My quest to rehab a $50 1989 Dahon Getaway V and upgrade it for higher speeds is probably at an end.
As others had mentioned, the severe chain angles caused by the short chain stay length limit the rear derailler to 5 gears. While it's possible to engage more gears, the further inboard or outboard the gears, the more likely the chain will fall off the front ring.
I fitted a 6-speed with a 13 tooth cog vs the original 14, but can only use the 5 highest gears, The lowest gear caused the chain to fall off the front, so I used the derailleur limit screw to block that gear. Yesterday I put the 7-speed 11-32 from my 20" Boardwalk on it, and was able to push the gears far enough inboard so that the chain stayed on the highest gear (the 11), but
then it rubbed against the next highest gear and prevented the chain from staying on the 11 cog. So I will stay with the 6-speed for now. (A front derailleur, or rear internal hub would be better).
The bike had only a slightly adequate rear band brake when I bought it (used) and I believe it came that way as Dahon did sell many like that.. I added a font caliper which makes the bike stop fairly assuredly. I planned on replacing the rear with a caliper brake, especially in light of my anticipated higher speeds, but for now, this will work.
And as far as increasing the speed, which was my initial quest. This almost 35-year old folding frame has a fair amount of flex, although the fold seems secure. But the buttressed mast does not instill confidence, especially since the original push-button latch was absent. My brass plumbing hack seems to work well, better than some of the OEM latches I have tried, but the whole two-part steering mast also allows for some flex.
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DIY Dahon Brace Latch...SUCCESS!)
Given the frame and mast flex, the 30-lb weight, the complexity of a meaningful drive train overhaul and the need to upgrade the rear brakes, I think I am done with this project. Total cost and investment $125.
It's been a fun project, but it won't be a regular commuter choice for me. Now I'm thinking a tri-fold, or another newer 16-inch bi-fold with an internal hub and and more modern, more easily upgradable components.
