One ratio was not enough
A fixed gear is a compromise. A ratio that suits flat roads feels too hard on a hill, and one that suits a hill feels too low on a flat road. For a young rider on a smooth track this may not matter much, but for everyone else it limits where the bicycle is comfortable. The history of bicycle gearing is the story of adding choice without adding too much weight or complexity.
Early attempts
Gearing had been tried on the high-wheeler in the 1870s and 1880s. Some makers built front wheels with an internal gear that increased the speed of the wheel relative to the pedals. Designs of this kind were complicated and not widely adopted, and the arrival of the chain-driven safety bicycle offered a simpler route to gearing.
On safety bicycles, an early method was to swap the sprocket or chainring, which meant stopping and using tools. Some riders fitted two sprockets on opposite sides of a rear hub, so that flipping the wheel around changed the gear. This “flip-flop” arrangement stayed in use for some time and is remembered today in the double-sided fixed hubs found on certain track bicycles.
Hub gears
The first widely successful answer was the hub gear, which places a gearbox inside the rear hub. The common type uses an epicyclic, or planetary, gear train, in which small gear wheels orbit a central gear. The principle is much older than bicycles, and gear trains of this kind are known from devices as ancient as the Antikythera mechanism, though the details are very different. Bicycle makers adopted it because it fits inside a small space and is protected from dirt.
The best-known early example is the Sturmey-Archer three-speed hub, developed in Britain in the early 1900s. William Reilly is generally credited with the design, and the names Henry Sturmey and James Archer are attached to the company. Production began around 1902-1903, and the hub spread widely on roadsters, especially in Britain and in countries that bought British bicycles. A lever on the handlebar, connected by a short rod or cable, selected low, middle or high.
Hub gears have advantages: the gearing is enclosed, shifting is possible while the bicycle is stationary, and the chain stays in a straight line. The disadvantages are extra weight and some friction in the mechanism. They remained popular on city bicycles through the twentieth century and have continued, with hubs offering five, seven or even more gears.
The derailleur
The competing approach moves the chain itself. A derailleur is a mechanism that pushes the chain sideways from one sprocket to another on the rear wheel. Because the chain can reach several sprockets of different sizes, a bicycle with a derailleur can offer many ratios.
Derailleur ideas appeared in the early twentieth century in France, Italy and elsewhere. One influential figure was Paul de Vivie, a French cycling promoter who wrote under the name “Vélocio” and encouraged touring riders to use gears for mountain roads. Early systems often required the rider to stop pedaling and sometimes to move the chain by hand or to reverse the rear wheel.
Competitive cycling was slow to accept derailleurs. The Tour de France, first held in 1903, did not allow them for many years, partly out of a belief that gears were for the less hardy. They were permitted in 1937, and from then on they spread rapidly. Tullio Campagnolo, an Italian racer and manufacturer, introduced a series of innovations, including the quick-release wheel and, after the Second World War, parallelogram derailleurs of the type that remain familiar.
Why derailleurs took over road racing
Derailleurs are light and cheap to build, and they offer many gears. The parallelogram type, with two pivoting arms, keeps the chain tensioned as it moves between sprockets of different sizes. Over the mid to late twentieth century the number of rear sprockets rose from two or three to five, six and, in later decades, ten, eleven or twelve. The cost was exposure: the chain, sprockets and derailleur are open to dirt and weather, and the system needs regular adjustment.
A divided field
The result was a split that still exists. Hub gears suited riders who wanted low maintenance and protection from the weather, such as commuters. Derailleurs suited riders who wanted lightness and a wide range, such as racers and tourers. Many cities with flat terrain stayed loyal to hub gears for ordinary use.
The same split appears in other machines. Early automobiles also faced the question of how to change ratios without losing power, and various gearbox designs competed, though the details differ. Even mechanical clocks include gear trains that convert a slow motion into a faster one. In each case, the engineering question is the same: how to match a power source to a variety of tasks.
Modern developments
Recent history has added electric shifting and new hub designs. Some electric bicycles use gearing integrated with the motor, while others let the motor do part of the work of climbing. Conventional gearing remains common, though, because it is simple, lightweight and well understood. The decades-long competition between hub and derailleur designs has not produced a single winner, because the needs of riders differ.