The ingenious Schulmpf cranksets utilize a heel-activated, two speed planetary gearing system in the bottom bracket and spider to achieve a high and low range without multiple chainrings, front derailleur or shifter. Schlumpf cranksets are available as a Mountain Drive, Speed Drive, or High Speed Drive. The Mountain Drive uses a direct drive 1:1 ratio, and a low gear 2.5:1 ratio. The Speed Drive uses a direct drive 1:1 ratio, and an overdrive 1:1.65 ratio. The High Speed Drive has an integrated 27T ring with a 1:1 ratio and a 1:2.5 overdrive. All fit standard 68mm bottom bracket shells and all are suitable for tandems. The efficiency of the planetary gears is 95 - 97%.
The Torque Arm Mountain Drive will only work with single or double chainrings but it eliminates the need to chamfer the bottom bracket. Includes bottom bracket and spider, crankarms (170mm), crankarm bolts and shift buttons. Chainrings not included.
The Mountain Drive comes complete with bottom bracket, spider (130mm BCD), crankarms (black 170mm), crankarm bolts, shift buttons, and tube of lubricant. Chainrings not included.
For information on measuring your chainring bolt circle diameter (BCD), click on the link to our help page Here. For Schlumpf Drive installation documents and manuals click on the Schlumpf Drive resource page Here. More information can also be found on the Schlump Drive FAQ page Here.