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The Schlumpf Mountain-Drive takes an existing drivetrain and multiplies its gear range by 2.5 on the low-end. This makes a 60-tooth (60T) chainring feel like a 24-tooth (24T) chainring.
It gives you much lower gearing for the ultimate hill-climbing, tractor-pulling granny gear.
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 Mountain Drive is with a conventional 130bcd spider which accepts most standard road chainrings, though 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 this or any other Schlumpf drive. At AlphaBENT, we've been installing Schlumpf drives since they were ever invented and we are experts at this process.
One thing to be aware of with the Schlumpf Mountain-Speed Drive is that it changes the gearing by so much that you will probably have to simultaneously shift many other gears on another gearing system you have, just to maintain some continuity when you engage or disengage the MountainDrive