Is there anything to worry about using a carbon post in a shim ? (it would be a use thermoplastic one). I have a nice 27.2 from one frame I want to put in a 30.9 tube on another. The shim would seem to be the same length as the ‘minimum insert’ line is on the post, and the post will not be at full stretch so leverage would a little less too. And yes I already use the lovely pace carbon paste. 🙂

Your wisdom or experiences please.

Don’t see why not.

But i wouldn’t bother if you move the seatpost much.