Are all carbons created equally?

Discussion in 'Cycling Equipment' started by saintsfan342000, Apr 10, 2007.

  1. saintsfan342000

    saintsfan342000 New Member

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    I've been doing a lot of research on bikes and the materials involved, and I see a lot of different carbon fibers being used. FACT, monocoque, bontrager, kinesis...are just three that I can think of off the top of my head but you probably know there are many more. Are these all pretty much the same? Or is a cheaper carbon exactly that - cheap? I've been told that a low-end carbon is no better than aluminum. Are carbon seat stays going to make that big a difference if the longest rides I do are ~175 miles? Thanks!
     
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  2. sogood

    sogood New Member

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    There are definite differences just like fabrication of any material. Even stainless steel come in many different grades.

    For CF, there's the fibre, frame design, CF sheet layout design, manufacturing process etc etc to differentiate the good vs the bad.
     
  3. alfeng

    alfeng Well-Known Member

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    Possibly, the easiest way to think about the differences in the various carbon fibers is the weight differences of materials being compared for a given desired strength ... so-called "cheaper" carbon fiber will probably be heavier the way that less exotic-and-less-expensive steel is heavier than the nicer "stuff" that is out there.

    If a frame is made improperly with the best material, then it will probably be a comparatively bad ride when compared to a frame made with a slightly lesser material but with better geometry OR location of the material within the frame's design ...

    Not to be too cynical, but I think the use of carbon fiber REAR stays is as much for marketing as manufacturing expedience ... let's say that it costs the frame manufacturer $75US for each assembly (it could be more, it could be less) ... I'm sure the subsequent frame will carry a $200+ premium over one that was made of a single material, so why wouldn't you provide what the market seems to lust after? The carbon fiber stays on SOME frames can probably be thought of as being MORE like the chrome trim on a 1959 Chevrolet while on other frames it may make a difference ... and, I would think that it actually has greater benefit on a Ti frame to stiffen the rear triangle!?!

    Bling has its place, so it shouldn't be discounted, but reducing the PSI in the rear tire by 5 lbs. from whatever it may be will probably give greater comfort (if comfort is what you are after) than carbon fiber rear stays.
     
  4. p38lightning

    p38lightning New Member

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    Much of what has been said makes good sense to me. I notice that no one has mentioned anything about the resin that is used to solidify the fiber and form the frame. How much of a factor is that in a carbon fiber frame?
     
  5. doctorSpoc

    doctorSpoc New Member

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    This is probably the biggest advancement in carbon fibre frames and parts in the past year is the introduction of carbon nano tubes into the resin which greatly increases the strength to weight ratio of frames

    know BMC uses it...

    nano tubes are microsopic hollow cylinders of carbon... walls are one atom thick... imaging taking chicken wire and forming a cylinder with it.. at each vertex of a hexagon is a carbon atom.. these nano tubes are mixed into the resin for huge gains in strenght.. this is the material that will be used to make next gereration of sky scrapers and has already made it into the next generation of jet fighters...
     
  6. jstock

    jstock New Member

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    Don't know if this is true but to quote the latest issue of Cycling+: "Carbon wishbone back ends simplify large production runs, because it's quicker and easier to bond the moulded wishbone onto the frame than it is to weld aluminum tubes".
    /J
     
  7. Kelderek

    Kelderek New Member

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    "Are all carbons created equally?"

    Absolutely not.
    I can hardly think of any material where you can play with more parameters than with carbon fibre reinforced plastics...

    - The fibre itself comes in different grades (e.g. "high modulus carbon fibre", which means that it is further enhanced by a heat treatment process dusing the manufacturing of the filaments)

    - The quality of the matrix (usually epoxy resin)

    - The layout of the fibre in the matrix (a single carbon fibre does it's magic in one direction only, so the layout pattern is crucial)

    - The process of making the actual frame (an assembly of tubes or a monocoque?)

    - The frame design in itself. Monocoque design leaves the field open to more varied shapes than metal frames, i.e. more opportunities to play with frame geometry, i.e. the span between a good and a bad design increases...

    As you can see, there are actually more opportunities to make a bad carbon frame than a bad metal frame. Likewise, there are more opportunities to make a truly magnificent frame than with any other material!
     
  8. bobbyOCR

    bobbyOCR New Member

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    carbon is carbon, it is an element, end of story, you can't fundamentally change carbon. Carbon fibre isn't the expensive part of building a bike, its the moulds, epoxy, curing technique and joining techniques. The epoxy resin is what gives carbon fibre strength, and is te most important part of a frame. The type of carbon weave also matters. A frame should be built from uni-directional carbon, as all other weaves are cosmetic and add very little stiffness. The gsm of that UD carbon also changes the strength of the frame.

    Some crap chinese carbon rip-offs use fibreglass dyed black.

    Oh yeah, /\/\/\ what he said too (above poster)
     
  9. dhk2

    dhk2 Active Member

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    If you can't fundamentally change carbon, does that mean a diamond and graphite are the same thing? CF can be manufactured in a variety of specs based on tensile strength, modulus of elasticity, spinning of the threads and of course the weave of the final fabrics.

    Also question your statement that the resin is what gives CF strength. After all, the key property of CF is it's amazing tensile strength, which can be several times steel. If this property wasn't important, we could make bike frames out of much-cheaper fiberglass or rayon fabrics, or just mold them out of straight epoxy resin without even bothering with any reinforcements.
     
  10. doctorSpoc

    doctorSpoc New Member

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    it's the strong covalent carbon-carbon bonds, not the resin that gives a carbon fibre frame its strength... the resin just holds the carbon fibers in the correct orientation so the stenght of the carbon fibers can be utillized... it starts as a fabric and is only strong under tension along the fiber.. under compression and forces at any other angle the fiber is pretty useless... saying the stength is in the resin is just wrong.

    edit - carbon nanotubes in the resin mean that less CF is needed since the resin will provide some strength and not in a single direction as the sheets of carbon fiber do.
     
  11. bobbyOCR

    bobbyOCR New Member

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    I'll use this post but epoxy resin is what gives a carbon frame its strength. A good resin that will not deteriorate creates a strong matrix for the fibres. Also, a carbon fibre frame cannot exist without a resin (or other similar substance) to hold it in a fixed position. Whilst carbon fibre has amazing tensile strength, it only utilises that strength if it is being pulled on. Any other direction and it goes floppy and useless. That is why good resin is used to provide some strength in other directions, which is essential.

    "CF can be manufactured in a variety of specs based on tensile strength, modulus of elasticity, spinning of the threads and of course the weave of the final fabrics."

    Yeah, but that isn't changing carbon, that is manufacturing a fibre made from carbon.

    "If you can't fundamentally change carbon, does that mean a diamond and graphite are the same thing?"

    Yeah I know there are covalent networks which form different allotropes but each atom in that network still has 6 protons so, fundamentally, it is still carbon.

    Oh, and what I said was wrong, reading back on it. Carbon fibre is strong without resin, but resin gives a carbon fibre frame integrity (sorry I was tired).
     
  12. Kelderek

    Kelderek New Member

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    Even without the resin matrix, there are differences between various carbon fibres. It's not as easy as "carbon is carbon, period".

    Carbon fibre is 100% carbon, so looking at it on atomic level, it's just carbon. However, carbon fibre is made from oxidation of a so called "precursor", a fibre of a carbon rich material. It's the properties of this fibre, together with the quality of manufacturing process, that will give the carbon fibre it's final properties. The most common precursor is polyacrylonitrile.

    The result is many different qualities of carbon fibre, a distributors website I looked at listed ca 30 different qualities.

    It can be noted that the tensile strength for these 30 or so different qualities varied from 2.75 to 5.94 GPa. This was pure fibre, making a composite out of it with a suitable resin will of course give you further variations in properties and quality.
     
  13. bobbyOCR

    bobbyOCR New Member

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    Cool, that is interesting to know.

    Please note that I said carbon is carbon, it cannot fundamentally changed. Not carbon fibre cannot be fundamentally changed. The title of the thread says (are all carbons created equally) and I am a nit-picker.
     
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