I found these videos to be helpful - please add to this! There's a lot of vocabulary to wrap one's head around. (I feel like I'm back in school and writing a lesson at the same time)
A nice walk around of what makes a scooter go. "How Scooters Work by Jessica"http://www.youtube.com/watch?v=k5tErEP70rs&feature=related
At 4minutes :30seconds, she talks about the CVT (Constant Variable Transmission)
. Ah ha! A CVT has a variator (the 'disc' on left in photo below), a clutch (the 'discs' on the right), and a belt which connects the two together
Inside the variator are rollers
which are also called weights
. As the variator spins, the rollers move outwards to the edges of the disc. This makes the belt move outward which changes the power ratio. As this happens, the clutch also engages, spreading the cluth discs apart which makes the belt moves downward (inward). See the video that Ellen suggested a good description on how the power ratios change.
Now those rollers can be replaced by what is called a sliding rollers (or sliders)
. This advertisement shows what they look like:http://www.youtube.com/watch?v=IyuC-LQE6Vk
And to see what it takes to replace them, see this videohttp://www.youtube.com/watch?v=hyb9NyR-Sjs&feature=related
Another explanation that also works: http://motorscootermuse.com/stepless.php
Now the challenge is how to get max torque when you're already going... like for uphills. There's probably some technique that helps get some umph that is similar to downshifting a manual transmission.