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The Schlumpf Speed-Drive takes an existing drivetrain and gears it all up by 60% when needed. This makes a 35-tooth (35T) chainring feel like a 56-tooth (56T) chainring.
It gives you higher gearing for higher speeds.
All of this happens with no shifter, no shift-cables, no shift-cable housing, and no barrel-adjusters.
Instead, you switch gears by kicking a button from side to side on your bottom-bracket spindle.
The most common conformation of a Schlumpf SpeedDrive is with a 110bcd five-arm spider, but other chainring systems are available if this just won't work for you.
The drive is held in place with 45-degree chamfered friction. This means that the bottom-bracket of your cycle needs to be specially machined and prepared in order to accept a Schlumpf drive. At AlphaBENT, we've been installing Schlumpf drives since they were ever invented and we are experts at this process.