Planetary Gear Crankset
The Schlumpf High Speed Drive is a planetary geared crankset spider that acts like two chainrings on the front of your bike. In low gear, it uses a 1:1 ratio and gives you 27T granny-gear. In high speed mode, its 1:2.5 conversion ration boosts the effective gear size up to a theoretical 67.5T chainring size.
With a 20" rear wheel using an 11-34T cassette, you can expect a gear range of approximately 15-115 gear inches, with almost no overlap.
Although the standard HighSpeedDrive comes with an integral hardened steel 27T chainring and outer chainguard, it can also be ordered with a 130bcd bolt pattern to add the 130pcd chainring of your choice.
The Schlumpf High-Speed Drive yields the simplest, most effective wide-range gearing for a small wheel cycles we know of. The 130bcd version can be used for large wheel electrice cycle conversions where higher-than-normal gearing is desired.
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