Join Date: Dec 2004
Location: Middle of da Mitten
Bikes: Trek 7500, RANS V-Rex, Optima Baron, Velokraft NoCom, M-5 Carbon Highracer, homebuilt recumbent
You got a link?
You can get an underdrive and an overdrive by installing a SRAM 3x9 rear hub. Since you have to get a new rear wheel built around the hub, it's not a trivial expense. You can also get a Schlumpf Speed Drive, which gives you a 65% overdrive. Schlumpf also makes a Mountain Drive, which provides underdrive. Schlumpfs are geared bottom brackets, and are shifted via a button on the BB axle. (Schlumpfs are not cheap, either.)
I think Slyway has some sort of funky system too, but I don't know if it's for sale separately.