Schlumpf Crank Arms
Schlumpf Drive units offer planetary, two-speed, gear-driven crank/bottom bracket systems that allow you to expand the gear range of a single-speed, fixed-gear, or internal gear hub-equipped bike while maintaining a clean look.
Two gear ratios are available without the chain moving between gears, and there's no front derailleur, shifter, or cables to maintain or clutter up your bike. You simply shift with a quick heel movement against the push-button axle in the center of the crank arm. The gearing systems use a clutch plate design that won't slip under power and requires very little maintenance.
Cycle Monkey offers all three of Schlumpf's gearing systems: Speed Drive (1.65 overdrive ratio), Mountain Drive (2.5 reduction ratio), and High Speed Drive (2.5 overdrive ratio) in a wide range of configurations. We also have a longer axle version that is compatible with the 54mm chainline of the Rohloff SPEEDHUB 500/14 internal gear hub. Crank arms are available in black or silver in a variety of lengths.