It's actually pretty cool. My understanding is that there's no spring in the derailleur, and the tension between the two cables is what maintains the parallelogram. It's actually a pretty sweet setup, since you have to find the gears on these as you go, there's no indexing (I think I'm going to get this pretty closely dialed in, though). Instead of having to take your hand off the grip and find a shifter, the whole thing is right there in your palm. You get a lot of feel.