Originally Posted by geo8rge
Get a collar that's similar to this. That should fix it.
If not, this is from a slipping carbon seatpost BF discussion. You could try the paste for carbon posts. But usually aluminum posts require grease.
You can buy tacx carbon paste at competitive cyclist.
Grease/nogrease is a controversial subject. You can't go wrong though with paste designed for carbon. The general consensus among manufacturers is no grease. This makes sense to me because as you have seen, greasing requires much more clamping force to acheive the same friction force as without grease or with paste.
I think the risk of using nothing at all is getting your seatpost stuck.