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



## aclinjury (Sep 12, 2011)

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.


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## Kerry Irons (Feb 25, 2002)

aclinjury said:


> 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?
> 
> ...


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.")


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## cxwrench (Nov 9, 2004)

aclinjury said:


> 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?
> 
> ...


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.


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## Cinelli 82220 (Dec 2, 2010)

cxwrench said:


> 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.


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## merckxman (Jan 23, 2002)

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.


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## Cinelli 82220 (Dec 2, 2010)

merckxman said:


> 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.


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## VKW (Jul 26, 2009)

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.


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## aclinjury (Sep 12, 2011)

VKW said:


> .....
> ...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..


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## VKW (Jul 26, 2009)

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.


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## aclinjury (Sep 12, 2011)

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.


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## jheeno (Jun 28, 2011)

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


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## looigi (Nov 24, 2010)

Kerry Irons said:


> 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.


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## orange_julius (Jan 24, 2003)

Cinelli 82220 said:


> 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


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## cxwrench (Nov 9, 2004)

Cinelli 82220 said:


> 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.
> 
> 
> 
> ...


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.


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## ewitz (Sep 11, 2002)

cxwrench said:


> ....... except for the BMC Impec.


???????


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## aclinjury (Sep 12, 2011)

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.


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## ukbloke (Sep 1, 2007)

My Tarmac claims to have a triple moncoque frame. If one monocoque is good, then three of them must be three times as good!


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## nhluhr (Sep 9, 2010)

Monocoque - Wikipedia, the free encyclopedia

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


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## JoelS (Aug 25, 2008)

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.


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## kathy20052012 (Jan 9, 2013)

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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</tbody>Vietnam travel-Mekong delta tour from hcmc-Halong bay cruise


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## cxwrench (Nov 9, 2004)

kathy20052012 said:


> 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?


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## wim (Feb 28, 2005)

kathy20052012 said:


> 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.


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## ewitz (Sep 11, 2002)

JoelS said:


> 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?


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## orange_julius (Jan 24, 2003)

ewitz said:


> 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.


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## aclinjury (Sep 12, 2011)

orange_julius said:


> 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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## aclinjury (Sep 12, 2011)

wim said:


> 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.



You're right about advertising bunk in the bicycle industry. Sure the improvement is there, sure the "technology" is there, but ultimately they are a minuscule contribution to the overall performance of its rider. But leave it to the bicycle marketeers to make these improvements seem like Nobel prize stuff.

I every time I read an ad of a high end racing bicycle, goes something like
- tapered head tube for stability
- oversized tubes for rigidity and lightweigt
- oversized bottom bracket for ultimate flex free power transfer
- shock absorbent rear triangle design for all day comfort

... and i'm thinking to myself... maybe Eddy Merckx and his contemporaries were racing on noodles back in the days... and surely Eddy The Animal must be producing girly wattage.. because surely today's Joe Weekend Warrior would easily break those flexy noodly steel frames with girly 1" steerer tubes that Eddy was riding on.


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## Cinelli 82220 (Dec 2, 2010)

aclinjury said:


> 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?


The tubes are woven onto a mandrel. Any modulus of fiber can be put anywhere in the tube, since instead of using pieces of fabric they are designing strand by strand. Theoretically the labor cost should be lower, since cutting pieces of fabric and laying them in a mold can be very time consuming. 
The weaving may someday allow for identical looking frames to have different levels of stiffness or weight, by changing the mix of fibers. A steel builder can use an SP downtube in an SL frame to stiffen it. The Impec system may allow this kind of customised ride tuning.
Molding the lug around the tubes should make them more homogenous/solid. Brushing glue onto a tube and sliding it into a lug may allow voids or bubbles. That shouldn't happen when molding.
From a manufacturing point, the biggest advantage would be consistency of product and reduced labor cost.

Just an example, I visited a small factory that made knitwear. They had a machine that made socks with logos (Nike, Adidas, sports teams etc) and pictures ( Disney characters). They machine was huge, with large spools of thread hanging from the ceiling. An operator picked a design from a computer screen and this thing started weaving socks with the pattern, and it took about 30 seconds to make a sock. It made 24 socks at once. 
After finishing one batch, the operator picked a different pattern, no physical contact with the machine was necessary. Just a selection from the menu. 
With this system one person was able to make thousands of socks in a shift, of several different designs.
They had a similar machine but bigger for making knit sweaters.
If BMC could get something like that up and running it would be awesome. Custom tuned carbon frames for your weight, size and riding style. Carbon fiber bicycle manufacturing is still in its very early stages. It's going to get far more sophisticated in a few years.


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## orange_julius (Jan 24, 2003)

Cinelli 82220 said:


> The tubes are woven onto a mandrel. Any modulus of fiber can be put anywhere in the tube, since instead of using pieces of fabric they are designing strand by strand. Theoretically the labor cost should be lower, since cutting pieces of fabric and laying them in a mold can be very time consuming.
> The weaving may someday allow for identical looking frames to have different levels of stiffness or weight, by changing the mix of fibers. A steel builder can use an SP downtube in an SL frame to stiffen it. The Impec system may allow this kind of customised ride tuning.
> Molding the lug around the tubes should make them more homogenous/solid. Brushing glue onto a tube and sliding it into a lug may allow voids or bubbles. That shouldn't happen when molding.
> From a manufacturing point, the biggest advantage would be consistency of product and reduced labor cost.


Thanks for the explanation. Ignoring costs, does the Impec/BMC method yield a better product or degree of customization compared to tube-to-tube with hand-cutting and hand-laying of carbon sheets/kevlar/glue/etc.? Or, is the latter limited by the resolution of fabric, instead of strands of fiber/kevlar?


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## cxwrench (Nov 9, 2004)

orange_julius said:


> Thanks for the explanation. Ignoring costs, does the Impec/BMC method yield a better product or degree of customization compared to tube-to-tube with hand-cutting and hand-laying of carbon sheets/kevlar/glue/etc.? Or, is the latter limited by the resolution of fabric, instead of strands of fiber/kevlar?


not sure about 'better' but i'll tell you one thing it isn't...lighter. the one i built was a 53 w/ the taller head tube and it was about 1350g. the fork was pretty hefty as well. the lugs are built in halves and bonded to the frame tubes in the mold after the tubes are woven around the mandrels to get the proper mix/pattern of fibres and the shape of the tubes.


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## Cinelli 82220 (Dec 2, 2010)

orange_julius said:


> Thanks for the explanation. Ignoring costs, does the Impec/BMC method yield a better product or degree of customization compared to tube-to-tube with hand-cutting and hand-laying of carbon sheets/kevlar/glue/etc.? Or, is the latter limited by the resolution of fabric, instead of strands of fiber/kevlar?


There is great potential for customisation...in a few years.
Tuning a carbon structure by varying the individual threads is far more effective and efficient than changing swatches of fabric. Currently, a builder will have to fetch a roll of fabric, cut out the piece they want, then roll up the fabric and put it back in storage. If the fiber modulus could be selected right in the weaving stage it would save lots of time.
Hand cutting always requires a margin of error. Every piece has to be bigger than necessary in case the cutter snips off a bit too much. That is why more expensive frames (McLaren eg) cost more. The cost goes way up because the person cutting goes much slower and more carefully, and each swatch is more carefully positioned in the mold. Most frames could easily be 10% lighter if these steps were taken, but the labor cost could double.
In manufacturing, a huge amount of time is wasted when people have to go to storage areas and get an odd item, or stop regular production to custom make one little piece. That is why a loom like BMC's has so much potential, not only could it offer tuning, it can make the whole process more efficient.


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## aclinjury (Sep 12, 2011)

cxwrench said:


> not sure about 'better' but i'll tell you one thing it isn't...lighter. the one i built was a 53 w/ the taller head tube and it was about 1350g. the fork was pretty hefty as well. the lugs are built in halves and bonded to the frame tubes in the mold after the tubes are woven around the mandrels to get the proper mix/pattern of fibres and the shape of the tubes.


1350g for a 53cm frame???


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## Cinelli 82220 (Dec 2, 2010)

aclinjury said:


> 1350g for a 53cm frame???


 That's not good.


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## JoelS (Aug 25, 2008)

The Impec I saw at a local shop also has a VERY slack geometry. If you like a bike that handles more like a ferrari, then it is not the bike for you.


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## deviousalex (Aug 18, 2010)

I can't find the videos right now, but they used to have videos that showed most of the Impec fab. The tubes are carbon weaves done 100% by machines. Look or Time doesn't do this, although they all 3 have carbon lugs. Supposedly each Impec tube is 100% identical.


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## BikesOfALesserGod (Jul 22, 2012)

Most men are monocoque


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## aengbretson (Sep 17, 2009)

Okay I haven't seen anybody say it (but then again I did skim through some parts).

The term "monocoque" is used to differentiate between frames that are molded in one, two, or three large pieces, from tube-to-tube style frames (either lugged or wrapped). It is rather difficult to mold the frame as one piece and as such we usually see the front triangle (head tube, top tube, and down tube) molded together, and then the rear triangle (BB, seat tube, and seat/chain stays) is glued to it. By minimizing any unnecessary wrappings or gluing the bike is a more solid piece. However, you are stuck with "off the shelf" sizing since moulds are obscenely expensive. Tube-to-tube bikes (i.e. Cannondale's super six) allow for custom geometries - see Peter Sagan's bike.


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## Jaguargod (Aug 29, 2021)

aclinjury said:


> 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?
> 
> ...


The KIRK Precision road bike and the KIRK Revolution MTB we’re both genuine monocoque frames. Both frames made from a single magnesium alloy moulding. Check them out google ‘Kirk bicycles’


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## cxwrench (Nov 9, 2004)

Jaguargod said:


> The KIRK Precision road bike and the KIRK Revolution MTB we’re *were* both genuine monocoque frames. Both frames made from a single magnesium alloy moulding. Check them out google ‘Kirk bicycles’


ftfy...And thank god you showed up to clarify this whole situation...8 and half years after the fact. Fantastic first post.


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## pmf (Feb 23, 2004)

And you're still as nice and good looking as you were 8 years ago. Fantastic English correction.


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