Joined: Mar 2014
Posts: 18,274
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From: ,location, location
Bikes: Foundry Chilkoot Ti W/Ultegra Di2, Salsa Timberjack Ti, Cinelli Mash Work RandoCross Fun Time Machine, 1x9 XT Parts Hybrid, Co-Motion Cascadia, Specialized Langster, Phil Wood Apple VeloXS Frame (w/DA 7400), R+M Supercharger2 Rohloff, Habanero Ti 26
A good conversion candidate is a bike that has a motor mount for say a Bosch or Brose motor and ideally a battery mount as well or in the case of Bosch something that has the connections and space for the new PowerTube battery. Generally though in that case I would just go for the complete bike.
I wouldn't convert any bike unless it was built with tubing designed to handle high torque and extra weight. So something like a road bike for instance would be a poor choice unless it was built as an e-bike in the first place.