This patent covers Simplex’s signature bell-crank system, used in many of their touring derailleurs for a number of decades. The key feature of this system was that it was top-normal, with the rider doing the hard work of pushing the chain ‘uphill’ from the smaller cogs to the larger ones, and the spring doing the easier work of pushing the chain ‘downhill’ from the larger cogs to the smaller ones.

The derailleur shown is the three-speed Simplex Tour de France 34.

• Publisher: L’Institut national de la propriété industrielle
• Inventor: Lucien Juy
• Country: France
• Date: French application September 1933
• Derailleur brands: Simplex
• Derailleurs: Simplex Tour de France 34