This rather sophisticated design shows a twin pulley touring derailleur in which the pulley cage slides along two slanted rails, in an attempt to maintain a reasonably constant chain gap. As such it anticipates some of the benefits of SunTour’s game-changing sloping parallelogram design. It certainly shares a lot with White Industries’ 1996 LMDS concept.

It is worth noting that on this French patent the inventor is listed as Claudius Jacquemard. However, in the equivalent UK Patent # 408,915 - Idéal, the inventor is listed as Giovanni Perona of Torino. Perhaps Giovanni is the original inventor and sold his design to Claudius who then marketed this design under his Idéal brand.

In 1938 Claudius developed this idea further in French Patent # 848,964, which also led to a commercial Idéal product.

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• Publisher: L’Institut national de la propriété industrielle
• Inventor: Claudius Jacquemard
• Country: France
• Date: French application September 1931
• Derailleur brands: Idéal
• Derailleurs: Idéal 3 speed