The F1-trained engineers at William Advanced Engineering assisted with the electrical parts and the result is a 250W motor that provides pedal assistance via the front hub – which is a highly unusual approach –  drawing power from a 300Wh battery pack that sits in a bag and goes on the front where the Brompton luggage rack would normally sit. You can also opt for a larger bag that holds both the battery and your spare suit or laptop or whatever. 
The environmental effects involved in recharging the batteries can of course be reduced. The small size of the battery pack on an e-bike, relative to the larger pack used in an electric car, makes them very good candidates for charging via solar power or other renewable energy resources. Sanyo capitalized on this benefit when it set up "solar parking lots", in which e-bike riders can charge their vehicles while parked under photovoltaic panels.[66]
Sometimes space comes at the most premium of commodities and the Tern Vektron offers a space-saving folding option. At about $3,400, the sturdy folding joints include a magnet and rubber strap to keep the bike folded. The quick-release pedals (wheels release too) help with storage of a bike that doesn’t give up power with a 20-mph speed that can range over 60 miles. But the best part is placing two in the trunk of a car.
E-bikes mostly use motors and battery options from a few major suppliers: Bosch, Yamaha, Shimano, and Brose. A few other brands exist, but are less reliable or powerful. Some, like the Yamaha system, have more torque and others are quieter. But generally all four make good options. Look for motor output (in watts) which will give you an idea of total power. But watt hours (Wh) is perhaps a better figure to use—it takes into account battery output and life to give a truer reflection of power.
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