I have several children and two Trek Mt. Train 206 "pedal trailers" (a/k/a "chaser bikes, trail-a-bikes, trailer bikes") that my wife and I use with kids. Once rigged up, we're basically a three-wheeled tandem, or trandem, if you will. Our pedal trailers have six speed derailers and single chainrings. On a tough hill, I can actually feel a push from the rear when I ask my son for help.

All of this has made me think about an adult+adult varient: a high performance trandem.

I am 6'3". My wife is 5'0". I ride a 58cm road bike and she rides a 50cm. As near as I can tell, there are no traditional tandems which will fit us -- or can be made to fit us -- for less than the price of a used car. We like riding together, and we'd like to try tandeming, but throwing down many thousands of dollars for a tandem to fit us seems extreme.

And this made my think even more about an adult+adult varient: a high performance trandem.

Has anyone built a pedal trailer for an adult? With a lightweight frame and good components? It seems to me that this could be a heckuva alternative to a traditional tandem. Granted, it could never be as light as a traditional tandem. Advantages for the total rig (captain's bike + pedal trailer): (1) it would be less expensive, (2) it would store/rack more easily, since you break it in two, (3) the stoker would not be required to pedal at the same cadence, or at all, (4) the stoker gets a slightly better view than just the captain's arse all day. Disadvantages: (1) more drag, (2) longer, (3) heavier, but probably not a lot more of any of those.

I grant you, a trandem would not be the choice of anyone serious about tandems. But if you already have a captain's bike you like, then for less than the price of a comparable road bike, you and your favorite can be riding as a team. My wife and I like to ride together, but she's just not as stong as I am. Even if we could afford a tandem which would fit us, I worry that her inability to coast would be bothersome to her. With two totally separate drive systems and freewheel hubs, she could pedal as she pleases.

Totally crazy?

There are/were adaptors, like Cyclemorph that will cost you around $600. cyclemorph.com
Tandemrack, a wannebe tandem system, costs about $120. You attach/detach second bike to first bike. HYPERLINK https://www.x2cycle.com
Both of these systems were at the Interbike show in 2005.
Caveat: have seen it, but not tried it.
Our opinion: try a real tandem. Learn how to ride/communicate on it. Coast when stoker asks.
Borrow, rent or purchase an inexpensive used tandem.

I saw your post. My company is x2Cycle that makes the Tandem Rack. It was developed for exactly the type of situation you describe-- riders of uneven ability (works for 2 adults or an adult & child) that want to connect occasionally. You use your regular bike & can go from connected to riding individually in about 5 seconds. Check out our web site at x2Cycle.com. If you try one & it doesn't work how you expected, we have a 60 day money back guarantee. Best of luck whichever way you go.