A Campagnolo masterpiece: the Cambio Corsa
Cambio Corsa, a masterpiece of engineering, is a dual-rod gear changing system. It was patented in 1930 by Tullio Campagnolo, the owner of the eponymous company, and inventor of the famous quick-release hub, the same mechanism the Cambio Corsa utilized.
Since its introduction in 1946, Cambio Corsa was an immediate success and became widely adopted in professional cycling.
It was a multi-gear changing system consisting of a rear-wheel quick-release lever with a mechanical extension that placed the lever itself near the bike's saddle, combined with a fork that served as a rear derailleur (without idler pulleys to take up slack), that also had a control lever near the bike saddle.
This innovation enabled bicycle riders to change gears while in motion by releasing the axle, moving the rear wheel slightly forward by applying tension to the chain, actuating the fork to change to a larger sprocket, and tightening the quick-release again. Or else releasing the axle, actuating the fork to change to a smaller sprocket, moving the wheel slightly rearward by braking, and tightening the quick-release again.
The racers could thus move the chain on the rear sprocket without having to use a tensor. In fact, the number of teeth changes by moving the chain through the derailleur. Therefore the chain must be tensioned to make a grip on the teeth and allow the force to be applied to the wheel. This is why the wheel must be able to slide back and forth. This is possible if it unhooks from the frame to move freely.
There are two types of Cambio Corsa:
Corsa, with shorter levers;
Sports, with longer levers.
HOW IT WORKS
Today the use of a dual-rod derailleur system can appear complicated. But when they were introduced the racers had specialized in making the change without stopping and for the best ones, this was their greatest strength.
1. Rotating the top lever on the outside frees the wheel from the dropout;
2. Move the lever below in the direction of the gear on which you intend to slide the chain;
3. Pedal backwards to blow the chain from the starting gear to the end manoeuvre (step 2 and step 3 must be carried out simultaneously);
4. Derailment and back-pedalling generate the wheel slippage forward (if you have switched to a larger gear) or backward (if you have switched to a smaller one). But the movement is not entirely free. In fact, the bikes with this gearbox are equipped with toothed dropouts that make the slip stop at predetermined measures and then already recorded;
5. Fit the top lever to re-attach the hub to the dropouts.
In the photos: details of a Patelli bike equipped with Cambio Corsa