It was one of those “What the heck just happened?” moments: Eldest Son’s bike chain jumped off the rear sprocket and jammed itself into the frame, bringing his bike to a sudden and unseemly halt, which really made him jump. Of course the bike did this as far away from home as possible. After about ten minutes of muttering from Daddy we were able to continue, a bit quicker because we were now running late, and the same thing happened again ten minutes later. This time Eldest Son felt it happen and brought the bike to a controlled stop: he learns fast.
At the time, finding the cause of the problem was less important than getting home in time for lunch. Thank goodness for Xtracycles, although hauling a bike like this is very odd -the bike wobbles all over the place and seems to have a mind of its own, and we get so many people looking I could probably carry advertising. Unfortunately my legs were complaining seriously after schlepping this lot and eldest son back home, so I doubt a future career in low-impact marketing beckons.
The chain tension was fixed in five minutes, plus another 20 reading Sheldon Brown and trying to figure how to get a Nexus gear hub off the axle.
(It looks like we aren’t the only ones to transport bikes like this. That’s always comforting)