I have a Cannondale Synapse (2015 model), and have swapped the stock Cannondale seat-post for a Thomson Elite inline seat-post. However, I am experiencing problems with the seatpost slipping, even when tightening to 5Nm, as specified on the Cannondale frame. The seatpost clamping mechanism is an internal two-wedge system.
The frame is carbon, and the seatpost is aluminium. I am using carbon paste, but this does not seem to have truly solved the problem.
I am considering adding a Thomson seat post collar directly onto the seat post, but am nervous about adding extra downward stress onto the carbon frame.