A Hungarian company called Skyex has invented the StringBike -- a bicycle that uses wires and pulleys instead of a chain. Here's how it works:
The “Stringbike” uses two steel cables attached to pulleys, which move on swinging kidney-shaped discs as you pedal. The discs replace a traditional round gear system, and you can install different discs depending on your needs, according to the Web site Hungarian Ambiance.
The position of the pedals determines the position of the discs, so that they swing in opposition — one is always pulling the bike forward, and the other lags behind. This allows a continuous transmission change, which could help a rider navigate winding streets, because you can more easily control the transmission without having to shift gears.
At the link, you can watch a video demonstrating the technology in slow motion.
http://www.popsci.com/gadgets/article/2010-09/new-chainless-bike-uses-pulley-system-eliminating-grease-and-increasing-cool-factor | Product Site | Photo: Hungarian Ambiance
Even if this is a great idea it's going to take a lot of refinement before it gets to be as good as a chain drive.
What I do not understand is why they kept on to circular pedal motion, while a linear movement of the pedals would have done the trck even better and at the same time would have made the mechanics far simpler and cheaper.
Especially on a bicycle on a sluschy winter day...