Quote Originally Posted by NbyNW View Post
... I do have an SRAM DualDrive on my Dahon that has three settings. ...

1. You can shift while a stand-still. Great for city riding, as I often find myself stopped at the bottom of a hill.
Actually, with the DualDrive, it may be good to shift the hub only when stopped. Or certainly while not pedaling. Google DualDrive failures in trikes for more info.

Quote Originally Posted by NbyNW View Post
Not quite. The multiple chainrings are still mounted on the rear wheel. There is a single chainring up front.
You could actually also have multiple chainrings in front. With 3 chainrings, a 9 speed cassette, and the three DualDrive settings, that would be 3*9*3 = 81 gears!