After 15,000 miles of riding a tandem, had a first happen this weekend: ejected my stoker off the back of the bike. We were doing power starts, a drill for developing power where you put the bike in the 53/11, and start out of the saddle from a standing start and go as hard as possible for 15 seconds. We've done these before without incident, on single bikes and the tandem. This time on the second or third stroke, we threw the chain on the back. When the chain came off, we're applying maximum force, and all the sudden no resistance. The combination of no resistance, my force pushing the cranks around, and the rear handlebars turning under the forces threw my stoker off the bike sideways (while I continued stokerless down the road for a few feet). Needless to say, we made quite sight in the middle of the intersection (we were starting out from a stoplight).
The chain came off the big ring to the outside. I put the chain back on, checked that everything was adjusted correctly, (the limit scew for the front derailleur was fine)and we concluded it was just a freak occurence. So we tried it again. This time the chain came off to the inside, with no incident this time because we were prepared.
Power starts are part of our normal base phase workout, and we've done them before on this bike ( A Burley Duet) without incindent. The only differnece is we've recently replaced the front chain rings. Other than this incident, they work fine.
My only conclusion is that the big ring flexes too much to take the abnormal force put on the drivetrain by this drill. So we're not going to do power starts on the tandmen anymore. I'm not really expecting an answer here to this rather unusual problem, Just thought you guys might find this odd occurence interesting.
And by the way my stoker, is fine albeit with alittle road rash, but a good sense of humor.