Ok, I just bought a Giant TCX Frameset. While it came with a shim to allow fitting a 27.2mm seat post, is that size really the best choice? Can't I put a 30.8 (or is it 30.9?) seat post in it and ditch the shim?

My LBS heard that it would void the warantee though if I used a larger post -- can anyone confirm this? What's the real story on these?

Thanks!

I just got of the phone with Giant USA. They said they will not honor a warantee if you use anything but a 27.2mm post. Can this really be right? What can go wrong?

I'm not sure what could go wrong, but it's possible the seat tube is not 30.9 the entire way down, and you may have to force a post down if it were that size. Also, the tubing may get thinner further down, potentially causing the post to damage the frame.

Again, I'm not sure that's the reason, but that would be my guess.

Ok, I just bought a Giant TCX Frameset. While it came with a shim to allow fitting a 27.2mm seat post, is that size really the best choice? Can't I put a 30.8 (or is it 30.9?) seat post in it and ditch the shim?

My LBS heard that it would void the warantee though if I used a larger post -- can anyone confirm this? What's the real story on these?

Thanks!

The voiding of the warranty is true. I have a Giant TCR roadbike with the shim to accommodate the 27.2 post. The shim seized to my Easton carbon post and ruined it. So I removed the shim and have been running a 31.8 Easton carbon post with absolutely no problems whatsoever. I think you'll be fine running it without the shim. The diameter in the seat tube is consistent. You just need to make sure you have enough seapost in the tube. Hope that helps.