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Chain
Modern bicycles use roller chain to connect the cranks to the rear wheel. Chain drives are among the most efficient means of power transmission known.
Chain size is specified by pitch and width. The pitch is the distance between rollers (1/2" on all modern bicycle chain). The width is nominally the width where the sprocket teeth fit in. Bicycle chain comes in four basic widths:
- 3/16" (.1875", 4.76 mm), used until the middle of the 20th century on many bicycles; this was inch-pitch chain.
- 1/8" (0.125", 3.18 mm) chain is used on most single-speed bicycles, and bicycles with internal gearing.
- 3/32" (0.094", 2.30 mm) chain is used on derailer equipped bicycles that have more than 3 cogs at the rear.
- Even somewhat narrower chain, typically .090" or 2.29 mm between the inner plates, is used for derailer-equipped bicycles with 9 or more sprockets at the rear.
There is some confusion in these numbers because the actual width of a 1/8" sprocket is typically 1/8"(3.175 mm) and the gap between the inner side plates of the chain must be slightly wider to fit over the teeth. The width of the teeth on derailer-equipped bicycles with 5 or 6 rear sprockets was traditionally 2 mm, and the 3/32" (2.30 mm) chain would fit over those teeth -- but the smaller widths with larger number of sprockets are not as well standardized. Chains for derailer applications also come in various external widths. Newer clusters which have more sprockets also use chain with thinner side plates and with rivets whose ends are flush with the side plates.
For more information on chains, see my article on Chain Maintenance.
