There are some 7 speed 20" Dahon clones with mechanical disc brakes, alloy frame and steel forks for 12.5 -> 13 kg - add a 1.6 kg AKM hub motor , KT controller and 1.8 kg 36V 10Ah bag battery ( and @saneagle 's 11-32t sprocket ) they will weigh 16.5 kg to 17 kg and it is a very capable bike...