Knob Magazine

the underside of the derailleur reveals a unique design that may boast an auto adjustment feature.

A few weeks ago I published some images from a recent patent filing that looks to be the new FSA 11 speed derailleur.  The design was in a word: unique.  In what has been described as a rack and pinion setup, the derailleur forgoes the typical parallelogram linkage and uses a single arm with internal gearing to keep everything aligned.  Concerns over the durability and reliability of such a radically different design prompt the question “why?”.

After more detailed review of the application the answer lies in a unique auto-adjustment feature.  Unlike standard parallelogram design, where the cable attaches to a fixed point on one arm or the other, this design features a separate mechanism that rotates along the same axis of the ‘arm’ b-knuckle pivot.  With the former when the derailleur hits bottom, or normal in derailleur speak, the cable goes slack.  With the design in the application  the position of the cable anchor relative to the derailleur is variable.

The brilliance of the FSA design appears to be a ‘spooling’ mechanism that pulls the slack from the cable every time the derailleur returns to the normal position, thereby maintaining proper adjustment.  The advantages are obvious.  First, however narrower their 11-speed system might be, it is naturally less tolerant of fluctuations of cable tension than its older 8 or 9 speed counterparts.  Back then the solution to the stretch problem was to actually put play into the derailleur by means of a floating upper pulley.  As systems became more precise, this arrangement became finicky.  I assume that this design could forgo a floating pulley, making shifts more precise in the process.  As an added benefit, down-shifts would require less cable pull, reducing the amount of necessary displacement at the lever.

As I reported earlier, the design is setup for easy conversion to a electronically driven setup by use of either a rotational motor or a servo.  Indeed FSA seems prepared for such contingencies, illustrating several possible electronic setups that I anticipate may be in the works for a later generation of the system.

US Patent App. 20070216130