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Old 07-24-07, 07:30 AM   #1
Bob Loblaw
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27.0mm vs 27.2mm seatpost

Can a 27.0mm seatpost be used in a 27.2mm tube? The difference in diameter is less than .008".
Thanks!
Bob
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Old 07-24-07, 07:35 AM   #2
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Originally Posted by Bob Loblaw View Post
Can a 27.0mm seatpost be used in a 27.2mm tube? The difference in diameter is less than .008".
Thanks!
Bob
If you do it, you'll find yourself feeling "taller" (and the bike feeling smaller) during the course of each ride-
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Old 07-24-07, 07:42 AM   #3
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Took me a minute, but I eventually got it... ;-)
Seriously though, it really makes that much of a difference? I can't believe that an average seatpost has a diameter tolerance of much better than +/- .005". To think that a .008" difference would cause slippage? I've never tried it, so I'll trust your opinion, but boy that sure surprises me...
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Old 07-24-07, 07:43 AM   #4
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Took me a minute, but I eventually got it... ;-)
Seriously though, it really makes that much of a difference? I can't believe that an average seatpost has a diameter tolerance of much better than +/- .005". To think that a .008" difference would cause slippage? I've never tried it, so I'll trust your opinion, but boy that sure surprises me...

Put it this way: they don't specify 26.8, 27.0, 27.2, etc. for nothin'-
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Old 07-24-07, 07:49 AM   #5
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I ran a 26.8 post in a 27.0 environment (mismeasured at first) and well biked's prognostication is correct.
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Old 07-24-07, 07:51 AM   #6
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Yeah, it makes that much of a difference. There was a thread, not long ago, about this very topic, although there the problem was to fit a 27.2 mm (very common) seatpost into a 27.0 mm seat tube.

In fact, I'd need a 27.0 mm seatpost, so if you don't need it (as you seem not to), we might come to an accord. Leave me a PM if you're interested.

BTW, should I dig up that thread? It makes for a fun read.
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Old 07-24-07, 08:43 AM   #7
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I was going to say use a shim, but i looked around and I don't see any that small. I found a sheet metal gauge calculator, and that size (.008")looks like 32 gauge aluminum. you could try that if you are really attached to your seatpost.
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Old 07-24-07, 09:08 AM   #8
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I was going to say use a shim, but i looked around and I don't see any that small. I found a sheet metal gauge calculator, and that size (.008")looks like 32 gauge aluminum. you could try that if you are really attached to your seatpost.
No, I'm not attached at all to it. I'd just like to use it for sizing purposes (length) before I go and purchase a new one of some specific length. This is going on a new frame I've never ridden, so I just want to be sure I'm buying a post that is the appropriate length, but not excessively long.

EDIT- PS, You can get shimstock in all kinds of thicknesses (down to .0005"!) check out www.mcmaster.com. Just in case you ever need it!

wroomwroomoops: The post may be available soon. I'll have to check the exact model from home, but it's a Bontrager. I don't believe it has any setback. Once I get the wheels on the frame, I should be able to get a rough idea of what length I need, and can purchase the right diameter.
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Old 07-24-07, 09:35 AM   #9
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You could always try a coke can. The aluminium is very thin. I heard it done before but never did it myself. It might work.
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Old 07-24-07, 10:37 AM   #10
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Originally Posted by Bob Loblaw View Post
. I'd just like to use it for sizing purposes (length) before I go and purchase a new one of some specific length. This is going on a new frame I've never ridden, so I just want to be sure I'm buying a post that is the appropriate length, but not excessively long.
It will work long enough for you to test for post length, but don't really need worry about buying one too long. The last post I bought was a 350mm - just cut it to length after I was happy with the saddle height.
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