ABSTRACT
The link between transmission and braking lies in motion; the former transmitting the effort of the rider into forward progress, the latter in arresting it. In its simplest form, bicycle transmission has remained largely unchanged for over a century. Central to the transmission is the bottom bracket which comprises a bottom bracket axle mounted in ball bearings and free to rotate within the bottom bracket shell. A single gear chain transmission is over 95% efficient and this is a prime consideration as the power available is limited to that supplied by the rider. The advent of the mountain bike in the 1980s provided more impetus into the development of derailleur gears as the new sport of off-road cycling demanded much lower gears than were hitherto normally available. With modern derailleur systems becoming increasingly precise in operation, manufacturers have been able to increase the number of sprockets at the rear as well as using large sprocket tooth count differences where appropriate.
