Re: Shifting gas bike idea
I have been thinking of running a cheap bike this way. If you use a frame that takes the old square-taper spindle (common stuff, really), and get a matching cheap crank, you can have cranks on both sides of the spindle.
This will make a bicycle that REQUIRES the operator to pedal while the engine is engaged.
This is not as bad as it sounds if you have a reliable clutch lever and kill switch, and/or you use a centrifugal clutch.
If it was a bike geared like a "10 speed", you will have plenty of top speed and plenty of ratios to save your legs.
If you have BMX pegs on your rear axle, you don't even have to pedal the bike once you get started, and still have full hand controls. If your frame is small enough, you can still sit on the seat conventionally with your feet on the BMX pegs.
I like it. The biggest problem will be matching or tensioning the chain on the motor side.