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  1. #1
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    What does it mean to be "monocoque" frame?

    I'm no structural engineer, but I'm under the impression that a monocoque is structure is constructed without fusing tobegher separate "halves".. in other words, the structure is one contiguous piece of fabric

    Is there a truly monocoque frame out there?

    For example, if I look at a Tarmac top tube, I can clearly see a line indicative of 2 piece joining together at the line. I also don't believe the Trek Madone is monocoque frame either (they are lugged underneath all that outter carbon layers).

    Anyway, I'm curious if there is a truly monocoque frame out there in which everything from headtube all the way to the rear triangle.. is constructed as one contiguous piece without any fusing or bonding separate pieces.

    Just curious.

  2. #2
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    Quote Originally Posted by aclinjury View Post
    I'm no structural engineer, but I'm under the impression that a monocoque is structure is constructed without fusing tobegher separate "halves".. in other words, the structure is one contiguous piece of fabric

    Is there a truly monocoque frame out there?

    For example, if I look at a Tarmac top tube, I can clearly see a line indicative of 2 piece joining together at the line. I also don't believe the Trek Madone is monocoque frame either (they are lugged underneath all that outter carbon layers).

    Anyway, I'm curious if there is a truly monocoque frame out there in which everything from headtube all the way to the rear triangle.. is constructed as one contiguous piece without any fusing or bonding separate pieces.

    Just curious.
    There have been various attempts at various "versions" of monocoque over the years. Monocoque means "structural skin" rather than "built all in one piece." But using bladders and a frame mold will allow a one-piece construction. I don't know if there are any of these on the market today and many CF frames use internal lugs and separate tubes. But you can use internal lugs and then mold the frame with bladders and still call it monocoque and not be wrong (though perhaps misleading to the many people who think monocoque means "one piece.")

  3. #3
    'brifter' is a lame word.
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    Quote Originally Posted by aclinjury View Post
    I'm no structural engineer, but I'm under the impression that a monocoque is structure is constructed without fusing tobegher separate "halves".. in other words, the structure is one contiguous piece of fabric

    Is there a truly monocoque frame out there?

    For example, if I look at a Tarmac top tube, I can clearly see a line indicative of 2 piece joining together at the line. I also don't believe the Trek Madone is monocoque frame either (they are lugged underneath all that outter carbon layers).

    Anyway, I'm curious if there is a truly monocoque frame out there in which everything from headtube all the way to the rear triangle.. is constructed as one contiguous piece without any fusing or bonding separate pieces.

    Just curious.
    on the specialized it's most likely a mold line. the trek is definitely NOT lugged under anything. well, i guess they are where the front/rear go together. like most monocoque frames the front triangle is joined to the rear end post-molding. not aware of anything like you're talking about.
    even if the frame was built like you're thinking, there wouldn't be 'one' continuous piece of carbon anywhere that ran front to back. there are so many pieces in a lay-up schedule w/ different fibre orientations it's crazy.
    i work for some bike racers...
    2013 Trek Madone 5.9 w/ '12 SRAM Red
    2010 Cervelo T1 sprint bike
    Ruger 10-22TD
    Smith&Wesson M&P 15-22
    Smith&Wesson M&P 9
    oh, those belong in another forum

  4. #4
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    Quote Originally Posted by cxwrench View Post
    the trek is definitely NOT lugged
    Trek's assembly process is online. Basically all the tubes plug into each other. Excess glue is wiped off and the joint is smoothed over with paint.

    there are so many pieces in a lay-up schedule w/ different fibre orientations it's crazy.
    Some frames could easily have 500 pieces. Trek have a laser cutter to make perfect swatches.

    Moncoque and handmade are so abused they have lost any meaning with regard to bicycles.

  5. #5
    merckxman
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    Were not the Kestrel 200Sc, Sci, 500, of that period (1990s) true monocoque? I still have my 200sci after a zillion miles, can't kill it.

  6. #6
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    Quote Originally Posted by merckxman View Post
    Were not the Kestrel 200Sc, Sci, 500, of that period (1990s) true monocoque? I still have my 200sci after a zillion miles, can't kill it.
    Wasn't the main triangle one piece and the seatstays and chainstays were separate bits added on? They did have chunky stays so maybe it was possible to get a bladder in there.
    A full mono frame could be done but it would be too much bother to be worthwhile IMO.
    I'm glad you're still enjoying your bike, I thought they had a bad rep for failures.

  7. #7
    VKW
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    I'm not an expert in carbon bike frame building but I do work in composites for the defense industry. But if I were to guess, I would think monocoque does not mean one contiguous piece of fabric. I have not seen anything built with one piece of fabric that was structurally strong.

    What I think it means is that the entire frame was laid up as several carbon prepreg plies then molded and cured together as one piece. You might see a seam that is really just resin filling up between the mold halves. The resulting part comes out of the mold as a full one piece frame. There would be no pieces to adhesively bond together. A solid homogenouos carbon layup should in theory be stiffer than tubes and lugs adhesively bonded together at the joints.

  8. #8
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    Quote Originally Posted by VKW View Post
    .....
    ...A solid homogenouos carbon layup should in theory be stiffer than tubes and lugs adhesively bonded together at the joints.
    hmm you made an interesting statement here!

    If the lugs are constructed as thin as the tubings themselves, then you could argue that the lugs (thin) + tubes combination would be weaker than the homogeneous monocoque.

    However, if the lugs are thick, stout, and robust,.. then the lugs + tubes combination will be stronger than the homogeneous monocoque. The shear strength of the glue used in the bonding of lugs + tube is actually stronger than the tubes themselves.

    Serotta, for example, has claimed that their lugs are much stronger than their tubes, and therefore they argue that their frames is stronger than what you would achieve had it been monocoque. The cost of using lugs is usually weight. And I believe lug construction in general is more labor intensive.

    ... or so this is what I have read regarding lugs and monocoque..

  9. #9
    VKW
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    You're right, I can see tube and lug constructions being stronger in that scenario. I was imagining beefed up monocoque joints in comparison to similarly sized lugs.

  10. #10
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    I think in a monocoque, the manufacturers actually do beef up the joints, specifically the headtube and bottom bracket areas. But they can't beef it up to the level of thickness of a lug; if they do, then well then they might as well use lugs (which give them more sizing flexibility). But lugs are expensive.

    Having said this, I've see a cut-away frame of a Fuji carbon bike, which claims to be a "monocoque" frame, and I can say that the headtube area sidewall is "pretty thin".. I mean I can actually pinch the carbon to cause it to flex with my fingers.. certainly no where near as thick as what you get from a lug. Reason why Fuji (and lots of other makers) make their tubes (headtubes, downtubes, toptubes) oversized as to compensate for this wall thinness.

  11. #11
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    Carbon Fiber: Manufacturing - YouTube - how a carbon frame is built

  12. #12
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    Quote Originally Posted by Kerry Irons View Post
    There have been various attempts at various "versions" of monocoque over the years. Monocoque means "structural skin" rather than "built all in one piece." ...
    Pretty much. The term was used to describe aircraft construction long before it was applied to bicycles. In the case of aircraft it meant that the skin carried the structural loads rather than a separate frame, which was often covered in fabric. This permitted lighter more space efficient designs.

    It's kind of an oxymoron for bicycles frames, because a bicycle frame is a frame, so it's not like you're replacing the frame with a stressed skin. I think it's come to mean that the frame isn't constructed of tubes that are joined at the intersection of their axes, but rather that where joints are employed, they occur along the axes. For example, rather than a top tube and a down tube joining at their ends to head tube, a monocoque frame might have a head tube section with long top tube and head tubes stubs with the respective joints occurring more "mid" tube.
    ... 'cuz that's how I roll.

  13. #13
    classiquesklassieker
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    Quote Originally Posted by Cinelli 82220 View Post
    Wasn't the main triangle one piece and the seatstays and chainstays were separate bits added on? They did have chunky stays so maybe it was possible to get a bladder in there.
    A full mono frame could be done but it would be too much bother to be worthwhile IMO.
    I'm glad you're still enjoying your bike, I thought they had a bad rep for failures.
    I think those model lines are considered monocoque, it was the later Kestrel Talon that was made up of the main triangle - seatstays - chainstays pieces.

    For what it's worth, in the road bicycle world, monocoque refers not to the state/nature of the finished frame, but rather the method of construction.

    In its most loose definition, a monocoque frame is simply one that was not constructed by lugged construction, and appear seamless. Lugged construction is done by glue/solder-ing tubes onto lugs.

    Does tube-to-tube construction (used by Cyfac and several others) produce a monocoque frame? :-D

  14. #14
    'brifter' is a lame word.
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    Quote Originally Posted by Cinelli 82220 View Post
    Trek's assembly process is online. Basically all the tubes plug into each other. Excess glue is wiped off and the joint is smoothed over with paint.



    Some frames could easily have 500 pieces. Trek have a laser cutter to make perfect swatches.

    Moncoque and handmade are so abused they have lost any meaning with regard to bicycles.
    not any more. the front end is 'one' piece, and is bonded to the rear end. the old 5000 series Trek frames were bonded oclv tubes and lugs.
    when you think about it, pretty much every carbon frame is handmade. except for the BMC Impec.
    i work for some bike racers...
    2013 Trek Madone 5.9 w/ '12 SRAM Red
    2010 Cervelo T1 sprint bike
    Ruger 10-22TD
    Smith&Wesson M&P 15-22
    Smith&Wesson M&P 9
    oh, those belong in another forum

  15. #15
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    Quote Originally Posted by cxwrench View Post
    ....... except for the BMC Impec.
    ???????

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    so what I'm getting from reading you guys so far is that, "monocoque" has more meaning for the industry (aerospace) in which the term was coined, but when used and thrown around in the bicycle industry, it serves more to stir up hype, marketing, and misinformation than actual knowledge?

    And another thing that's baffling to me. To me, a "frame" of a bicycle should be thought of as complete front and rear triangle. Yet, a monocoque frame they're refering to just refers to the front triangle. But don't the chain stays hold the other "endpoint" (the rear wheel axle) of a bicycle, and therefore, do play a crucial role in transferring power from crank to rear wheel? You can have the stiffest monocoque front triangle all you want, but if the bicycle is noodly anywhere from the bottom bracket to the rear dropouts, or anywhere along the the chain stays, then all that stiffness won't mean didley squat.

  17. #17
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    My Tarmac claims to have a triple moncoque frame. If one monocoque is good, then three of them must be three times as good!
    Old La Honda in less than 20 minutes! Or you can watch race video from the low-key hill climb on Welch Creek. More at www.biketelemetry.com.

    "I think," said Christopher Robin, "that we ought to eat all our Provisions now, so that we shan't have so much to carry.", Winnie-the-Pooh, A. A. Milne.

  18. #18
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    Monocoque - Wikipedia, the free encyclopedia

    "monocoque" is perfectly acceptable to use in reference to a carbon bicycle frame.

  19. #19
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    The Impec is made of machine made CF tubes joined by lugs. It is mostly made by a computer controlled machine. It's pretty slick engineering.

    IMO, tube-to-tube construction (Sarto, Cyfac, Guru, etc.) is not considered monocoque.

  20. #20
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    Monocoque is a construction technique that utilises the external skin to support some or most of the load. This is as opposed to using an internal frame or chassis that is then covered with cosmetic body panels.


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    Last edited by kathy20052012; 01-28-2013 at 11:03 PM.

  21. #21
    'brifter' is a lame word.
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    Quote Originally Posted by kathy20052012 View Post
    Monocoque is a construction technique that utilises the external skin to support some or most of the load. This is as opposed to using an internal frame or chassis that is then covered with cosmetic body panels.
    i'm guessing you're a race car person, yeah?
    i work for some bike racers...
    2013 Trek Madone 5.9 w/ '12 SRAM Red
    2010 Cervelo T1 sprint bike
    Ruger 10-22TD
    Smith&Wesson M&P 15-22
    Smith&Wesson M&P 9
    oh, those belong in another forum

  22. #22
    wim
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    Quote Originally Posted by kathy20052012 View Post
    Monocoque is a construction technique that utilises the external skin to support some or most of the load. This is as opposed to using an internal frame or chassis that is then covered with cosmetic body panels.
    Precisely right. Of course and as said by others, you could apply this engineering definition to all carbon fiber reinforced plastic (CFRP) bicycle frames. What makes discussions like these contentious is the fact that the bicycle marketeers have taken the term "monocoque" and made it mean whatever they want it to mean. But this sits square in the tradition of bicycling advertising copy: lots of bunk masquerading as engineering or science.

  23. #23
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    Quote Originally Posted by JoelS View Post
    The Impec is made of machine made CF tubes joined by lugs. It is mostly made by a computer controlled machine. It's pretty slick engineering.

    IMO, tube-to-tube construction (Sarto, Cyfac, Guru, etc.) is not considered monocoque.
    The same as Look and Time were doing ten years ago?

  24. #24
    classiquesklassieker
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    Quote Originally Posted by ewitz View Post
    The same as Look and Time were doing ten years ago?
    Are you referring to the Impec/BMC method or the tube-to-tube? LOOK and TIME were doing lugged construction until a few years ago, they started with lugs and tubes, which are then joined/bonded.

    TIME advertised that their tubes were made in-house. But as far as I can tell they still start with lugs and tubes.

    And if I understand the BMC/Impec method, they start with tubes, put them on a jig, and then weave/build lugs around exactly how the tubes are supposed to be supported.

  25. #25
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    Quote Originally Posted by orange_julius View Post
    Are you referring to the Impec/BMC method or the tube-to-tube? LOOK and TIME were doing lugged construction until a few years ago, they started with lugs and tubes, which are then joined/bonded.

    TIME advertised that their tubes were made in-house. But as far as I can tell they still start with lugs and tubes.

    And if I understand the BMC/Impec method, they start with tubes, put them on a jig, and then weave/build lugs around exactly how the tubes are supposed to be supported.
    I'm wondering what's the advantage of building the Impec like they do (if what you said is true). Why put lugs in a jig and build lugs around them? Surely lugs can be built outside of a jig if the correct specifications are given. I wonder if it's easier or harder to build a lug around a tubeset set in a jig. Is there something about this building technique that gives the frame any advantage over the traditional lug method?

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