French Patent # 965,889 - Simplex

French Patent 965,889 - Simplex main image

Lucien Juy, of Simplex, and indeed many other derailleur designers, spent the 1940s and 1950s obsessing about chain tension. Today we cannot quite understand this, but we live in a world of effective derailleur geometries and strong long-lived springs. Perhaps, if our derailleurs were imprecise and our springs were weak and rapidly got weaker, we might believe in all kinds of engineering black magic.

This patent describes a mechanism by which the rider pulls the cable and this pulling of the cable cable increases the tension in the main spring in the derailleur.