I'm with Roger.. borrow/rent a tandem for a few 30 to 60 mile rides and see how that goes.. the g/f may not be as happy riding as a stoker as the captain (unobstructed views, no sweaty body blocking the wind etc.).. captain gets the sweet ride being in the middle of the long wheelbase, stoker not so much.. with 20" wheels, you'll probably want much more than V-Brakes for the long downhill runs so you won't overheat the rims and blow the tires .. you pick up much more speed on a tandem downhill .. I'd want discs .. my 26" tandem is an older model with front and rear caliper brakes and an additional drag brake hub in the rear.. mine also sits mostly unused in the garage .. if you're seriously thinking tandems, I'd be looking for 26" wheel models for lots of good reasons with comfort and safety high on the list.