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Has anyone cut their seat post for the sake of saving some weight? Is there a certain length the tube has to be seated into the frame?
tubing cutter? was that a carbon post?Gearhead65 said:I have a KCNC zero setback that I cut approx 8 cm off. Used a tubing cutter. Just didn't need that much and I still had plenty in the frame....and I'm a weight weenie.![]()
1.) Sorry, as an engineer I do not see your logic of the maximum support being reached when the length of insertion = diameter past bottom of the TT. It just is not true. The seat post insertion needs to resist the moment created by the load on the end of a cantilever. the longer the cantilever, the more moment resistance you need. More insertion = more resistance. I would expect a longer seatpost to have a longer minimum insertion, thus if you cut one, in theory you would not need as much minimum insertion. To be safe, I would maintain the minimum insertion length as marked by the manufacturer.Peter P. said:The seatpost remaining after you cut MUST extend BELOW the bottom of the top tube, a distance at least equal the diameter of the seat tube.
For instance, if your seat tube is 30mm in diameter, then the seatpost should be long enough to extend 30mm below the bottom edge of where the top tube and seat tube intersect.
The reason is, you don't want the leverage of your seatpost as you sit on it exerting maximum force on the seatpost clamp or the joint of the seat tube/top tube. Maximum support is reached when the length of insertion equals the diameter of the seat tube.
Make sense?
Do not cut your post with a tubing cutter. It will flare the end and you'll have to file it afterwards so it will insert into the frame, and it won't look as professional. Use a couple of hose clamps cinched around the post at the point of cut, and a hacksaw. Clean up the joint with some sandpaper, which should be minimal.
+1 with Maytag Blue.Blue CheeseHead said:1.) Sorry, as an engineer I do not see your logic of the maximum support being reached when the length of insertion = diameter past bottom of the TT. It just is not true. The seat post insertion needs to resist the moment created by the load on the end of a cantilever. the longer the cantilever, the more moment resistance you need. More insertion = more resistance. I would expect a longer seatpost to have a longer minimum insertion, thus if you cut one, in theory you would not need as much minimum insertion. To be safe, I would maintain the minimum insertion length as marked by the manufacturer.
2.) When cutting with a pipe cutter the flare is created on the inside of the post, not the outside. Even without filing, it will not impact the ability to slide into the seat tube smoothly.