Originally posted by heydad2
The seatpost isn't the original one. It has been replaced by the LBS before I saw the bike. I didn't know that Kalloy made Ritchey. Would the 400mm Ritchey make a difference, considering that it has more area in the seat tube.
If it's a Kalloy it's a pretty stout post -- almost as thick as a piece of galvanized pipe in cross section. Also, if the max height line is not showing I wouldn't bother with a longer seat post -- it wouldn't make much if any perceptible difference.
The two places I would be looking for any excess movement would be:
1. Your seat, i.e., is there a lot of padding or are the rails coming loose from the shell OR
2. Your stoker is just pulling on their handlebars pretty hard, which does make it feel like the seat post is flexing since the whole bike is being moved around under you.