Schlumpf HighSpeed-Drive internally geared cranksets, Schlumpf installation

The Schlumpf HighSpeed-Drive takes an existing drivetrain and multiplies its gear range by 2.5. This makes a 27-tooth (27T) chainring feel like a 67.5-tooth (67.5T) chainring [if only such a device existed.]

It gives you much higher gearing for much 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 HighSpeed Drive is with a specialized 27-tooth (27T) hardened steel chainring with integrated trouser guard, 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 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 High-Speed Drive is that it gears up by so much that you will probably have to simultaneously gear down on whatever other gearing system you have, just to maintain some continuity.

For example, if you use a simple 9-speed cassette and derailleur, your lowest gear is 1 with no HighSpeed Drive engaged. The tipping point happens when you get to gear 9 and have to move into gear 10. The gearing is almost a perfect natural next step, but to do it, you have to shift all the way back down to 1 and engage the Schlumpf HighSpeed-Drive -- all at the same time. Also, if you spend most of you time at high speeds, you will be engaging the Drive's planetary gears most of the time and there will be some corresponding losses of efficiency.