Most multi-speed bicycles rely on an elegantly simple and super-light device called a front derailleur that shifts the chain across the different size chainrings to provide a wide range of gearing. The primary disadvantage of this system is a different chainline for each chainring, which can result in dropped chains, chain suck and sloppy shifting. The need for several size chainrings can also cause clearance and suspension issues on certain mountain bikes. Recently, component maker TruVativ leaked news of its HammerSchmidt transmission, a crankset that solves all these issues by providing 2 gears from a single chainring crank that works with internal planetary gears, which is similar to how 3-speed hubs work. There's an excellent report on this ingenious new transmission, complete with videos, here. However, TruVativ isn't the first to invent something like this. There were front transmissions dating back to the turn of the century, and there's at least one other modern one, made by Schlumpf Innovations. Designed to work on road and mountain bikes, Schlumpf's Speed-Drive and Mountain-Drive have a clever shifting technique: you tap the crankarm cap with your heel to shift gears! Learn more on this cool crank here.
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