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How tight? Carbon seatpost. No torque gauge.

Discussion in 'Bicycle Mechanics and Repairs' started by stevenb, 26 Sep 2007.

  1. stevenb

    stevenb New Member

    Location:
    South Beds.
    How tight should I tighten my seat post clamp in terms of using my hand to judge...i have no torque gauge to measure.
    I have a Carbon fibre post going into an ally seatpost on my felt bike.
    I don't want to damage the carbon post.
    I have tightened it fairly tight.....but not to the point where I'm grimmacing with effort...no where near that tight.
    i know that ultimately it should be just tight enough so that it doesn't slip....but i don't want to keep it loose and have it slip down while I'm riding.

    Cheers for any help.

    Steve
     
  2. stevenb

    stevenb New Member

    Location:
    South Beds.
    I meant to put this in the KNOW HOW section...:whoops:

    Cheers for moving this guys. xx(
     
  3. Stwutter

    Stwutter New Member

    Without a torque gauage or wrench, you do have to rely on the 'feel'.

    Personally, the first thing I do is tighten it just enough so it doesn't move, and then turn it using just light-ish grip (like just using the ends of your fingers and thumb) until it stops turning, and no more. That's usually plenty. I do this 'cos I used to tighten everything so much that my middle name was 'threaded'.

    Oh, and, just as an after-thought, don't grease a carbon seatpost - you'll never get the bloody thing out again.
     
  4. I have a carbon post in a carbon frame and had a similar dilemma, the post slipped even though I was tightening the clamp beyond the point I felt comfortable and certainly a bit more than the maximum torque stated on a sticker on the frame.

    The solution was Tacx carbon assembly compound.
    It's not grease, in that it's water-based rather than oil-based, so it won't chemically attack your seatpost, but it contains lots of tiny glass-fibre balls which act to grip the post.

    You can buy a pot of it for a tenner, or ProbikeKit sell a smaller 'syringe' of the stuff for £3.99 or so
     
  5. stevenb

    stevenb New Member

    Location:
    South Beds.
    Whoops...I put grease on my post last night.
    I will clean it off tonight and wipe the inside of the frame dry with alcohol spray.
    Thanks for the good advice chaps.
    Steve
     
  6. rob_mcp

    rob_mcp New Member

    as far as torque goes I discovered that I needed about 8 to 10 lbft on my carbon trek with carbon seat post. Now 8 lb ft is 16 lb 6" and the bike weighs about 16lb, so I go t my alen key socket on a bar and held it 6" from the alen key, put this in the seat clamp and lifted the bikeup with it - a bit heath robinson but it did the trick for me.

    Incidentally I have since got a low range torque wrench and have always found that I haven't been doing things up as tight as I should according to hte manufacturers recomendataions
     
  7. Globalti

    Globalti Legendary Member

    Experienced engineers know how far to tighten bolts by having a feel for the elasticity of the metal.
     
  8. giant man

    giant man New Member

    Location:
    Essex innit?
    But not everyone's an experienced engineer Rigid Raider!
     
  9. monnet

    monnet Über Member

    I always mark up the start point of my turns when I loosen anything carbon related. ie: a marker pen across the nut/screw head and onto the sleeve. Then when I undo it I count how many turns it takes to get whatever it is loose. When it comes to tightening everything back up all that needs to be done is to count the turns back in and the lines should match up as proof that you're back where you started. Of course if you're fitting a new seat post then you might have to rely a bit on feel too.
     
  10. stevenb

    stevenb New Member

    Location:
    South Beds.
    Good idea that....:biggrin:
    Carbon cannot be treated like metal and as such it is well worth checking the required torque settings.
    I'm not an experienced bike mechainc...although competent enough.....so I think I will familiarise myself with my bike and then adopt methods like you have mentioned Monnet. :biggrin:
     
  11. I've never had a problem with my Sirrus (alu frame) and carbon post, touch wood. But with my Bianchi (Carbon frame & Post), the post slips. On the seat clamp there is a little Arrow it points to nothing at first but as you tighten the clamp it moves towards "carbo" there's a further mark "classic" but I've never went that far. Am I correct in thinking thats a gauge of some sort?
    2073850971_b8710f1d8c.jpg
     
  12. Smokin Joe

    Smokin Joe Legendary Member

    It looks like a gauge, and a good idea too. For those who are unsure if they are overtightening their carbon seatpost it is worth taking it out to check. I overtightened my first one and did not realise until I fitted a new saddle and needed to raise the post. I found it had cracked just below the level of the seat tube, I don't know how far off a nasty accident I was but it was definately on the way to failing.
     
  13. NickM

    NickM Über Member

    Ah - what Mike Burrows calls "gritty grease" :biggrin:

    So Tacx do make something useful, after all.

    An alternative, which worked well for me, is maximum-hold hair spray. You can mask off the bit of the seatpin which is outside the frame and apply more than one coat if needed.
     
  14. Cyclist33

    Cyclist33 Guest

    Location:
    Warrington
    oo-er. i just bought a new carbon seatpost. it had no markings on at all, ie no paintwork nor weave work. i fitted it and tightened my clamp yesterday, i didnt go absolutely nuts but did it pretty snug, no gauge, and now there is kind of like what looks like a long linear internal "bruise" along the length of the post facing the rear. i got it out and have looked at the base rim of the post and it looks sound so having very little experience of carbon, is this just a normal bit of resin popping out or have i gone and truly stuffed it up?

    thing is, it wouldnt stay still otherwise.

    stu
     
  15. Cyclist33

    Cyclist33 Guest

    Location:
    Warrington
    okay so just released the post and then tightened it bit by bit a quarter turn at a time, checking for movement each time. its now as non-tight as it will go and stay secure. does feel pretty tight. guess i have no choice.