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  1. #1
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    Past Minimum Insertion on Seatpost

    An old mountain bike is past minimum insertion on the seatpost by about an inch when I put the saddle high enough.

    The post measures 1.064" (27.0 mm) and extends about 8" out of the frame.

    I had no lock searching here or finding a longer seatpost. Or, figuring out what to order anyway.

    Could someone please explain how seatpost measurements work?

  2. #2
    Senior Member joeprim's Avatar
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    I don't know how the measurements work, but pulling that much too much out is asking for trouble. Did you look at Nashbar and the other on line sites for a longer seat post?
    luck

  3. #3
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    Check Price Point, too. But before you do that, read the side of the seatpost to find out your size.

    8" post? That's about 400mm, good luck finding one appreciably longer...........

  4. #4
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    I'm not sure how these are measured. The post says 27.2 mm dia.

    From the rails to the end of the post is 11-3/4", or 300 mm. The minimum insertion mark to the end is 4". I would have 3", which I agree is asking for trouble.

  5. #5
    Cycle Year Round CB HI's Avatar
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    Google or call the LBSs for "27.2 x 400 mm seatpost".
    Land of the Free, Because of the Brave.

  6. #6
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    They make 27.2 x 350 and 400mm seatposts. Time for a new seatpost.

  7. #7
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    So . . . 350 mm or 400 mm . . . how is that measured? Is that the total length of the post?

  8. #8
    rebmeM roineS JanMM's Avatar
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    You measured 300mm - that's one of the standard sizes. The next size larger from what you have should be just right for you. 350-400, as suggested previously.

    Seat post length is measured "from the bottom of the post to centerline of the seat rails." I seen that on the internet.
    RANS V3 (steel), RANS V-Rex, RANS Screamer

  9. #9
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    Thanks guys. Off to da bike store . . .

  10. #10
    Senior Member Nermal's Avatar
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    Quote Originally Posted by DX-MAN View Post
    Check Price Point, too. But before you do that, read the side of the seatpost to find out your size.

    8" post? That's about 400mm, good luck finding one appreciably longer...........
    Just in case it becomes important to the OP or anyone else, 8" is nowhere close to 400mm. 8" is almost exactly 200mm. 400mm is about 15 3/4". I did it the easy way and pulled out the old English/metric tape measure. Makes a really dandy rough calculator.
    Some people are like a Slinky ... not really good for anything, but you still can't help but smile when you shove them down the stairs.

  11. #11
    Senior Member wahoonc's Avatar
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    I might pull a seat post a 1/4"-1/2" past the minimum mark, but no more and I would rather not. Depending on the type of bike, strength/weight of the rider and the frame composition even that small amount could be too much. Get a longer seat post.

    Aaron
    Webshots is bailing out, if you find any of my posts with corrupt picture files and want to see them corrected please let me know. :(

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  12. #12
    Humvee of bikes =Worksman Nightshade's Avatar
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    For safety's sake long seat post should start to lean towards solid bar stock rather than tubing.

    I know, I've just been down that road.

    Rode out, walked back with a bent seat post.
    My preferred bicycle brand is.......WORKSMAN CYCLES
    I dislike clipless pedals on any city bike since I feel they are unsafe.

    Originally Posted by krazygluon
    Steel: nearly a thousand years of metallurgical development
    Aluminum: barely a hundred, which one would you rather have under your butt at 30mph?

  13. #13
    ... Brittain's Avatar
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    I just noticed last week that I've been riding for over two years with my seat post almost an inch beyond the minimum insertion point. Maybe I should think of getting a longer seat tube?

  14. #14
    coprolite fietsbob's Avatar
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    People have broken off the end of the frame's , seat-tube, by riding with the post
    up past the max height line..

    it needs to extend into the frame past the lower side of the top tube join.

    I found a proper diameter 2 bolt Campag seat post,
    but it was to be to far extended, when I built my sloping top tube touring frame.

    solution was buy a similar OD Kalloy post, have the OD and ID
    of the 22.2 end of the post machined , sleeved to fit together,
    then welded together, and machined the aluminum bead back down
    to the same OD of the rest of the seat post..

    2 bolt Campag seat posts and brooks leather 2 rail saddles
    are made for each other.

  15. #15
    DON'T PANIC!
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    Quote Originally Posted by Nightshade View Post
    For safety's sake long seat post should start to lean towards solid bar stock rather than tubing.

    I know, I've just been down that road.

    Rode out, walked back with a bent seat post.
    http://physics.stackexchange.com/que...ar-of-same-o-d

    A hollow tube will have nearly all of the strength of a solid bar for a fraction of the weight. The fact that you bent one probably has to do with how it was damaged or a manufacturing defect.
    Weight (April 2010) 200lb -> Goal (Nov 2010) 145lb Achieved -> (Aug 2011) 132lb 10%BF

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  16. #16
    coprolite fietsbob's Avatar
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    The post measures 1.064" (27.0 mm) and extends about 8" out of the frame.
    Have used a Chrome Moly steel tube seatpost , with 12 of its 18 inch length sticking up.

    SBS/ Red Line makes them available, 1" OD, a machined shim with the 25.4mm ID
    and the proper OD to match the inside diameter of the Frame's seat tube
    is available , so the solution to the OP's situation is just a trip to the Bike Shop.

  17. #17
    Humvee of bikes =Worksman Nightshade's Avatar
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    Quote Originally Posted by Brontide View Post
    http://physics.stackexchange.com/que...ar-of-same-o-d

    A hollow tube will have nearly all of the strength of a solid bar for a fraction of the weight. The fact that you bent one probably has to do with how it was damaged or a manufacturing defect.
    True to a point. What is unknown here is.......the riders weight, riders riding style (rough or easy), how long outside of frame etc.

    That said, tube wall thickness also plays a huge role in tube strength. Most cycle stuff is thin wall tubing so it really isn't all that strong.

    I'm a BIG fella so in order to get a safe solid seat post for my Cruiser I went to a solid 7/8" stainless steel bar stock post. It will not bend under my weight.

    Sure I know that a bar stock post is sinful heavy but it's a choice....ride safe or ride with a post that might bend or break poking you know where!!
    My preferred bicycle brand is.......WORKSMAN CYCLES
    I dislike clipless pedals on any city bike since I feel they are unsafe.

    Originally Posted by krazygluon
    Steel: nearly a thousand years of metallurgical development
    Aluminum: barely a hundred, which one would you rather have under your butt at 30mph?

  18. #18
    Senior Member wahoonc's Avatar
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    I don't worry about the seat post breaking I worry more about the frame on the bike splitting out.

    Aaron
    Webshots is bailing out, if you find any of my posts with corrupt picture files and want to see them corrected please let me know. :(

    ISO: A late 1980's Giant Iguana MTB frameset (or complete bike) 23" Red with yellow graphics.

    "Cycling should be a way of life, not a hobby.
    RIDE, YOU FOOL, RIDE!"
    _Nicodemus

    "Steel: nearly a thousand years of metallurgical development
    Aluminum: barely a hundred
    Which one would you rather have under your butt at 30mph?"
    _krazygluon

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