29 January 2012

Schlumpf-Equipped Airnimal Chameleon Folding Bike

After struggling with a troublesome front derailleur on his Airnimal Chameleon folding bike, Bruce Metras of B. Metras Company (San Rafael, CA) upgraded his bike with the installation of a Schlumpf Speed Drive.

The Schlumpf system simplifies the drive train by using a single chain ring in the front that is connected to a two-speed internal gear system encased in the bottom bracket. Since the chain remains on a single ring, there is no possibility of an overshift occurring that would result in a dropped chain. This set-up also allows riders to access all available gears on the rear cassette, as the centered chain line eliminates cross-chaining.

The 1.65 ratio change of the Schlumpf SpeedDrive offers a direct gearing replacement for the original front derailleur and double crank set. For smaller-wheeled bikes, like the Airnimal, this option is especially useful, as it gives riders the same effective gear ratios available on standard bikes without requiring the use of extra-large chain rings. Often, the chain ring size needed to get the desired output is so large that it is not readily available and leads to shifting problems due to component size mismatch:
  • Front derailleurs are shaped to work with the chainrings sizes commonly found on bikes with 26" and 700c wheels. Larger rings do not match this shape well.
  • The difference in tooth count between two chain rings increases as their size grows (assuming a fixed ratio between them) and quickly exceeds the capacity of the front derailleur.
  • The chain angles created by the large chain ring and shorter chain stays of a smaller-wheeled bike cause poor shifting and excess chain and sprocket wear.
With a Speed Drive, these issues are eliminated. Riders can use a single smaller ring and still get the larger gearing that is desired without any of the problems associated with using larger chain rings on small-wheeled bikes. Riders of standard bikes also benefit from the Schlumpf set-up. Check out our previous post on using a Schlumpf Speed Drive on a fixie.

Bike highlights
  • Frame: Airnimal Chameleon folding bike
  • Front Gearing/Front Derailleur Replacement: Schlumpf SpeedDrive Gearing System
  • Crank arms: Truvativ left-side square taper arms with right-side pedal insert on one arm


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  2. I've been considering the merits of using a Schlumpf on a belt-drive bike, to get lower gears than are ordinarily obtainable with a non-Rohloff rear hub. Do you know whether or not the Schlumpf is compatible with an eccentric bottom bracket?

  3. Yes, the Schlumpf drive units are compatible with EBB's. Schlumpf also offers units with a built-in EBB insert machined to fit the ID of your EBB shell. This version requires an EBB design where the frame clamps the insert. It is not compatible with frames that use an expanding wedge style EBB (Bushnell, DaVinci, etc.).