The problem the chain solved
On a high-wheeler, the pedals were attached directly to the front wheel. Every turn of the cranks turned the wheel once, so the only way to go faster for the same pedaling effort was to make the wheel larger. Wheels reached 50 inches or more, and a rider perched high above the ground paid for the speed with a real risk of falling forward.
A chain between the pedals and the rear wheel breaks that link. The pedals can turn at one speed while the wheel turns at another, set by the number of teeth on the two sprockets. That single change made it possible to use two small equal wheels, a low seat and a safer riding position without giving up speed.
Chains before bicycles
Chains were not new. Link chains were used in lifting and agricultural machinery for centuries before bicycles. Ordinary chain drives used in factories and on farm machinery were typically heavy, noisy and prone to wear. A bicycle chain needed to be light, flexible and efficient, because rider power is small compared with an engine, and wasted energy is felt.
Early experiments
Several chain-driven bicycles were built before the safety bicycle became a commercial success. French makers experimented with chain drive around 1869-1870, and in Britain a number of designs appeared in the 1870s. H. J. Lawson’s Bicyclette, around 1879, used a chain to the rear wheel and is often mentioned in this context. These machines were not widely adopted, partly because the chains of the time wore out quickly and stretched, and partly because buyers were used to the high-wheeler.
Which design was truly the first chain-driven bicycle is disputed, and the answer depends on how “bicycle” and “chain-driven” are defined. It seems fair to say that chain drive was tried by several people and that none of the earliest versions became a lasting success.
The roller chain
The practical breakthrough was the roller chain. In a plain link chain, the pins slide directly inside the plates, and the teeth of the sprocket rub the link surfaces. Wear is rapid and friction is high. A roller chain puts a small cylinder, or roller, around each pin, so the teeth roll against the roller instead of sliding. Friction and wear fall sharply.
Hans Renold, a Swiss-born engineer working in Manchester, patented a bush roller chain in 1880. His business made chains for industrial use, and the design was soon applied to cycles. It is often treated as the model for the bicycle chain that followed. As with many inventions, similar ideas had been explored by others, so Renold’s name is attached to a refined and successful design rather than to a sudden invention.
Better steel helped. The widespread availability of inexpensive steel after the Bessemer process meant that precisely made chain parts could be made in quantity and hardened to resist wear.
The Rover and the new bicycle
In 1885, John Kemp Starley’s firm introduced the Rover safety bicycle, which combined two equal-sized wheels with a rear chain drive. It has long been treated as the key design of the period. Chain drive was not the only reason it succeeded, but it was necessary. Without a chain that could survive daily use, a rear-wheel-driven design would have been a novelty rather than a replacement.
Gearing without a giant wheel
A chain makes it possible to choose a gear ratio. If the front sprocket has twice as many teeth as the rear sprocket, the wheel turns twice for each turn of the pedals. On a wheel of about 28 inches, that behaves like a wheel twice as big, or about 56 inches. That is comparable to a mid-sized high-wheeler’s front wheel, without the height. Later developments such as hub gears, chainrings and derailleurs all depend on the chain as the flexible link that makes different ratios practical.
Guards, cases and maintenance
The chain was not entirely trouble free. An open chain can catch clothing and collect dirt. Makers added chain guards, which are metal or plastic covers over the chain and sprockets, and full chain cases, which enclose the entire drive. These were especially popular on bicycles used by people in long skirts or ordinary clothing, and they remain common on city bicycles in some countries. Chain oil, adjustable rear axles and later tensioning devices became part of routine care.
Some bicycles tried alternatives, including shaft drive, in which a rotating rod and bevel gears replace the chain. Shaft-drive bicycles appeared in the 1890s and found a small market, but they were heavier and less efficient. Belt drives have also reappeared in recent years. The chain has remained the usual choice largely because it is light, cheap and easy to repair.
A quiet success
The roller chain is easy to overlook because it is so ordinary. It nonetheless reflects a common pattern in technology: a general machine element is adapted to a specific need through better materials, tolerances and manufacturing. Its history on the bicycle is that of an old idea becoming practical when metalworking caught up.