How tight for a stem on an alloy/Carbon wrap handlebar?

cleeve hill reject
cleeve hill reject Posts: 426
edited June 2009 in Workshop
I have recently fitted and alloy/carbon wrap handlebar to my bike and a new alloy stem. Unfortunately a creak has developed in that area. I was wondering how tight such a stem on such a setup should be done up, I was thinking tight seeing as the carbon won't be crused with an alloy tube inside it, but I don't want to crank up the tension if it might damage it! I have also put in an extra spacer under the stem, maybe this might be the cause of it? Any ideas/solutions, the bar doesn not seem to be slipping but the creak is annoying me whenever I'm climbing or putting pressure through the bars!

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Comments

  • Slow Downcp
    Slow Downcp Posts: 3,041
    Did you grease the bolts, and the interface between stem and bars? Quite often a dry joint is the problem.
    Carlsberg don't make cycle clothing, but if they did it would probably still not be as good as Assos
  • Will greasing the stem/bar interface not make it slip? What sort of grease should I be using on the carbon, I know some are not recomended?

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  • Slow Downcp
    Slow Downcp Posts: 3,041
    I've always put a very thin smear of grease on the joint. If you don't want to use grease on the carbon wrap, get some carbon seatpost compound.
    Carlsberg don't make cycle clothing, but if they did it would probably still not be as good as Assos
  • Sounds like a good idea, I'll give it a try. 4000 feet of climbing on Dartmoor today was very trying with a creaking stem!

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  • I have recently fitted and alloy/carbon wrap handlebar to my bike and a new alloy stem. Unfortunately a creak has developed in that area. I was wondering how tight such a stem on such a setup should be done up, I was thinking tight seeing as the carbon won't be crused with an alloy tube inside it, but I don't want to crank up the tension if it might damage it! I have also put in an extra spacer under the stem, maybe this might be the cause of it? Any ideas/solutions, the bar doesn not seem to be slipping but the creak is annoying me whenever I'm climbing or putting pressure through the bars!

    With carbon, a material that's very strong in tension, but very weak in compression, you really should always use a torque wrench. I have seen alot of carbon bikes that have been damaged soley due to over tightening - remember thatr carbon fibre works in tension only - not in compression. The damage can cause small cracks and that could be why it's creaking.

    Creaks on a carbon frame mean 'investigate further' (another reason I like steel!!!).

    (PS If you come from Cleeve Hill, I wouldn't ride it down Stockwell Lane until you've sorted it out!!)
    BTP,

    Perth, WA
  • 'dude's right.
    with carbon,you gotta use a torque wrench.
    any carbon,anywhere
  • You could try this or this

    It's a high friction 'grease' designed for assembly of carbon bike parts. It doesn't affect the carbon, reduces the amount of torque required, doesn't scratch and prevents creaks. Used it on my seatpost and it seems to work nicely.
    It doesn't get any easier, but I don't appear to be getting any faster.
  • andy_wrx
    andy_wrx Posts: 3,396
    With carbon, a material that's very strong in tension, but very weak in compression, you really should always use a torque wrench. I have seen alot of carbon bikes that have been damaged soley due to over tightening - remember thatr carbon fibre works in tension only - not in compression. The damage can cause small cracks and that could be why it's creaking.

    But it's not carbon, he said it's 'carbon wrap', so what we're talking about is a thin skin of carbon-fibre reinforced plastic over an aluminium-alloy tube.

    The strength in compression will derive mainly from the thickness and metallurgy of that bit of aluminium inside...

    If it's a high-end, high-tech, expensive carbon-wrap bar, it could be that it's very thin-wall alu working in conjunction with the carbon layer and getting its strength and resilience from both materials working together
    - in which case, you'd have to be careful not to over-torque it up, just as you would with a thin-wall alu bar because you'd crush it and cause it to fail, or with a carbon bar where you'd crack it and cause it to fail.

    On the other hand, if it's just a cosmetic job - a veneer of carbon-wrap over a tough-as-old-boots thick alu bar, you'll get away with a lot more with it...
  • andy_wrx wrote:
    But it's not carbon, he said it's 'carbon wrap', so what we're talking about is a thin skin of carbon-fibre reinforced plastic over an aluminium-alloy tube.

    The strength in compression will derive mainly from the thickness and metallurgy of that bit of aluminium inside...

    Yes, you are right - I didn't see the 'wrap' bit.

    Carbon wrapped around aluminium is a composite. However, the point of wrapping carbon around aluminium is what..? To gain strength by reducing weight, right?. In which case, it the carbon does fail due to compression you are left with the strength of aluminium, which is probably inadequate. If it was strong enough in the first place, then why did they bother wrapping carbon around it?

    It's not for stiffness. The torsional stiffness of a tube depends, more than anything, on its diameter.

    In today's modern bike market, weight (or rather lack of weight) sells. To get the lightest weights possible, manufacturers trim tube thicknesses accordingly. And that is why nearly all fixings on modern bikes require a torque setting.

    My local frame builder has stopped building frames. He now makes a very good living repairing carbon. Whilst many of the frames that come in are damaged, some are inadequate due to poor engineering design. Most are damaged because the shop bike 'mechanic' overtightened them.

    Why would you spend alot of money on a bike and not follow the recommended maintenance procedures???
    BTP,

    Perth, WA
  • andy_wrx
    andy_wrx Posts: 3,396
    However, the point of wrapping carbon around aluminium is what..? To gain strength by reducing weight, right?.
    If it was strong enough in the first place, then why did they bother wrapping carbon around it?

    Maybe - but another common reason for doing it is cosmetic/vanity, plain old fashioned marketing !

    There are lots of bars, seatposts, even tennis rackets, out there which are sold as 'carbon' but are in fact carbon wrap over aluminium : these are heavier than plain old aluminium, no stronger, no more buzz-absorbent, etc.

    They sell, because people want 'carbon' bling.

    Notice how I separated them into 'high-end, high-tech' carbon wrap bars and 'cosmetic jobs'...
  • andy_wrx wrote:
    However, the point of wrapping carbon around aluminium is what..? To gain strength by reducing weight, right?.
    If it was strong enough in the first place, then why did they bother wrapping carbon around it?

    Maybe - but another common reason for doing it is cosmetic/vanity, plain old fashioned marketing !

    There are lots of bars, seatposts, even tennis rackets, out there which are sold as 'carbon' but are in fact carbon wrap over aluminium : these are heavier than plain old aluminium, no stronger, no more buzz-absorbent, etc.

    They sell, because people want 'carbon' bling.

    Notice how I separated them into 'high-end, high-tech' carbon wrap bars and 'cosmetic jobs'...

    At the risk of sounding likne an old Luddite, I think I'll stick with my steel frame :)
    BTP,

    Perth, WA