Metal seat post with carbon fiber frame? Is using a metal seat post on a carbon fiber frame advisable or not? I want to use a seat post mounted rack on my road bike (no regular rack mount points are on this bike), but I have been told that is not a good idea for carbon seat posts. So I thought I get a whole new metal post &amp; saddle and swap the posts as necessary for commuting versus recreation.

I ask primarily because the famous Sheldon Brown once wrote on his site "Using a carbon-fiber seatpost in a metal frame, or vice versa, invites problems." but didn't explain why.

Any thoughts?
It's likely that Sheldon's concern was for galvanic corrosion between carbon fiber and aluminum.  This is an issue that's well-trod in both the bicycle and aeronautics fields.  In essence, in the presence of an electrolyte (sea air, your sweat) and a cathode (carbon fiber-embedded resin) the anode (aluminum) will corrode.  In the case of a seatpost/seattube interface, this corrosion will wedge the seatpost in place.  This can, at best, make it extremely hard to remove the seatpost.  At worst, it can render the frame unusable.

The first thing to do is to check to see if your frame was built with an aluminum insert for the seat tube.  Given that you currently have a carbon seatpost this is unlikely, but it would alleviate the main concern.

If that's not the case, there are still some precautions you can take. As Calfee notes, anodization will provide some protection.  As well, regular removal and cleaning and reinstallation with carbon paste can help prevent excessive buildup.

On the significantly more expensive side, you could also consider a titanium seatpost, which wouldn't corrode.

I'm not sure how the formatting in this article got so ruined, but you can read more in this VeloNews Technical Q&amp;A with Lennard Zinn.