Bicycle drivetrain systems
Bicycle drivetrain systems are used to transmit power on bicycles, tricycles, quadracycles, unicycles, or other human-powered vehicles from the riders to the drive wheels. Most also include some type of a mechanism to convert speed and torque via gear ratios.
The history of bicycle drivetrain systems is closely linked to the history of the bicycle. Major changes in bicycle form have often been initiated or accompanied by advances in drivetrain systems. Several early drivetrains used straight-cut gears that meshed directly with each other outside of the hub. Some bicycles have used a double-sided rear wheel, with different-sized sprockets on each side. To change gears, the rider would stop and dismount, remove the rear wheel and reinstall it in the reverse direction. Derailleur systems were first developed in the late 19th century, but the modern cable-operated parallelogram derailleur was invented in the 1950s.
Power collection 
Bicycle drivetrain systems have been developed to collect power from riders by a variety of methods.
From legs 
- Swingbike and Risigo that moved the seat and pedals in coordination.
From arms 
From whole body 
From multiple riders 
Power transmission 
Bicycle drivetrain systems have been developed to transmit power from riders to drive wheels by a variety of methods. Most bicycle drivetrain systems incorporate a freewheel to allow coasting, but direct drive and fixed-gear systems do not. The later are sometimes also described as bicycle brake systems.
Two-wheel drive 
In 1991, a two-wheel drive bicycle was marketed under the Legacy name. It used a flexible shaft and two bevel gears to transmit torque from the rear wheel, driven by a conventional bicycle chain with derailleurs, to the front wheel. In 1994, Steve Christini and Mike Dunn introduced a two-wheel drive option. Their AWD system, aimed at mountain bikers, comprises an adapted differential that sends power to the front wheel once the rear begins to slip. In the late 1990s, 2WD 'Dual Power' mountain bikes were sold in Germany under the Subaru name. They used one belt to transfer power from the rear wheel to the head tube, a small gearbox to allow rotation of the front fork, and then a second belt to transfer power to the front wheel.
Speed and torque conversion 
A cyclist's legs produce power optimally within a narrow pedalling speed range. Gearing is optimized to use this narrow range as best as possible. Bicycle drivetrain systems have been developed to convert speed and torque by a variety of methods.
Several technologies have been developed to alter gear ratios. They can be used individually, as an external derailleur or an internal hub gear, or in combinations such as the SRAM Dual Drive, which uses a standard 8 or 9-speed cassette mounted on a three-speed internally geared hub, offering a similar gear range as a bicycle with a cassette and triple chainrings.
While several combinations of power collection, transmission, and conversion exist, not all combinations are feasible. For example, a shaft-drive is usually accompanied by a hub gear, and derailleurs are usually implemented with chain drive.
See also 
Elliptical foot motion on a modern treadle bicycle
- Frank Berto (2009). The Dancing Chain: History and Development of the Derailleur Bicycle (Third ed.). Cycle Publishing. pp. 23–28. ISBN 978-1-892495-59-4.
- "3G Stepper Bike: A Fitness Monster that Beats Your Gym Membership". Popular Mechanics. October 1, 2009. Retrieved 2010-07-13.
- "A Different Kind Of Bicycle". Gadgetopia. Retrieved 2010-05-26.
- Wallack, Roy M. (30 November 2009). "Going Beyond the Basic Bike". LA Times. Archived from the original on 28 June 2011. Retrieved 2011-05-12.
- Richard Peace (Mon 11 Jan 2010). "ElliptiGO seatless bike launched". BikeRadar.com. Archived from the original on 29 July 2010. Retrieved 2010-07-13.
- "Weird Bikes II - More Weird Bike Stuff". Charlie Kelly. Retrieved 2012-07-17. "Here we have not one but TWO examples of bikes that raise and lower the rider during each pedal stroke. On both of these bikes, the rider pedals with his feet together and stands up and sits back down to propel himself."
- "Weird Bikes II - Total Body Bikes". Charlie Kelly. Retrieved 2012-07-17. "Slide the handles in and out as you ride, with the motion transmitted to the front wheel via a system of cords and springs."
- "Weird Bike Stuff - Legacy 2 wheel drive!". Charlie Kelly. Retrieved 2012-07-17.
- "Christini background". Elan Ligfietsen. 2005. Retrieved 2012-07-17.
- Michael Embacher (2011). Cyclopedia. Fontaine & Noë / Lannoo. pp. 46–47. ISBN 978-90-72975-08-9.
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- Additional alternatives not yet notable enough for their own article