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Carbon properties and qualities advice - HM v 3k

chris217chris217 Posts: 217
edited November 2010 in Road buying advice
at a risk of over simplifying, i am looking for some understanding of the properties of certain carbon.

for example High Modulus carbon i am assuming is perhaps a 'higher quality' than 3k and therfore ride quality will be better ?

i am aware tere is also the weave to take into account. 12k stiffer / harsh ?? 3k more forgiving ??

is there a carbon hierarchy as such ?

any help cheers

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  • jnr_hjnr_h Posts: 18
    Roughly: Standard modulus, (Intermediate Modulus), High Modulus and Ultra High modulus.
    These refer to the stiffness of the carbon.
    If you were to build three identical frames, using identical lay-ups from the same tool, but different modulus cloths, they would weigh the same but the UHM frame would be stiffer than the HM frame which in turn would be stiffer than the SM frame.
    The frame designer can thus use less UHM carbon to make an equivalent stiffness, but lighter frame than one made from SM carbon, or one that is the same weight but stiffer, or somewhere in between.

    The ride quality will largely be dependant on the geometry of the frame (and tubes) as well as the stiffness designed into the tubes by the layup used.

    The cloth types are varied according to location and use. (Both manufacturing and end product considerations). For instance twill would be used on a surface which is going to be cut or drilled because it will not come apart around the cut/drilled edge like a ud cloth and it will be more resistant to wear on that surface.

    Try Gurit site - Gurit guide to composites.
  • Carbon fibre is such a lightweight material that differences in weight are barely perceptible. Make the 'same' frame from HM and SM fibres, and in theory you could make the HM frame a tiny bit lighter.

    But in terms of bike frames, theory does not translate to practice. CF frames are now being 'overdesigned' as it were: bottom brackets are becoming hugely oversized and frames are incorporating aerodynamic features. Frame designers are increasingly viewing CF as a material that can be used with very little weight penalty, and this is especially the case on account of the UCI weight limit.
  • geebee2geebee2 Posts: 248
    for example High Modulus carbon i am assuming is perhaps a 'higher quality' than 3k and therfore ride quality will be better ?

    i am aware tere is also the weave to take into account. 12k stiffer / harsh ?? 3k more forgiving ??

    Err, 12k and 3k are weaves, which are mainly cosmetic, but can make a small difference to stiffness, see

    http://www.storckbicycle.com/usa/index. ... arbonfiber

    "High modulus" refers to the strength of the carbon fibre.
    It's bloomin strong :)
  • chris217chris217 Posts: 217
    thanks guys, so in theory would a high level carbon frame be more likely to have higher modulus CF ??

    slightly rhetorical but am i right in thinking higher modulus = higher strength therefore less material required therefore lower weight ?

    what about ride quality ? i appreciate the geo and design is more likely to impact upon ride characteristics ...but assume the actual CF used will surely have an impact

    mentioning no names but you can get pretty cheap CF frames that are light but quite 'wooden' and not inspiring or comfortable
  • jnr_hjnr_h Posts: 18
    chris217 wrote:
    thanks guys, so in theory would a high level carbon frame be more likely to have higher modulus CF ??

    Yes, but as Berk B said, the weight differences are very tiny - trimming some length out of a few layers has a negligible weight gain.

    The way a manufacturer makes a cheap frame is by using an unrefined laminate - ie less local reinforcements/changing ply extents in the layup process - it is cheaper to do this because it is faster to build. Less labour. A top end frame has stiffness built into the right areas like the bb.
    There is a large cost implication for using higher modulus cloths. Also, the modulus refers to the stiffness, not the strength of the material (although in practise, higher mod carbon usually has a slightly higher ultimate strength as well).
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