I don't understand...

[Mr Gear]

http://www.youtube.com/watch?v=z4PAzalfpww

[MagicalTrevor]

Which part? The rear hub will work on a ratchet pulled by the elastic bits attached to the pedals. Seems pretty straightforward to me but not sure how efficient this would be

[Mr Gear]

Apparently it's more efficient than a chain. But there are so many unanswered questions... is it heavier? Can you add gears? Is it as tough as a chain?

I still can't quite get my head around the animation, because the rear pulley thing doesn't appear to wind back... and logic dictates that it should. Perhaps it is just a detail that the animation cannot show.

[Hard-Drive]

Watched it a few times...I think the bit on the chainstay is fixed, and you change gears by moving the position of the little wheels on that cranky thing, in towards the BB for power, out for speed.

Looks complicated, although I can imagein you'd get a good spread of gears. Seriousness of application however is perhaps in line with design of frame...not nice!

[ezi]

I'd imagine that would be awful to ride, despite it perhaps being more efficient.