This Simplex Champion de Monde Extra-Leger is an example of a design that Simplex produced in a lavish range of different variants and under a profusion of different names (Champion 35, Champion 36 and Champion de France being some possibilities) between 1935 and 1948. These derailleurs were a huge commercial success and did much to establish the derailleur as a standard piece of racing equipment. Simplex produced them in their hundreds of thousands, and marketed them by aggressively sponsoring leading riders to use them, establishing a pattern that persists to this day.
The Simplex Champion du Monde Extra-Leger was an advanced technology (for the time) aluminium version. Even the hanger plate is an aluminium casting.
None of this means that it worked very well. It was fragile, imprecise and had very limited capacity - but at 165g it was, genuinely, fantastically light.
In the photograph I have disengaged the main spring to allow the gear to take up a more normal position.
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