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  1. #1
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    quick seat post size question 30.8 okay for 30.9?

    Hey guys, just got a new Stumpjumper FSR.
    friggin' LOVE this bike... so plush.

    been riding it for a few weeks now, but am experiencing some elbow pain, and think I've tracked it to fit and posture; I'm reaching too far forward so my tendency is to lock my elbows on the trail.

    anyway, putting on a shorter stem, but also want to switch to a setback seatpost to adjust my position over the cranks.

    spec on the bike says 30.9mm for the seatpost. can I get away with a 30.8mm though?
    I mean, seriously, 1/10th of a mm?

  2. #2
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    the diameter of the post is 30.9, not the setbck. i think the setback is 12mm? get a thomson setback, although i dont think it has much more mm set back than the spesh, it just looks that way.

  3. #3
    Stray Bullet
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    Is ruining your frame worth $40?

  4. #4
    Calm Like a Bomb
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    no, u definitely need the right size seat post...u could get some seat post shims but it's not recommended...just get the right post size
    Carbon Wilson
    Carbon Troy

  5. #5
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    Show me who makes a 30.8 seatpost? I want to see this.

  6. #6
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    Carbon Wilson
    Carbon Troy

  7. #7
    Big Gulps, Alright!
    Reputation: Berkley's Avatar
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    .1mm is enough to ovalize a headtube. Similarly, a seat tube...

  8. #8
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    Even a 30.9 is a loose fit in my Stumpjumper Fsr, so I certainly would not go with even a smaller diameter.

  9. #9
    I AM I AM
    Reputation: ducktape's Avatar
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    Syncros also makes 30.9.
    I would get the right size. If you got the 30.8 no guarantee it will be exactly 30.8 anyway, depends what tolerances they engineer it to.
    A post that won't stay in position without huge torque is just no fun at all!

  10. #10
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    thanks for the informative posts, guys -- this is just what I was looking for; especially the ones that weren't just post count building one liners, devoid of any meaningful information.

    just did a little math yesterday afternoon to see the actual diff. in area and circumference. 0.1mm doesn't seem like much, but seeing the difference on paper... maybe on a steel frame it wouldn't be that big of a deal, but you're right, I won't risk it with an aluminum seat tube.

    I was wondering at first if maybe it was a typo on the sites I was looking at; haven't been parts shopping in a long while, and I had no idea there are so many different sizes, however close they may seem.

  11. #11
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    Quote Originally Posted by Trevorken
    Even a 30.9 is a loose fit in my Stumpjumper Fsr, so I certainly would not go with even a smaller diameter.
    get yourself a salsa clamp. fixed all my loose post issues....

  12. #12
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    I don't have a problem with the clamp (I use a Tune Wurger)
    What I meant was that if I loosen the clamp, the seatpost directly drops down.
    My Stumpjumper Fsr of 2001 was a lot tighter with the same seat post.

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