Quote Originally Posted by sgtiger View Post
My $0.02 for what it's worth:

I'm not sure if the same problem would exist with the trailer as we have with our tag-along bike that is seat post mounted but having the attachment there seems to affect Dh's center of gravity enough that he has to compensate for it and he really feels it when DS is wiggling around. Friends who have tried both the seat post mounted and rear-rack mounted tag-along bikes prefer the rear-rack mounted ones because the additional weight is then distributed over the rear wheel which they have reported feels more stable. I know with our Chariot, which is mounted on a rear wheel skewer attachment, I do not have any issues with DD's movement affecting my balance. Then again, the problem might not be as bad with the trailer because the weight of the load is lower and distributed between two wheels and the seat-post mount, as opposed to the load being only on top of one wheel and it's attachment point.

Perhaps someone who understands the mechanics of it better can chime in and explain it better.
I'll second that. I've ridden both with a child in a trailer attached to the rear dropout and with a child on a trail-a-bike attached to the seatpost. The trailer is perfectly stable. The trail-a-bike is not. Probably due to the high attachment point at the seatpost combined with the high center of gravity of the child. There also seems to be some play (or dual stability?) in the way the trail-a-bike attaches, because you can see and feel the trail-a-bike lurch from one side of the adult bike to the other when the child moves. I've also found that the drops feel more unstable than the hoods when towing a trail-a-bike (because they are below the seat post attachment point?).

Can someone name a brand of trail-a-bike that doesn't attach to the seapost?