“..the satanic but nonetheless fabled Campy Cambio Corsa shifter..”
(Sheldon Brown)
There are two levers in the Campagnolo Cambio Corsa rod shifter. The top (longer) lever is the rear axle quick-release. The bottom (smaller) lever is the gear changer with the side plates of the derailing fork pushing the chain across the four available cogs. Unlocking the quick-release allows the rear axle to roll forwards and backwards in the notched horizontal dropout. The notches are on the underside of the top surface of the rear dropout and engage matching teeth on the rear axle. The rear axle rolls in relation to the notched underside of the top surface of the dropout but slides/ slips in relation to the dropout’s smooth bottom surface.
When the axle is unlocked the rear wheel is, effectively, disconnected from the rest of the bicycle and its rider. On a flat surface, at a constant velocity, for a brief moment before friction and momentum changes the situation, the rear wheel is also travelling at the same speed as the rest of the bike. If the chain is also de-tensioned by back-pedalling then a shift can be effectuated by smoothly manhandling the chain across the rear cogs using the supplied lever. As the derailing fork moves across the different cog diameters the rear axle accommodates the fixed chain length by rolling forwards or backwards within the dropout. So long as the chain tension is neutralised, the road surface smooth, and the gear change quick, the engagement of axle’s teeth in the notches of the dropout will keep the rear wheel square with the frame.
The rear dropout is also slightly canted backwards which means that the axle of an unlocked rear wheel will naturally move backwards on the dropout as the weight of the bicycle and rider centres forward of the rear dropout. In a standard bicycle with smooth, long dropout surfaces the backward settling of an unlocked rear axle is easily overpowered by the chain tension that occurs when the rider pushes forward on the pedals. In a bicycle like the Bianchi Folgore, light forward pressure on the pedal tensions the top part of the chain (like a standard bicycle) but forces the unlocked rear wheel slightly backwards in the dropout. This occurs as the underside of the top surface of the rear dropout (which is loaded) is notched and - assuming a gentle load over a smooth, flat road - the teeth on the rear axle engages the notches on the dropout preventing slippage at this contact point. On the other hand, the top surface of the lower fork on the rear dropout is smooth (and unloaded) allowing the axle to slide/ slip as there is no direct engagement with the toothed axle. This leads to the axle rolling backwards.. in theory.. most of the time.
In summary: to change gears the rider flicks open the quick release, de-tensions the top part of the chain by back-pedalling, flicks the gear lever across the cogs, locks the quick release, then accelerates into the distance. As the paragraph above explains, there is some (tiny) leeway for error. A lightly loaded chain that occurs through forward pressure on the pedal before the the rear axle is locked settles the rear axle in the dropout and re-tensions the chain (ideally, this step should be incorporated after a shift to remove slack in the returning chain). In any case, only after the rear axle is locked can the rider pedal forward then accelerate in a linear or angular direction.
It's very clever.
Some people even make it look simple:
https://www.youtube.com/watch?v=A7rjurYxcNI
It is not.
The history of chain derailing systems for bicycles is littered with experiments and obsolete designs. The Cambio Corsa is just one of many clever inventions utilising derailing forks in preference to guide pulleys. If this sort of thing interests you then Frank Berto’s excellent book, The Dancing Chain, remains the best resource for muddling through the mess of ideas and innovations that eventually saw the Bowden-cabled, two-pulleyed, articulating parallelogram pull to the front. This densely detailed book outlines the bicycle’s progression from a rider striding on a velocipede to a cyclist pedalling a continuous chain drive and why epicyclic hub gears became popular in Britain while chain derailing systems took hold on the Continent. But the book’s main focus is the history and development of the derailleur bicycle (hence its wonderful title). We get to Campagnolo’s reliable and well-marketed “Gran Sport” about halfway in the book (halfway in the first edition, a bit earlier in subsequent editions) then travel down the path laid forward by the popularity of this type of derailing mechanism. From thereon the incremental improvements in derailleur technology can be easily cross-referenced with the amazing compendium of rear derailleurs at the Disraeli Gears website (see link below). This is an intricate history of something most cyclists take for granted. And, humbling. If you read this post and take away these two reference sources then 95% of my work is done. If you are wondering why this post even exists then I give you this:
Anyway, “back in the day”, it was a challenge to derail a continuous chain on rough road surfaces. The following is my attempt to rough out an altogether inadequate summary.
In the thirty years between 1900 and 1930 the impetus to make bicycles with multiple gears took hold but the technology to derail a continuous chain was varied and rudimentary. It was also seen by many racing cyclists (and race organisers) as unnecessary and unreliable. But the derailleur concept thrived in France largely thanks to the pioneering work of Paul de Vivie and his coterie of enthusiastic “cyclotouristes” tinkering away with their bicycles and riding up and down hills. Paul de Vivie died in 1930 but the following years bracketing the Second World War saw the variable-speed, derailleur-equipped road bicycle come of age throughout Europe (and the countries they colonised) lead by France. It’s not for nothing that serious collectors covet 1930s-1950s French bicycles like Alex Singer or Rene Herse equipped with Nivex or Cyclo Standard derailleurs (Nivex and Cyclo are French). Or that the the biggest derailleur manufacturer in the 1940s-50s (by far) was Simplex (also French).
While the French - for various reasons - saw the bicycle as a means for recreation and exploration, the rest of the world came to see the bicycle as a utilitarian vehicle for commuting (for those unable to afford motorised transport) or for racing. Because racing can be seen as a singular test of a rider’s strength, endurance and fortitude then a bicycle with one gear can be seen as an appropriate vehicle for the task. This perception persisted for decades. Years passed, the Great War came and went, and trouble started brewing again in Manchuria, Europe, and Ethiopia. In the 1930s derailing technology on a bicycle was still novel and unrefined but proved revolutionary enough to compensate for the shortcomings of the less endowed. Professional cyclists recognised this and pressure mounted on race organisers to accommodate these clever contraptions. In 1937 Henri Desgrange allowed geared bicycles in the Tour de France. There was no turning back. Two years later the world was again at war.
The biggest bicycle race was French but the focus of derailleur excitement moved from France to Italy Campagnolo. In 1933 Campagnolo brought out a rod and lever derailleur system but it was only after the Second World War that it was refined and marketed as the Cambio Corsa. The forward-looking boss of this growing company also did a good job cajoling and enticing Italian racing cyclists to use his equipment. Then two great postwar cyclists (both Italian) set the course of history. Gino Bartali won the 1948 Tour de France using the Cambio Corsa (he also won in 1938 using another Italian-made but rather inelegant, pedal-backwards-to-change-gears derailleur). The following year Fausto Coppi (not a conforming type) was lured across to Simplex and won the Tour de France using their spring-loaded, telescoping-rod rear derailleur. That the great French race was won in 1949 by Italy’s “Il Campionissimo” using a French derailleur did not go down well with Mr Campagnolo.
Not nine months later Fausto Coppi won the 1950 Paris-Roubaix using the single lever version of Campagnolo’s rod and lever derailleur (subsequently called the Campagnolo Paris-Roubaix).
Nevertheless the writing was on the wall. And Campagnolo was onto it.
https://www.bikequarterly.com/
An intriguing illustration by Daniel Rebour shows a prototype Campagnolo Gran Sport derailleur sporting a parallelogram articulation, a looped cable system, and a cage housing a guide pulley and tension pulley similar to a Nivex derailleur but rotated 90 degrees and attached to the rear dropout. It is paired with a down-tube shifter identical to the Cyclo (Bicycle Quarterly, Vol 2, No 2 and Vol 12, No 8). The drawing was printed in Le Cycle in 1949 and represented a prototype made for the 1949 Milan Bicycle Show. A year later Le Cycle had another illustration by Daniel Rebour showing the Campagnolo Gran Sport derailleur with a single Bowden cable and a return spring.
In 1951 Hugo Koblet (Swiss) won the Tour de France using an early version of the Campagnolo Gran Sport.
In 1952 Fausto Coppi won the Giro d’Italia then went on to win the Tour de France using a later version of the Campagnolo Gran Sport.
In 1953 Campagnolo released the first standard production model of its articulating parallelogram rear derailleur. That same year the Gran Sport was incorporated into the first “gruppo” or bicycle groupset which then became Campagnolo Record (1963), then Nuovo Record (1967), then Super Record (1974).
… just like the French touring derailleurs.
Chain wrap is improved at the expense of an increased gap between the guide pulley and the rear cogs. Thankfully the articulating parallelogram adds rigidity.
Outside of track cycling the world of bicycling is not smooth and flat, nor is it traversed at a steady, constant velocity. That’s why gears and gear shifters were developed for bicycles in the first place. History, practicality, trial and error, and the “path dependence” taken by rear derailleurs tell us that the Campagnolo Cambio Corsa was an interesting curiosity but the Cyclo, Nivex, Simplex Champion du Monde, Campagnolo Gran Sport, Suntour Gran-Prix, and Shimano’s SIS were great.
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