reaming seat tube .2 mm larger
10-25-22, 02:34 AM
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reaming seat tube .2 mm larger
hi all, i have just built my first frame and i'm busy finding all components and assemble everything to see if all fits before painting.
The only problem i face now is that i have a seat tube with an internal diameter of 30.7 (Columbus ZON113635002) and can't find a good seat post for this.
i can buy a reamer and ream it to 30.9mm but i'm not sure if it's wise to take off 0.2mm of a tube with the wall thickness of 0.5 to 0.9 at the end.
or would it be better to use a 30.2mm seatpost and not worry about the 0.5mm of slack?
any advise would be really helpful
The only problem i face now is that i have a seat tube with an internal diameter of 30.7 (Columbus ZON113635002) and can't find a good seat post for this.
i can buy a reamer and ream it to 30.9mm but i'm not sure if it's wise to take off 0.2mm of a tube with the wall thickness of 0.5 to 0.9 at the end.
or would it be better to use a 30.2mm seatpost and not worry about the 0.5mm of slack?
any advise would be really helpful
Last edited by jasperV; 10-25-22 at 03:06 AM.
10-25-22, 05:16 AM
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That seat tube is meant to take a 30.6 seat post. Thomson makes a seatpost in that size or find a shim to go from 30.6 to the size post that you want to use. This is one of those things that you will remember in the planning for future frames.
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10-25-22, 07:35 AM
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I had a thread about this recently. I still haven't given up on using a 30.9 seatpost, but you need to find a tube that takes that size. Which is a pain. In my case because I want to use lugs. If you aren't using lugs, then just get the right seat tube. A 30.2 seatpost is definitely going to slip in that tube. I think your only choice is to get a shim, and the only ones I have seen get you down to 27.2
Deda(?) used to make a seat post for that size and you can still find them used sometimes.
Deda(?) used to make a seat post for that size and you can still find them used sometimes.
10-25-22, 01:33 PM
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yeah i think i don't have another choice then to use a reducer. in hindsight i really had to use a different seat tube. But hey, it's all about learning from it
10-25-22, 07:31 PM
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agree with prev post to use a Thomson post in the correct size (if an option)
having said that
have two Schwinn Paramount bikes with Tange Prestige frames (Asian; one TIG'd, one lugged) - the seat tubes on both bikes were reamed so 26.8 seatpost could be used instead of OEM 26.6
the frame builder / friend that reamed the seat tubes also reamed the seatposts of three other similar Tange Prestige frames to use 26.8 post instead of 26.6 (Schwinn Paramount ; Asian lugged)
Can't recall the frame / tubing wall thickness ? .8 / .5 / .8 ? or possibly .7 / .4 / .7 ?
At the time (early 90's) a quality 26.6 ATB post was next to impossible to find - this was before Thomson posts were available
having said that
have two Schwinn Paramount bikes with Tange Prestige frames (Asian; one TIG'd, one lugged) - the seat tubes on both bikes were reamed so 26.8 seatpost could be used instead of OEM 26.6
the frame builder / friend that reamed the seat tubes also reamed the seatposts of three other similar Tange Prestige frames to use 26.8 post instead of 26.6 (Schwinn Paramount ; Asian lugged)
Can't recall the frame / tubing wall thickness ? .8 / .5 / .8 ? or possibly .7 / .4 / .7 ?
At the time (early 90's) a quality 26.6 ATB post was next to impossible to find - this was before Thomson posts were available
10-25-22, 11:09 PM
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It seems like they aim for .6 wall on most seat tubes, and OP's is most likely .6mm thick. I'm not sure about one that is going to end up at 26.6. Hopefully it was thicker. If it was .8 then you might be able to get away with .2mm, because it would end up thicker than most modern seat tubes at .7. If it's already in a lug, you can ignore the fact that you are making it too thin and it might not crack. I don't think a .6 wall is going to be enough to ream it out .3mm.
