30.9 post in a 30.0 frame?

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30.9 post in a 30.0 frame?
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Posted: Nov 24, 2009 at 19:38 Quote
Anyone know if you can make a 30.9 seat post fit in a 30.0 frame?

Posted: Nov 24, 2009 at 20:48 Quote
seat posts are so cheap even for a high-end one just get a new one

Posted: Nov 24, 2009 at 20:53 Quote
please don't try to sand/file/mill down a 30.9mm seat post to 30.0mm... Seat posts walls are thin enough these days, and losing 0.45mm off the thickness of the post can be catastrophic. As in it cracking in use and opening up a 2nd butt hole for you.

Posted: Nov 24, 2009 at 21:00 Quote
singlespeedtoday wrote:
Anyone know if you can make a 30.9 seat post fit in a 30.0 frame?

NO. Simple as that.

Posted: Nov 24, 2009 at 21:07 Quote
I'm not going to do anything to my post.

Don't be so sure of yourself unless you can prove it won't work. I have fit 27.2 posts in 27.0-26.8 frames before so I thought it could be possible.

Not a big deal if it doesn't work.

Posted: Nov 24, 2009 at 21:24 Quote
singlespeedtoday wrote:
I'm not going to do anything to my post.

Don't be so sure of yourself unless you can prove it won't work. I have fit 27.2 posts in 27.0-26.8 frames before so I thought it could be possible.

Not a big deal if it doesn't work.

Ok, I am just saying. without modifying your frame or post it won't fit. and if you do modify either one you will greatly reduce the structural integrity of the part.

plus, you are talking almost one millimeter difference in diameter... that is a lot compared to 0.2mm.

Posted: Nov 25, 2009 at 2:26 Quote
its not worth it

your frame generally costs alot more than buying a new seatpost

trying to fit a post that is too large into a seat tube that is too small, is a sure fire way to crack your frame (you are stretching the seat tube)

0.9mm is actually a big difference in terms of engineering tolerances

Posted: May 17, 2022 at 2:44 Quote
I know this thread is old and dead but for anyone currently trying to find info on this, it is possible, but only with overbuilt frames like the old konas and norcos.

***Search for the "Seat tube reamer/facer"***, it is what they use for building frames.

30.0-30.9 is only .9 of a millimetre, as it is a cylinder, you only have to take off .45mm of material to make the post fit.

The seat tube reamer is the appropriate tool but I've also heard this can be done with a flex hone and a lot of patience.

Note: this isn't something you should do if you're clueless like the people who say it can't be done ;p if you have a good mind for mechanical problems you should be able to tell if you're frame can handle .45mm of reaming

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