I agree completely about weight, less is better and makes for a more fun riding experience especially if you want to ride without assist. If you are up to a DIY project you can get a mid 40# bike pretty easily. I was only testing Tongsheng TSDZ2 on the Dahon Jack before installing it on my wife's Dahon Briza so ignore the sloppy wiring. Total wt including 36v 540wh battery was around #45 on either bike. The Jack is a nice riding 26" folder even though the large frame is still a bit small. Installation was simple and fast as long as you know how to remove the old crank/axle assembly which is not difficult. PedalUma has suggested that it performs better without the wheel speed sensor (I need to give that a try), which makes an easy installation even easier. I've run ebike kits on several bikes with only cantilever rim brakes on steep hills, speeds up to around 40mph down long hills and on wet roads without any problem YMMV.
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Here is the Tongsheng on my wife's Briza before I tidied things up (installation on the Briza was not simple because of the unique frame)
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Here is a rear geared hub motor on my old Schwinn Sierra weighs 55# as shown (has a larger 48v 720wh battery than the Tongsheng). I've removed the controller bag because it got too hot, moved it to under the rear rack which also improved the wire routing but this is temporary also as I bought it to put on a cruiser tandem this spring.. Brakes work well on all three bikes
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