Each seat sits between the bike seat and the handle bars. It looks like it sits on top of top tube but it is actually supported via metal supports that attach to the main frame tube. System works well. I set my bike seat back farther than normal to provide more room for the seat and little one. Loved the ability to constantly interact with the little ones while also be aware of what in front of you. We used two systems, one for each kid and until the kids were 3 o4 4? Happy to deliver within reason in greater victoria. someone else turn to enjoy the seats.