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  1. #1
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    Giant XTC 01' seatpost size question

    I wonder if anyone can help me on this.

    I've got an 01' XTC bike. It came with a 27.2 seatpost and a shim.

    Somewhere along the way I've updated its stock seatpost to a Thomson Elite, however I kept the diameter size (27.2) and the said shim. At that time it was my LBS that did all the work/upgrades so I didn't even really know there were other options.

    I'm thinking about renewing that part and two doubts raised.

    First, are Giant seatpost sizes (non shimmed) the same all across the range and years? Will this 01' XTC take a 30.9 seatpost as my Anthem X takes, even being 10 years older or it can take some other odd size?

    Second, is there any particular reason as to why my bike came shimmed from factory other than: "it was kind of normal at that time"? Can the seatpost be upgraded to a bigger size without any issues or should I keep the shim and get a new one of the same, 27.2 size, keeping it thin & "original looking"?

  2. #2
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    Should be a 30.9. just measure it with the shim on it and get that size. I'm gessing it will be 30.9
    since there are only 3 main standard sizes for seatposts.

  3. #3
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    I haven't had time yet to look into this issue hands-on the bike. Too much work and the spare time I have has been spent riding.

    I reckon as you say it is a 30.9, but since sometimes there are minor variations I wanted to be sure. A 30.6/30.8 seatpost tube can be rather easily mis-measured, not to mention trying to fit a 30.9 on a 30.8 wouldn't be that much fun. The other way around could easily cause some problems.

    I reckon Giants use to be 30.9, but better safe than sorry.

    I also have to decide if I keep the same 27.2 diameter and shim or if I get the 30.9.

  4. #4
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    The specs i found on that year xtc showed it as having a 27.2 on them. But if it measures
    in at 30.9 with the shim or different, it would be more stiff and strong to not use a shim
    since the whole amount of the post will be supported by the seatpost tube.
    My '08 xtc takes a 30.9 so they must of changed it sometime after '01. Maybe the post is
    under 27.2 and it's shimmed out to the 27.2. I think I use my calipers more on my bike than I do at work lol! Good tool to have around when you work on bikes.

  5. #5
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    I have to get one of those calipers to measure stuff. They're really useful!

    My post is 27.2mm, that I'm sure, but it is using a shim. I've got to measure the frame's inner diameter without the shim!

    One more tool to go on the acquisitions list!

  6. #6
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    lol, yea! I'm thinking we're back to the 30.9mm then. But if you check the post with the shim on it...
    it will be easier and more accurate then trying to check the ID of you seat tube. Calipers are not that
    great at checking internal dimensions. The 3 sizes I see most are 27.2/30.9/31.6 but idk for sure.
    I know there are oddball sizes but I never had an issue with them as of yet.

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