The Johns Hopkins Gazette: August 30, 1999
When it comes to efficient use of energy, it’s tough to beat a bike. That’s what Johns Hopkins engineers learned when they aimed an infrared camera at a computer-controlled bicycle drive train in a campus lab. The camera detected heat generated by friction as the chain moved through the sprockets under varying conditions. This heat represented wasted energy, and by measuring it, the engineers were able to identify sources of inefficiency.

In the best test, the chain drive posted an energy efficiency score of 98.6 percent, meaning that less than 2 percent of the power used to turn the front sprocket was lost while being transmitted to the rear one. Even the worst test turned in a respectable 81 percent efficiency score.

Link to the whole piece.
Thanks for the link SM.