3. Rear derailleur
3. Rear derailleur
Before the rear derailleur came along, there was one way to change gear. That involved getting off, removing your rear wheel, turning it round, slotting the other sprocket (because you only had two) into the chain and setting off again.
Needless to say, it made changing gear a far bigger decision than just pushing the shifter slightly to the left as we do today.
Various derailleur systems were designed in the late 1800s, most of which allowed switching between two gears using rods or, like the Campagnolo Cambio Corsa, paddles mounted on the seat stays. They were introduced into the Tour de France in 1937, and in 1949 Campagnolo released the Gran Sport, which popularised the parallelogram rear derailleur.
Since then, the introduction of indexed shifting in the 1980s by Shimano kick-started the need to have a fully compatible system of shifters, derailleurs, cassette and chainrings, and was the first promotion of what we now call groupsets.