This patent, filed by Christoph Muthers of 5rot in 2006, is for a parallelogram derailleur which does not have a parallelogram. The ends of the articulating cage are slightly different lengths, making the sides slightly off parallel. The upshot is that the angle of the pulley cage changes slightly as the derailleur moves across the sprockets - which is desirable because the angle of the chain also changes as it moves across the sprockets.

All very clever, but I am sure that I first saw a discussion of this back in the 1970s... Perhaps it was a dream.

• Publisher: Deutsches Patent- und Markenamt
• Inventor: Christoph Muthers
• Country: Germany
• Date: German application filed August 2006
• Derailleur brands: 5rot, Acros
• Derailleurs: 5rot