Originally Posted by
trevor1968
I have been reading about these seat posts and i am very interested because i don't exactly have all the money for a full suspension bike. what does it mean for a seat post to be 27.2x450mm. or 30.9x400mm or 31.6x350mm. these l switch around in different ways such as 27.2x350mm but anyway, i wasn't sure what those sizes were actually referring to on the seat post and do i have to match those specifications to my current seat post? thanks!!!
The numbers 27.2, 30.9, and 31.6 refer to the diameter of the seatpost itself. Whatever diameter seatpost you currently have on your bike, that's what you need. If you pull your post, the diameter is sometimes stamped on it at the very bottom.
The larger number -- 450mm, 400mm, 350mm -- refers to the length of the post. This has to do with how much of the post ends up insider your bicycle's seat tube. Some riders prefer shorter posts to save the weight. Some bicycle frames have welds or other barriers in the seat tube to prevent a post from going past a certain point. Other frames can take any length seatpost. Best is to measure your current post length. Match it if possible, or stay close to it. If you buy a new post that is longer, look insider your seat tube to see whether there are any obstructions.
Edit: Those Cane Creek Thudbuster posts look like they can simply be cut like any other post to whatever length you need. Note that such is not typically the case with suspension posts, but the Thudbuster design means that the post part is just a post.