Hub generator? Bottle generator? An '80's bottom-bracket mount generator?
None of the above for me. Nighttime cyclists in this city have the same goal as denizens of the club scene: being seen. Here, flashing lights are more useful than steady-beam lights because most streets are relatively well-lit. As far as I know, none of the generator lights made today has a flashing mode.
But I can think of another kind of generator that might be useful here, at least in the summer. Here it is, in action:
Now tell me: You really want to use your bike to make ice cream. Admit it!
Once you do that, there's no telling how many appliances you can power with your bicycle. Hair dryers. Laptops. Juicers. How about a sandwich press? After all, what's better than a panini for a mid-ride snack?
Forget ethanol or solar, wind or nuclear power. You just saw the real solution to the world's energy needs!
