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Demultiplier (Démultiplicateur in French)
A bell-crank-like device formerly marketed by Simplex as an accessory to bar-end shifters. It attached to the seat tube just above the bottom bracket. It served the function of a cable guide, but had two separate cables attached to it. The cables attached to a pivoting part at different radii, so the mechanical advantage was altered by this unit. This made it possible to shift reasonably well with the bar-end shifters, even though there was a stone-age Simplex derailer at the other end.
The cable from the shifter connects to point "1", acting on radius "A".
The cable to the derailer connects to point "2" acting on radius "B".
The cable travel at the upper section is increased by the ratio A/B.
Cable tension on the segment between the shifter and the demultiplier is reduced by the ratio B/A.
The Jtek ShiftMate is a similar device, used to match indexing when shift controls are mismatched with a different derailer.
Since the popularization of direct-pull cantilevers, such as Shimano's V-Brake, several companies have introduced new versions of the demultiplier, for example the Quality Bicycle Products Travel Agent ®, to permit conventional levers to work with these brakes.
Mark Bulgier Photo https://www.flickr.com/photos/61312162@N02/
