Originally Posted by
Chris_W
...it is the seatpost clamp that is the weakest point in the setup - if the stoker turns the bars (or if I do so when manhandling the bike when stationary) then the whole seatpost, saddle, and bars move together. I'm thinking of putting a double-bolt seatpost clamp on to prevent this from happening so easily.
Careful here... just as parts might slip and move too easily it is also possible for parts to not slip and move too hard. Then instead of a benign slip you get a more severe break. Think of that seat post clamp as a fuse to handle overloads and keep you from smoking the entire circuit.