Originally Posted by
icemilkcoffee
I have a 25.4mm carbon seatpost together with an adapter shim in my road bike which takes a 26.8mm seatpost. It would gradually slip down over time. I am tightening it to 'scary tight' and I am using carbon paste, and it still slips. What gives? Is this how 25.4mm seatposts are ? Or are adapter shims prone to slipping somehow?
Adapter shims introduce a whole other level of imprecision to fitting a seatpost.
Is your shim for a 25.4 to 26.8 specifically? Is it aluminum or Delrin? When it comes to shimming a carbon post, you’ll have better success with a shim that is as long as possible and that fits somewhat snug as you go to set the post to your desired seat height.
I put a 27.2 carbon post in my 30.0 ti frame with the correct size sleeve in aluminum and it made an annoying “tick” sound and then my Hope seat collar bolt broke twice when I overtorqued it. It wasn’t until I went with a U.S.E. branded Delrin sleeve that was a bit thicker than I thought I needed. I pushed it in with copper antiseize and found a stronger bolt for my Hope seat collar and it never ever slipped or made any ticking noises again.