Gran Sport: the revolution of the modern gearbox

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Gran Sport: the revolution of the modern gearbox


1949 - A prototype to change the history of cycling

At the Paris Exhibition, Campagnolo presented a derailleur for racing bikes that was so innovative that it became the forerunner of the modern derailleur.
The Gran Sport was the first rear derailleur to exploit the principle of the parallelogram derailleur for racing bikes, which is still used for modern rear derailleurs.
The revolution was that cyclists could now continue to pedal forwards without having to slow down or stop, whereas, with the dual-rod derailleur, they often had to pedal backwards for positioning.

The structure
It is said that to create the Gran Sport, Campagnolo bought two French Nivex derailleurs, improved their parallelogram system and used it for the first time on racing bikes.

But the first version of 1949 was never marketed: he made only ten prototypes.
Instead of the return spring, it had an ingenious two-cable system, one to pull the derailleur on the larger chainring and the other to pull it on the smaller one. Campagnolo did not use the usual adjusting screws to limit the width of the movement; the limit stops were built into the shifters, as in Nivex shifters.
French shifters made wheel removal difficult, while this prototype, turned 90 degrees from the Nivex, made it much easier the disassembly.

(1)


1950 First models on the market
The model presented in 1950 was more like the final version, which arrived, in modified form, to the Nuovo Record gearbox.

The derailleur clamp for the cable was rotatable to allow the optimum angle for it. The cable connection was put very close to the clamping screw because it risked breaking if had it been bent in the clamp.

The rear derailleur was attached to the bike only with its hook because in the 50's the most commonly used rear derailleurs were the rod ones, Cambio Corsa or Paris Roubaix, so bikes were not yet equipped with dropouts with a built-in hook for housing the rear derailleur (now standard in cycling, thanks to Campagnolo's innovation).

1950-51 - The first versions of the Gran Sport: a problem of fragility
The parallelogram consisted of two flat, parallel plates made of brass. However, these tended to bend with use due to the structure and the great forces at play inside the gearbox.
The gearbox structure was therefore fragile, and the pulleys also tended to wear quickly. In this version of the gearbox, the pulleys had a diameter of 30 mm, ball bearings and nine holes, probably present so as not to make the gearbox too heavy.
At this early stage of production, Campagnolo's greatest innovation still needed some adjustments to be perfect, but it was already impressive. In '51, the champion Hugo Koblet triumphed at the Tour de France using one of the first Grand Sport very first models.
Campagnolo produced three versions of the Gran Sport within a year.

(2)


First version - The 51-1

  • The additional screw of the rear derailleur is close to the upper pivot. That limits the sliding of the parallelogram, adjusting the inclination of the derailleur.
  • The hook for clamping to the dropout is forged, not moulded.

Second version - The 51-2
  • To achieve a simpler structure, the derailleur angle is fixed, so the adjusting screw becomes superfluous and is removed.
  • To keep costs down, the clamping hook to the frame began to be moulded and no longer forged.


Third version - The 51-3
Screws and bolts are changed, and the simpler and more convenient knurled clamping screw is replaced.

(3)


1952 - Improvements and increased strength
To solve the problems of structural fragility, Campagnolo produced the Extra model.
The changes were divided into two versions, the 52-1 and the 52-2.

The 52-1
That is the version where the biggest changes are more visible.

  • The fixing bolt is moved down and towards the centre of the derailleur. Thus the cable angle does not change as much as before when the derailleur shifts when changing gears.
  • The derailleur hanger no longer needs to be turned.
  • To make the plates more robust, they are now made of steel, rounded at the edges and have lost their parallelism. That eliminates the need for the reinforcing ribs of the 51-X models, and there are fewer deformed plates.
  • The steel return spring is reinforced, and this requires a thicker gauge and more winding (from 5 to 6 turns).
  • There are now six holes at the end of the spring to adjust the tension. In addition, the screw that limited the movement of the pulley cage has been changed so that it can be reached from the outside instead of the inside of the derailleur. And it is easier to remove.
  • The pulleys change from a 30mm diameter to a 35mm diameter with larger ball bearings.

(There is still the problem of wear. Campagnolo solved it with the start of mass production when they started using stronger materials).


The 52- 2

  • A more dome-shaped rear plate was introduced.
  • The elongated hole that housed the end of the return spring is removed. This model often has pulleys with 16 holes.

(4)


1953 - Mass production
Once it had solved the problem of the fragility of the parallelogram and found a lighter and stronger material than brass for the pulleys, Campagnolo finally began mass production of the rear derailleur that would make cycling history.

(5)


And thanks to the genius of Tullio Campagnolo, the improvements to the iconic derailleur continued.

(6)


The new plastic material of the pulleys made it possible to remove the holes in them. The cage returned to the size it had in '51 to avoid contact with the freewheel. The pivot bolts went from chrome to black, smaller, and recessed. The front plate became more convex, like the backplate from the 52-2 version (the dome shape had both structural and aesthetic advantages).

(7)

1956 - Both the lower part of the body and the outer part of the cage were modified. Thus the adjustment holes are changed from 6 to 3, and the spring is made thicker (from 5mm to 8mm).

1960 - The cable adjustment screw was eliminated, and the pulley cage set screw was countersunk into the lower part of the body.

1961 - To use the Gran Sport also with 6-speed freewheels, the spring is increased from 8 mm to 10 mm, to move the cage more towards the wheel. This detail also shows the genius of Campagnolo. In fact, more than ten years will have to pass before we have gearboxes that go up to 6 speeds!

 

 

(1) Gran Sport's description from a magazine
(2) Hugo Koblet
(3) Gran Sport '51
(4) Gran Sport '52
(5,6,7) Our gorgeous bike, equipped with '53 Grand Sport

 

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