Originally Posted by carpediemracing

Another thing is the middle ring may not be a middle ring, i.e. it may be missing the cutouts to allow the chain to move off to its inside. I bought a new middle ring for our tandem and realized after that it was a "small ring for a double", not a "middle ring for a triple". So it's sitting in my parts box for now.

I used to file down teeth (1 almost all the way, 2 about half way) to "ramp" unramped chainrings. You might be able to do the same thing to assist the chain.

An easy way to tell is if it has pick up pins on the inside. If it does, it's meant to be a middle. If it doesn't, it's meant to be a small.

Originally Posted by carpediemracing

I am not next to our Cannondale tandem but if the seat tube is round and of reasonable diameter, you can put on a "chain watcher" or some other device to prevent the chain from dropping off the small ring (I prefer N-Gear's metal thing to the standard chain watcher). Then adjust the derailleur to overshift by a lot and rely on the watcher to keep the chain on the ring. Unfortunately if the derailleur is toward its inner limits, the spring tension is not substantial.
cdr