I did a Texas hill country tour in 1979 with two other riders. They were on a Schwinn Paramount tandem - these guys were twins and they were outstanding riders. Back then, Whit Snel had the Schwinn franchises in San Antonio (owns Bike World today) and these guys both worked for Whit.
When we were going down hill, that tandem would take off like a locomotive going downhill. Often, when we'd hit a big hill, I'd reach over and grab their rear rack. It was like the hand of God was giving me a shove. I must have been more stupid back then than today - inches away, one hand on my bike, the other holding on to a tandem.
Sheesh.... that was fun.