cruising speed is up a few mphs.. 100rpm gets me around 21mph.. the hub shifts by centrifugal force.. the shift point is adjustable by varying spring tension inside the hub .. as stock it shifted at around 8 to 9 mph.. too low for my project.. I changed the shift point to just over 13mph (at around 80 rpm cadence).. this works out great.. the shift up is positive and fast .. the harder you pedal, the faster the shift.. if you have pressure on the pedals and are below the shift point (as in standing going uphill) the Automatic will not downshift until you release the pressure.. I can't believe how good this hub is.. I hope it lasts a long time.. here's a couple of shots.