What could you recommend for a seatpost, should be strong and light (31.6mm) Carbon, alu ?

I use and U.S.E carbon alien, I love it! It's not the lightest but pretty darn close. You could get it either 25mm(lighter) or 27.2. I don't know if there is a strength difference between the two, but I would guess tat the 27.2mm is stronger, just a guess. But you could get either one and then buy a shim (they have shims that would fit 31.6), I would guess that they are pretty light, they're made out of alum. and CNC'd. The combination would probably be lighter than any other seatpost, It would probably just as strong. Are you using it for a C1? I know they use 31.6, or maybe XLR8R? Well, maybe some one has a better idea.

Just get the USE Alien Aluminum post in 31.6mm. Very light, I think Nino has his at 142g cut.

I have new a use alien carbon 25.0 for sale. if interested email me at gonzalovilaseca@jazzfree.com

Look into the new thomson masterpiece, light and very stiff even for heavy riders. Great if you are more concerned with power transfer rather than comfort. The saddle clamp system is far better than USE.