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  1. #1
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    Need help with seat post

    Hi all. Recently purchased a used 2008 Specialized Expedition Sport. The seat post was just a few inches too short for me, so I bought this guy to replace it. The specs on the bike page say its a 27.2 mm seat post so it was an easy choice when I was deciding what size I wanted. However, when I got the seat post today it didn't fit! Then I learned that the size of the seat post is on the seat post. Apparently its 30.9 mm. I think luck might be on my side though because its a little too small, rather than a little too big. Should I just get a new post (I don't see many options at that size and would rather not return it to Amazon) or should I just get a shim? I am not quite sure how they work. Do I need to get one that goes exactly from 27.2 to 30.9 or is it more like a range of widths? For example, if I got one that was for 27.2 to 31.6, would the shim work for any value in there? Or are is it an exact thing so that the shim can be fully inserted into the post hole?

    Thanks for the help!!

  2. #2
    Ride, Wrench, Swap, Race dddd's Avatar
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    I think I have seen a two-piece shim used that can take up a variable amount of slack.
    I haven't messed with them though.

    Now in this case, it's obviously the new post that is 27.2, and yes there are sized shims for that common adaptation and this is preferable to a multi-fit shim which may be improper for modern or high-end frames made from better materials.

  3. #3
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    i think it may be time to learn how to return an item to Amazon.

  4. #4
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    Shimming is fine as long s the shim is 3" long. However 30.9 is common readily size, and in your shoes I'd go for the right post over a shim. See if you can return your post, or put it up on ebay.
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  5. #5
    Ride, Wrench, Swap, Race dddd's Avatar
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    Yeah, come to think of it, I needed a rare-sized (25.6mm) seatpost with a zero-offset, micro-adjustable head.

    I thought "Good luck finding that, it's an Austrian vintage bike size.", but a quick Googling session immediately produced a fine specimen, for only $20 (shipped) thru Amazon. Delivery was about 4 days.

    A shim might cost half that much, but the correct-size post might ship out immediately with the wrong post collecting the charge-card credit later?

    This silver, 2-bolt post was very light even at about 18" long! I cut 90 grams of length out of it:

  6. #6
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    Quote Originally Posted by hueyhoolihan View Post
    i think it may be time to learn how to return an item to Amazon.
    +1 Order the right size.

  7. #7
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    A quick check shows a shim is about 2x the price of your seatpost. Returning an item to Amazon is a snap (especially if it's a "Prime," which pays for the return shipping), then buy a seatpost that fits.
    Chiunque tenti di scappare a queste regole dovrà mangiare un piatto largo di polenta vecchia di tre settimane e sarà schernito per questo, soprattutto se è straniero

  8. #8
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    30.9 millimetres = 1.21653543 inches

    You know, I understand the imperial/metric situation, but how on Earth did we end up with the situation where there are just so many different seat-post sizes?

    Or is that just a 'metricated' version of 1.2" in this particular case?

    Surely tube manufacturers like Reynolds et al, if they have been making tube-sets specifically for bicycles for years, would have benefited from using just a few standard, more rounded sizes than the plethora that exist now?

    Edit: Doh. I found out, and it's pretty obvious now I think about it - it's all because the seatpost has to fit down the *inside* diameter of the seat tube, which can vary because of the different buttings etc. used over the years as tubing has evolved.
    Last edited by Continuity; 04-06-13 at 05:43 PM.

  9. #9
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    Alrighty, looks like I'll be looking for the right size post. Thanks all!

  10. #10
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    There's *loads* of 30.9mm ones to be had on Amazon, for example - here is an inexpensive FSA one, and here is a more spendy Ritchey Pro one.

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