French Patent # 848,964 - Idéal

French Patent 848,964 - Ideal main image

This is the second Idéal design that moves the guide pulley along a slanting path - cleverly maintaining a reasonably constant chain gap. Idéal have improved their earlier derailleur by making the sliding mechanism simpler and more robust, but have taken a step backwards by reducing the number of pulley wheels from two to one.

I was struck by the inevitable similarity of these drawings to those used by SunTour to explain its slant parallelogram design.

Browse associated derailleurs.

Ideal derailleur thumbnail

Idéal 1938