A Schlumpf Drive is a two-speed planetary gear assembly for use on bicycles. It is distinct from other bicycle planetary gear assemblies in that it is located behind the chainring rather than in the rear hub. A push-button on each side of the axle allows the rider to switch between high and low ratios. These are operated by the rider's heel.
Schlumpf Drives are primarily used as an alternative to multiple chainrings. Four models are currently produced, with differing ratios from pedal revolutions to chainwheel revolutions.
- Speed Drive, this allows a 65% increase in the final drive (ratio 1.65).
- High Speed Drive, this allows a 150% increase in the final drive (ratio 2.5).
- Mountain Drive, this allows a 60% reduction in the final drive (ratio 0.4).
- Reha Drive, this also allows a 60% reduction in the final drive (ratio 0.4). However, it is specifically designed for hand-cranked disability vehicles and requires less pressure for shifting.
Schlumpf products were initially designed and manufactured in Switzerland. They are now manufactured in Germany by Haberstock Mobility.
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