While at Quality Bicycle Product’s Frostbike show, I got a chance to ride the SRAM Hammer Schmidt crank system on a trainer. Seems pretty clever. When I first saw it in the magazines, I thought it was much more complicated than it actually is, perhaps influenced with my exposure to the Schlumpf crank system.
Without getting too technical, the chainring is either driven by the crank directly or, when a geared ring is held stationary relative to the bottom bracket shell, then the chainring is driven by gearing at a rotational speed faster than that of the crank. Â The front shift lever pulls a cable mechanism to capture the geared ring at the bottom bracket. A frame must be specifically equipped to use the Hammer Schmidt system, but the requirements are simply to have the tabs on the right face of the bottom bracket shell to mount the engagement mechanism. Â A custom builder shouldn’t have any major problem building a frame to use the system, but retro-fitting the system to an existing frame might not be practical, especially for aluminium alloy or carbon frames.
Compared to the Schlumpf system, the Hammer Schmidt seems to have less internal drag. Â The SRAM system is not suitable for fixed gear applications because the chainring will freewheel on the crank, thus any fixed gear rear wheel would act like a freewheel when combined with the Hammer Schmidt.Â
Most likely the Hammer Schmidt holds the most promise for downhill and freeride applications where the small chainring will improve ground clearance and the system’s constant chainline will work well with a wider range of rear suspensions.Â
But wouldn’t it be cool to combine this with a Rohloff? Â 28 internally geared speeds. Â Of course, the Rohloff offers its 14 gears sequentially with no overlap, whereas the Hammer Schmidt mimics a conventional double chainring crank.