Bicycle front and rear gear systems have been covered in an associated article, this article covers the transmissions that link them.
Chain Drive
This has long been the dominant transmission type. All bicycle chains have a half inch pitch, that is the distance between the chain link rivet centres, but they and their sprockets have different widths according to purpose. The width of wider chains is measured as that of the rollers between the link side plates.
On hub gear and single speed bikes that width is 1/8″, called One Eighth Chain.
On trade and heavy duty single speed and hub gear bikes, 5/16″.
Derailleur gears use narrower chains to keep their sprocket clusters narrow and facilitate the necessary slight lateral bending for changing gear, but the widths vary according to the number of rear cluster sprockets and sometimes the maker.
3 to 8 sprocket clusters use 3/32″ chain, names vary but any number 5 to 8 fits all.
Rear sprocket clusters over eight in number are measured differently. Since their sprockets are so close the overall width of the chain rivets is used, and an overall width is also given for 8 speed chains. It’s best to name the chain by its width and maker where necessary when buying replacements. Here are those details:
3-8 speed – 7.2mm (all brands)
9 speed – 6.8mm (all brands)
10 speed – 6.2mm (Shimano)
10 speed (narrow) – 5.9mm (Campagnolo)
11 speed – 5.5mm (Campagnolo)
The advantages of chain drive are the highest possible efficiency, having any gear system option and widespread availability. The disadvantages are the need for regular maintenance, they can be noisy, higher wear with narrow 9 to 11 speed derailleur chains and shorter life than other drive options. The wear is much higher when used with crank drive motors, especially as the chosen derailleur chain gets narrower.
Toothed Belt Drive
Some innovative bikes like the Strida folder have used these for a long time, but they are now increasingly entering the mainstream for their advantages. They have an efficiency disadvantage due to their non-stretch bracing inner cords requiring rubber on the inner and outer faces to compress or stretch when going around toothed pulleys. More recently thinner belts such as the Gates Carbon belt have minimised any inefficiency and they are now an attractive alternative to chains. Their advantages are no maintenance, quiet running, long life and usually lighter weight. The newer toothed pulleys can be open web types which allow snow, mud or the like to pass though without clogging, and/or have one side or centre guide for the same purpose.
Disadvantages compared to chains: They cannot be taken apart so almost all bikes’ rear frame designs must separate to allow belts to be installed. The range of lengths is limited so bikes also have to be designed to suit a specific belt size. The front and rear pulley correct alignment is critical for good belt life. They cannot be used with derailleurs. Earlier solid pulleys with two sidewall guides could clog debris between the belt and pulley.
Shaft Drive
At the time of writing the Sussex Shaft Drive bikes from Dynamic Bicycles are about to enter the UK and are already in Australia and the USA. These use enclosed bevel gears and a shaft driving a Shimano 8 speed hub gear. A previous and almost identical design which used the Shimano 7 speed hub gear and sold by Zero Bicycles was pleasant to ride. On the Zero design the shaft also acted as the bicycle frame chainstay, but the Sussex design is not frame load bearing, the bikes having a separate right chainstay.
The advantages are cleanliness and minimal maintenance with unfussy and neat external appearance. The disadvantages are no choice of gear systems and limited choice of bikes, and for e-bikes, only front hub or friction roller motors can be used.
Electrical Transmission
Only in concept and prototype forms at present, this may appear in bikes and also e-bikes. These consist of a bottom bracket generator operated by the pedals and feeding its output to a rear hub motor, thus doing away with a mechanical drive from front to rear. That forms a normal bicycle powered only by the rider. In an e-bike variant, the rear hub motor could be optionally driven solely by the rider output, solely by the e-bike’s battery, or by any combination of the two electrical sources, a true hybrid.
The disadvantage is marked inefficiency due to two energy conversion stages, but in some applications that could be acceptable for the application advantage. An example is compact folding bicycles where a mechanical drive like chain or belt compromises the fold possibilities in a way that an electrical cable doesn’t.
Which transmission to choose
This depends on one’s priorities. For maximum efficiency, performance and widest range of gear choices it’s chain drive. For zero maintenance and cleanliness with hub gears or single speed it’s the belt drive. For cleanliness and neatness of appearance with low maintenance it’s worth investigating available shaft drive options.
Our thanks to Flecc for this article. Flecc is a long-time contributor to Pedelecs. If you have a question you’d like Flecc to answer please contact us here.
