Results 1 to 13 of 13
  1. #1
    mtbr member
    Reputation: tailwaters's Avatar
    Join Date
    May 2007
    Posts
    839

    Carbon Seat Post

    Just purchased a Hylix carbon seat post with off-set in 400mm for my new Niner EMD. I installed it last night and it looks great however I noticed this thing has a fair amount of flex. I've never run carbon before so this makes me a bit nervous. Is this typical out of a carbon seat post?

  2. #2
    mtbr member
    Reputation: IndianaXC's Avatar
    Join Date
    Jun 2011
    Posts
    115
    Yes, thats the whole reason to run a carbon post since i makes for a slightly more forgiving ride.
    Giant XTC Composite 29er, SID XX World Cup fork, AC Race 29 wheels
    Giant TCR advanced with Ultegra Di2

  3. #3
    mtbr member
    Reputation:
    Join Date
    May 2005
    Posts
    823
    IMO, flex is good, assuming it's designed that way. I've been using carbon windsurfing masts for 15 years and they deflect a lot under load, sometimes 30+ deg. and usually last a long time

    Can you post some pics of the post? The one's on eBay are not very good.

  4. #4
    Sweep the leg!
    Reputation: Caffeine Powered's Avatar
    Join Date
    Mar 2005
    Posts
    3,824
    Don't know about yours, but my Bontrager ACC has an aluminum core. It does flex, but it won't snap as easily.
    Authorities speculate that speed may have been a factor. They are also holding gravity and inertia for questioning.

  5. #5
    fresh fish in stock...... SuperModerator
    Reputation: CHUM's Avatar
    Join Date
    Aug 2004
    Posts
    8,291
    that's because it's not 29'er infused carpet fiber

    moved to general

    Visit these 2 places to help advance trail access:
    http://www.sharingthepct.org/
    http://www.facebook.com/SharingThePct

  6. #6
    MTC rep for LPCPCAC
    Reputation: bankerboy's Avatar
    Join Date
    Oct 2006
    Posts
    1,117
    Got the popcorn ready for the inevitable carbon debate....

    Carbon, fantastic light weight and strong or are we completely fooled by the industry trying to sell us inferior product so they can make a buck?
    Apathy will get you exactly what you deserve

  7. #7
    mtbr member
    Reputation:
    Join Date
    Dec 2011
    Posts
    34
    running the 9er carbon post and it flexes somewhat but not as much as the RDO. I like it so far

  8. #8
    mtbr member
    Reputation:
    Join Date
    Oct 2007
    Posts
    940
    Engineering wise carbon fiber is a poor material choice for seats posts. Here is why. Carbon Fiber is designed to work under tension. Don't believe me, have you ever tried to push on a rope? It doesn't work. So the next question is why do companies build seat posts out of carbon fiber? Mainly because of the cool factor and some will argue because it provides a more compliant comfortable ride.

    Since all seat posts are under what engineers call "Buckling loads." lets look at the equation for buckling.

    Buckling - Wikipedia, the free encyclopedia

    Critical Force= (pie*pie*modulas of elasticity*aera moment of inertia) / (load factor*length)^2


    So looking at the equation here is what we need to do in order to maximize how much load our seat post can take before it fails.

    1)We want to maximize the modulas of elesaticity by selecting the proper material.

    2)We want to maximize the area moment of inertia, this means using the largest diameter seatpost we can get and using the thinest allowable wall thickness.

    3)We want to keep the seat post as short as possible as length is a squared term. (very bad!)

    Understanding that you can now understand why LJ Thompson makes the bench mark seatpost in the bicycle industry. Thompson has done a lot of engineering work to optimize the cross sectional area (moment area of inertia) of the seat mast.



    As you can see Thompson puts more material where the greatest stresses are in the seat post which is in the front of and the back of the seat mast. Since the sides of the seat mast see the least amount of stress the side walls are left thinner.

  9. #9
    mtbr member
    Reputation: Brewtality's Avatar
    Join Date
    Jul 2007
    Posts
    5,632
    Quote Originally Posted by Fortuitous View Post
    None of my carbon posts failed, but one of my Thompson posts did. If only they put more material on the sides...
    That pic appears to show abrasion and impact damage to your seatpost.
    Thats not a failure of the seatpost per se. Most likely any seatpost would have dented in that situation, regardless of the design or construction material.
    Its all Shits and Giggles until somebody Giggles and Shits

  10. #10
    mtbr member
    Reputation: Brewtality's Avatar
    Join Date
    Jul 2007
    Posts
    5,632
    Quote Originally Posted by Fortuitous View Post
    Just a routine impact.
    I don't consider any impact as 'routine'.
    Its all Shits and Giggles until somebody Giggles and Shits

  11. #11
    mtbr member
    Reputation: tailwaters's Avatar
    Join Date
    May 2007
    Posts
    839
    Well the seat post in question was in fact purchased on ebay and came from overseas. Here's a pic. I've read some good reviews on their products but like I said this is my first carbon seat post and the flex is a new thing to me. The model I purchased is the offset model but same brand.
    Attached Thumbnails Attached Thumbnails Carbon Seat Post-hy-02-2-.jpg  


  12. #12
    mtbr member
    Reputation:
    Join Date
    Feb 2011
    Posts
    88



    Actually the Hylix carbon post has this same feature. I got one a few weeks ago and havent had a chance to ride it yet so cant comment on the durability or flexibility issues...

  13. #13
    mtbr member
    Reputation:
    Join Date
    Oct 2007
    Posts
    940
    Unless your bicycle came orginally with a carbon seat post I don't recommend using them. In fact most bicycle component manufacters are slowly moving away from them.

Similar Threads

  1. DIY/Ghetto Adjustable Seat Post
    By DirtyMartini in forum General Discussion
    Replies: 13
    Last Post: 05-02-2012, 05:17 AM
  2. Grip glue for slipping seat post on carbon frame?
    By Will Goes Boing in forum General Discussion
    Replies: 4
    Last Post: 11-11-2011, 10:33 AM
  3. Rush Carbon seat post clamp
    By ASI CA in forum Cannondale
    Replies: 5
    Last Post: 05-20-2010, 09:40 AM
  4. Scratched - Carbon Seat Post
    By Norco1982 in forum All Mountain
    Replies: 18
    Last Post: 10-26-2009, 08:10 PM
  5. Carbon SEAT post? Crazy
    By BigDaddyJT in forum Clydesdales/Tall Riders
    Replies: 12
    Last Post: 11-08-2004, 04:29 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •