Originally Posted by
pengyou
Is there any way on a folding bike to put the rear derailler on top of the frame instead of on the bottom?
No, that wouldn't work. The chain pulls along the top of both chain ring and sprocket, and the derailleur is down below to take up the slack. If you put the derailleur up top somewhere, pedalling would take up the slack from the top and put it down below, where it would cause havoc.
Originally Posted by
pengyou
Any suggestions?
Internally geared hub.