Shaft-drive bicycles live! There are several makes on the market, all of which use the basic layout of a bevel gear that turns drive through 90 degrees at each end of a drive shaft. Claims by manufacturers that such drives can match the efficiency of a chain are implausible, since each set of bevel gears absorbs a significant amount of power. The advantages of low maintenance and cleanliness are, for most applications, outweighed by considerations of power loss, weight and complexity. They also hinder rear wheel removal and require the use of hub or singlespeed gearing, but in some purely utilitarian applications they work well.
Cycle's Technical Editor