Buying Green; September 2008; Scientific American Earth 3.0; by Staff Editor; 3 Page(s)

Commuting to work by bicycle is enticing. Not only is the practice environmentally sound, it¿s healthy exercise and saves on gasoline and public-transit fares. But unless your office has a shower, showing up as a sweaty mess can make a cycling commute problematic. That¿s why the relatively new product category of electric-assist bicycles makes a lot of sense, especially if you face hilly terrain; batteries add a little power boost to each pedal stroke, making the entire trip easier.

Giant's Twist Freedom DX urban cruiser is a notable addition to themarket. The DX incorporates a battery-powered electric motor in the front wheel hub that almost seamlessly supplements your leg muscles to ¿smooth out¿ your ride. The Taiwanese company¿s Hybrid Cycling Technology is based on a torque sensor in the pedal crank that gauges how much pressure the rider exerts with each stroke. Software algorithms in the DX¿s computer take these force data and convert them on the fly into synchronized power-transmission commands for the quiet motor. The goal is to help you maintain nearly steady (and easy) exertion no matter what road you decide to take. Power is provided by a pair of four-pound lithium-ion battery packs that lock in neatly over the rear wheel. A full recharge via a standard home electrical outlet takes a maximum of six hours.