document updated 14 years ago, on Oct 13, 2010
Ways to get a 20" or 24" BMX bike to have at least two gears, so I can have an extremely low gear for flatland / the skatepark, and one that's in the typical range for SS/fixie commuter bikes:
- dinglespeed — a "double singlespeed"
- main downside: it can take several minutes to "shift"
- retro-direct — you can instantly shift between two single-speeds
- main downside: it's a very experimental solution, it's not clear if it can be as reliable as a singlespeed, especially for winter commuting
- Rohloff Speedhub — from everything I've read, it's probably the only internal-gear hub that could withstand the abuse of BMX-style riding
More exotic / improbable solutions:
- kick-back hub
- "inglespeed"
- The shifter cable selects between two modes, on the fly: 1) fixed-gear, using one gear ratio, 2) single-speed/freewheel, using a different gear ratio.
- The basic lesson from the kick-back hub and the "inglespeed" is: If you know how to modify the insides of an internal-gear hub, you can do all sorts of crazy things.
- The retro-direct scheme is interesting, but it's somewhat frustrating the effort you have to go to to get past the chainstay with the oddly-run crossover chain. It seems like implementing this inside a closed hub would work better?
- But I suppose engineering and machining new (tiny) parts is a whole different ballgame from making minor tweaks to an existing design.