Seat post slipping down It looks like my saddle/seatpost is slowly sliding down into the frame, so every 2&ndash;3 months I have to move it up by 1&ndash;2cm. Yet I tighten the clamp pretty tight, so I can't move the saddle by hand.

Is this a common thing? Should I fix something?

I weigh about 55kg and cycle on the road, about 50km per week. I try to lift my weight off the saddle over bumps. The bike's a hardtail.
It may seam counter-intuitive, but in the case like you describe a little grease may be the solution.

NOTE: If you have a carbon frame or seat-post, carbon specific grease and a torque wrench should be used. It's very easy to destroy a carbon frame or post by over-tightening when installing parts.


Remove the seat post and clean it and the inside of the frame thoroughly with a little degreaser.
Remove the seat post clamp if it has one (some frames have braze-ons through which the seat bolt is installed rather than a separate clamp) and clean the inside of the clamp and the outside of the frame.
Apply a very thin coat of teflon or lithium grease to inside of the clamp, and to the threads of the clamp bolt. I generally do not apply any grease to the outside of the frame.
Apply a very thin coat of teflon or lithium grease to the seat post and the inside of the seat tube - just enough to facilitate installation and inhibit corrosion.
Install the post and adjust the height.
Tighten the clamp to the manufacturers specification.


The cleaning should remove any grit or dirt that may have been working like tiny ball-bearings and allowing the post to slip. The small amount of grease on the clamp, frame and post should allow the parts to constrict and tighten evenly with out binding in one particular spot.

If, after cleaning, lubricating and reinstalling you still have a post that slips you may have a frame that has deformed, or a post that is slightly smaller in diameter than spec. You can try either replacing the collar/clamp with one that is a little "beefier" that can be tightened to a higher torque, or you use a shim like a piece of thin aluminum between the frame and the post.