Today on a ride the seat bolt broke on the stoker saddle. We were going about 20 mph when the bolt securing the saddle to the rails broke. My poor wife fell back with her backside rubbing on the rear tire before she was able to lift herself up and I steadied the bike to a stop with saddle and seat rail clamps crashing to the road. She has some respectable road rash from the tire on her backside. Needless to say she (we) was very frightened. Thankfully she was holding onto the handle bars when it occurred and we did not crash.
This is the second time a bolt has broken on the stoker saddle. The 1st bolt, broke about two years ago, and was the original bolt that came with the seatpost (woundup) and the 2nd bolt was from the hardware store. My wife weighs 135 lbs, so I don't think her weight is an issue. We ride a Co-Motion Supremo.
My theory is that she likes to sit back on the seat at times, as she is a little cramped in her riding position, when we are not riding hard and the pressure of being so far back on the seat eventually leads to the bolt breaking. Also, she sometimes sits up without hands on the bars to enjoy the country side as staring at my back does get a little tiresome.
Your thoughts on what might be happening?
My thought is to get a set-back seatpost to give hear a little more space, but it obviously won't be much.