I didn't go into great detail describing the potential performance advantages of internal gearing, trying to keep it simple and to the point, but since such good background info was privided by tcs...I will now.
I know many in this forum frown upon the sport of Downhill, but a few interesting developments have arisen due to the brutal environments this type of bike is used in. Just a cursory glance at the equipment will show that retaining the chain is a huge concern for a race won or lost by tenths of a second. Conventional derailleur components are derived from XC riding and racing, and need the help of aftermarket retention devices to keep the chain intact through a severe beating. One might think that an internal hub would be a perfect solution to chain slap...and it has been tried even by some big manufacturers and well-known riders, though there are issues. Here's Hans Rey, circa 1983 on an S-A 3-speed:
Although nearly anyone can employ an internal hub on a conventional bike's rear wheel, this causes a few problems, especially for suspended designs. With a straight chainline the rear triangle movement would either snap a chain or make it go slack depending upon pivot placement unless a tensioner is used, defeating the purpose of retaining the chain. Yes, the swingarm could rotate around the bottom bracket, but then chain torque would compress the suspension. Tricky to deal with.
The second major issue is unsuspended weight. Even the best internal hubs weigh a pound or two more than even a heavy duty derailleur hub. I'm not talking about the overall system weight versus derailleur, just the rear hub. This extra weight is in a very bad place for suspension. For racing speeds, keeping the unsuspended weight to a minimum allows the suspension to react quicker and keep the bike tracking the ground instead of packing up or rebounding wildly. If that concept is tough, picture how a metronome works:
As the weight is moved up or down, the speed of the metronome is changed. The same thing would apply if the weight was unmoved but increased: the metronome slows down.
The most elegant (though also not fully developed) solution that I've seen is the gearbox concept. Centered around the crank, the weight is placed where it is suspended and a lightweight singlespeed wheel can be employed at the rear for lightning quick reaction. The fact that a few big hitters have all worked on a similar concept (with varied success) tells me that once the bugs get worked out, this could be our future.
Here's Honda's proto:
Hayes:
GT's:
Suntour:
