Blue Collar MTB says don't grease the post. Lennard Zinn gets word from the experts, who all say "No grease." But then carbon-fiber expert Craig Calfee responds: "I don't know where the myth started, but carbon composites are not affected by grease. Our advice is simple: If the seatpost fits tight, grease it. If it slips, de-grease it. As has been known for many years, when aluminum and carbon fiber contact each other, galvanic corrosion can start."
Craig Calfee is correct that galvanic corrosion can occur between carbon fiber and metal. Putting dissimilar electric conductors in contact -- like a carbon fiber seatpost in an aluminum tube or collar -- can result in corrosion at the contact surface as metallic ions migrate from one material the other to balance the electrical potential. The result is a seatpost that is chemically welded to the seat tube.
IMPORTANT: Please post comments for this article at the new CYCLELICIOUS 2.0 version of this page.
Get FSA's new carbon assembly compound. It is a grease-like substance that keeps your posts from slipping and prevents corrosion at the same time. This is the only product from FSA that I have really liked. In fact, I find myself using it on anything that could slip (stems, bars, bolts, pedal threads). The stuff works great!
That welding can happen with chromoly frames, too, requiring frequent applications of penetrating catalysts and whanging with hammers... but some girls will do anything for an excuse to visit the bike shop. Said seat post is a bit discolored, but liberated, and my mechanic has vowed to at least nudge the seat post on its 3000-mile checkups...