Sanding a seatpost to size?

[Gartenmeister]

I would like to reduce the size of a 27.2 carbon seatpost to 27.0. Anyone tried this? Tips? Recommendations?

I was thinking to start with a razor blade "scraping" (commonly used to remove clearcoat/logos) and then just hand sand it. Not sure what grit to start with.

Any better ideas?

[bikerboy337]

I'd buy the correct size post.

I dont take any chances on parts that will cause me to crash if/when they fail. Contact point, wheels, not areas i'd modify personally...

[palincss]

I reduced the size of an aluminum post by a small amount. It took a lot of patience, and an assortment of grades of sand paper, from 80 to I think 400. In my case there was no "correct size" option: I learned from the previous owner there had been an issue with the size from the day the bike had been delivered, and on account of something that happened in the build process (I'm vague on the details) it ended up being between official sizes. The "correct" size slipped and the next one up was extremely difficult to adjust.

I don't think I'd try it with carbon.

[cnighbor1]

are you sure frame takes 27.0 mm
Maybe it needs reaming to 27.2 mm

[notsew]

Seems like a massive PITA.

If you do, make sure you wear gloves and a mask.

[Corso]

True tale: Back in the early 90s, I bought a cheap 1/18 aluminum quill stem-for a 1” headset bike. Doh, My mistake.

Because I didn’t pay a lot of money for it, I went to work with a file, and hand ground that sucker to fit. Heck-the quill wall was pretty thick--Looked just fine!

After everything was all together, and a few test rides, I was feeling good with myself.

The I "woke up", took it off and threw it away. The thought of that stem snapping while racing made me realize of how stupid I was.

I think this is the first time I’ve admitted to doing this foolish thing...

Do you really want to compromise that seat posts strength? I’ve seen a few carbon posts break.

[charliedid]

Originally Posted by Gartenmeister

I would like to reduce the size of a 27.2 carbon seatpost to 27.0. Anyone tried this? Tips? Recommendations?

I was thinking to start with a razor blade "scraping" (commonly used to remove clearcoat/logos) and then just hand sand it. Not sure what grit to start with.

Any better ideas?

I recommend no.

[mtechnica]

I seriously doubt .2mm sanded off a seatpost will compromise its integrity. Could take a while to sand it though. Also, in the past, I've fit a greasy 27.2 post in a 27.0 frame without even doing anything to it but YMMV

[JAGI410]

Are you out of your damned mind? NO!!! It seems like an insignificant amount to remove, but it's not worth the risk. But if you're willing to test the sensation of a sharp broken Carbon tube colliding with your genitals, go for it.

[dem]

Dissenter here.. if it is an even color (ie, you cannot see the weave of the carbon - it is a uniform black) it likely has a cosmetic top layer to even it all up.

Try the razor blade method and see if it comes off, totally fine. If anything, you'll be able to see any future cracks better!

(Disclaimer: I've ridden a cracked carbon seatpost for 10,000 miles, so I am maybe not the best person to take advice from. In this case it was the reverse problem, the post was slightly undersized, so the clamp cracked it a bit. I just kept an eye on it and it never moved.)

[Peter P.]

If it's a carbon seatpost, then don't do it. If you think you can reduce the clearcoat by a mere 0.2mm then you know more than I do. If you cut through any of the carbon fibers, then throw the post away.

If it's an aluminum post you're referring to, then I suppose it's possible but extremely time consuming. I'm inclined to think all aluminum posts from manufacturer X are created from the same blank and only the O.D. is machined to the correct diameter. If my theory is correct, then there is sufficient material to turn a 27.2mm post down to 27.0.

A problem I see is trying to sand an aluminum post. Sanding aluminum will gum up sandpaper pretty quickly, rendering it useless. You would be better off cutting it down with a lathe.

[kingpin75s]

Regardless of other considerations discussed, I would be concerned about the ability to keep it truly round as it is sanded leaving uneven contact with the seat tube.

I would fall in the not recommend category if there is a count

[FlashUNC]

Just sand the point into a spear. Save you the trouble from the inevitable breaking.

[cachagua]

Second on getting the frame reamed.


Oh, wait -- it's a carbon frame?

[ripvanrando]

Just use more KY