As early as the 3rd century BC, the first use of a chain drive was described by the Greek engineer, Phylon of Byzantium. As part of the polybus, a repeating crossbow, it didn’t transmit power continuously, yet it remains the first historical record of such a mechanism and the most complex. A continuous and endless power transmitting chain was used in China in the 12th century to operate an astronomical clock tower powered by a water wheel that acted as a large gear. But it wasn’t until the 16th century that the inclusion of the chain drive appears in the operation of a human-powered vehicle.
From sketches by Leonardo da Vinci, industrial designers and inventors had access to an early depiction of a vehicle where a roller chain transferred power from pedals to a drive wheel.
Propelling a two-wheeled vehicle forward, this simple mechanism was employed in early bicycle designs during the 19th century. But only when Hans Renold invented the bush roller chain in 1880, was there a great advance on the common pin-and-link chains of the day. A Swiss/British industrialist and inventor (who introduced scientific management to England), Renold is recognized for inventing the foundational design of modern precision roller chains found in bicycles today. Considered the most effective means of transmitting power devised for cycling, the roller chain remains the preferred choice for both utility and performance road cycling.
The exceptional efficiency of the roller chain, rated at 98.4% by the National Physical Laboratory, is primarily due to the reduced friction when the roller piece of the chain engages with and leaves the tooth on a sprocket (toothed-wheel or gear). Consisting of a series of short, cylindrical rollers held together by side links, the inner links (or plates) are pressed over bushings, with the rollers on the outside and the pins of the outer plates on the inside. As reliable and efficient as the roller chain was for utility, fixed wheel, and track racing cycles, it lacked the lateral flexibility needed for the derailleur gearing first developed in France in the 1930’s. Used with five or more sprockets, the derailleur chains developed in the 1980’s are of the ‘bushless’ pattern. The inner plate bushings were discarded in favor of inner plates stamped with two short tubular protrusions on their inner faces. Outer plate pins pass through the protrusions while the rollers bear against them. This improved flexibility, shifting, strength and durability.
Recent innovations in the roller chain include asymmetrical designs that improve shifting performance while decreasing weight. This new configuration is designed to cope with the weight differences on the two sides of the bike. One side has to accommodate the drive train, primarily the rings from the chain set, while the other side doesn’t. In contrast to the standard roller chain design, the asymmetric chain has distinctly different inner and outer sides to the plates and must be placed on the drive train going in the one correct direction. The plates on one side of the chain are shaped to better facilitate up-shifting on the cassette or between chainrings, and on the other side, the plates are designed for better down-shifting. It may also include hollow pins and perforations in both inner and outer plates.
Today, most bicycle chains are made from plain carbon or alloy steel, but some are nickel-plated to prevent rust and to increase the lubricity of the metal surface. Whether wet or dry lubrication increases efficiency and how best to lubricate a roller chain is open for debate, but there is agreement on the general rule for a long chain life: Never lubricate a dirty chain, as this pushes particles into the rollers (although cleaner/lubricant combo products are now available to mitigate this). Chains should be cleaned before lubrication and wiped dry after the lubricant has had enough time to penetrate the links. With its historical development and wide application, doesn’t this simple, efficient and elegantly designed piece of machinery deserve to be maintained as if it were a piece of fine jewelry?