Talking about monocoque

The term monocoque never goes out of style. It has even been called into question by Elon Musk during Tesla's Cybertruck presentation and is now widely used in many industries. The term monocoque comes from the French, literally "single shell" and was originally introduced in the field of boats [1-3], then transferred to the first airplanes to finally land in the automotive world thanks to André Gustave Citroën [4,5]. In general, in any closed vehicle, a monocoque is a structural shell capable of responding to external loads through stresses that are generated on the external skin without the need for a chassis for this function. The more the shell is closed and made up of a single part (mono), the more effective it will be in its structural function, just as it happens for an egg shell (coque), so fragile as to shatter between the fingers once broken, but so resistant as to require a decisive blow to break it as long as it is intact. Over time, the term monocoque was then "watered down" and revisited in a thousand keys of interpretation, sometimes called out in vain, generating not a little confusion and lending itself to some marketing tricks, as in the case of cycling.

Declined in the world of carbon fiber cycling frames, the term monocoque inevitably loses its link with the word “body”, since the racing bicycle is certainly not a closed vehicle. If you think about it, the same expression “monocoque frame” would be an oxymoron if it referred to a “shell that does not require an internal frame”: how could a frame exist that does not need a frame? Eventually, remaining in the pedal galaxy, the original meaning of monocoque could apply to some constructive solutions for fairing recumbent bicycles, the so-called streamliners, which having an external shell with aerodynamic function, can be designed in such a way as to give this also structural tasks. The same universe as human-powered vehicles in which the bicycle also falls, the same galaxy of pedals and leg muscles, but another solar system compared to the traditional bike.

Returning to this planet, in the cycling industry the term monocoque takes on a very different connotation and indicates a manufacturing process that takes place “in one piece” through the use of a mold. Also here, as well explained in [6-8], there are at least a couple of nuances: integral monocoque “rear frame included” (rare) or referring to the main triangle only (more common), but in both cases the common denominator is the “one-piece” construction process by means of a mold, which excludes the use of pre-formed tubes which are joined in a second process phase by gluing, wrapping or co-molding.

What changes? More than you imagine. The design and the shape first, that are severely limited when using preformed tubes to be cut. And then the layering of prepregs done on a single mold offers optimization chances that fade out when finished pipes must be joined. The downside is that, at least to date, the use of a mold prevents the construction of tailored frames that are truly monocoque: for custom size, preformed tubes are still needed to be cutted and joined in subsequent steps. The joining process can be more or less evolved from a technological point of view, it can take place by involving molds again and result in a pleasant and structurally effective product to the point of looking like a monocoque to the inexperienced eye, but between “looking like” and “being” there’s still a clear line of demarcation.

Why is Gregario talking to you about monocoque? We will tell you about it in one of the next episodes, stay tuned and when you come across someone who wants to sell you a monocoque frame, sharpen your eyes… if you really don’t know how to find and understand his patents, look at the construction details and photos of the process it divulges: in short, keep an eye on preformed pipes and co-molding, which certainly offer their advantages and are not technologies to snub at all, but it is correct to expect that they are not passed off as monocoque.

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Latest from the Blog

Blog | 01 November 2024

Sizing & Fitting: the synergy that makes your ride perfect

Have you ever wondered why some people seem born on their bike, while others struggle to find a comfortable and efficient position?

The answer, largely, lies in two fundamental concepts: sizing and fitting.

Blog | 21 October 2024

Digital Sizing by Gregario

Defining the optimal dimensions of a frame it’s always a fascinating challenge. Even more so is calculating the optimal measurements of the entire bicycle, that is, that set of geometries that lead to a total harmony of ergonomics and handling, from the saddle point to the hoods (hand points) and to the pedal (shoe points).

Traditionally, designing custom bicycles requires the physical presence of the cyclist at the manufacturer’s headquarters or the retailer, which can be limiting and can make the tailor-made accessible to a very small subgroup of amateurs, not only for economic reasons but also for logistics and time.
The world of bike fitting has developed over the years a series of “recipes”, empirical methods refined and handed down over the years, evolved as new equipment has entered the bike fitter’s study, but often oriented towards the ultimate goal of adapting the athlete to an existing frame. Usually, replacements and/or micro-adjustments of the saddle, stem and handlebars are proposed to improve the posture, rarely achieving perfection only when the starting point already falls within the ideal values… it is certainly not possible to compensate starting from a frame with inadequate measurements.

Here’s why sizing of the frame is important, whether it’s identifying the most suitable standard size or, better yet, starting from a blank sheet of paper and setting up the project for a new tailor-made special.

But what is Gregario’s proposal on this subject? Well, it all depends on your starting point…

Case A) Do you already have clear ideas?

Chances are you already have a trusted bike fitter or a dealer equipped and capable of defining your ideal contact points… or let’s say you have an old bike that fits you like a glove and you want to replicate that exact positioning on a modern monocoque but does not match with standard sizes… or let’s finally suppose that you already have your ideal measurements in your head because your great-great-grandmother told them to you in a dream. Well in all these cases no sizing method is necessary, you’ll just have to communicate us these essential data clearly, i.e. those reported in the following table in reference to the diagrams below:

Xs	Horizontal distance from BB center to saddle contact point (approximately where the saddle is wide 70 mm)
Zs	Vertical distance from BB center to saddle contact point (see above)
Xc	Horizontal distance from BB center to hand contact point (hoods, approximately at the point of support in the palm at the base of the thumb)
Zc	Vertical distance from BB center to hand contact point (see above)
W	Handlebar width (measured at the center of the controls)

If necessary, also provide information on the driving style you prefer, so we will take this into account during the design phase to set the length of the stem. Our cockpit also provides the possibility of adjustment of the stem angle, but the basic reference is with horizontal stem (parallel to the ground) and any variations in the angle are intended for micro-adjustments (e.g. seasonal) as well as the saddle adjustments: up to ± 3 cm in height and the classic forward/backward depending on the chosen saddle model. These are the reference schemes for the measures to be provided if you already have all the tools to define them independently.

Blog | 29 March 2024

Handmade

At Gregario, we have always cultivated esteem and respect for the artisanal frame-building tradition of our beautiful country, which is dedicated to a niche of timeless “classic” products, primarily made from steel, but also incorporating wrapped carbon and other techniques specific to small workshops.

So long live frame builders and anyone dedicated to preservation and pass on a noble and fascinating ars technica !

That said, we recently came across some social media posts from several respected bicycle craftspeople who, while rightly praising the (undoubted) qualities of their frames, contrast their “handmade” products with “moulded” monocoque carbon frames. On the face of it, this seems like a legitimate claim, but this narrative leads to significant misinformation about HOW such “moulded” frames are actually produced… namely, with manual work that is decidedly more demanding and onerous than any technique for joining eight tubes.

Yes, because we are not talking about printing cookies, but rather about carefully arranging over 200 fabric shapes (pre-impregnated carbon) inside a mould. These pieces range from 40 cm strips to tiny stamps, all positioned by hand according to a precise plan (the ply-book) with meticulous overlaps, folds to manage and fibre orientations to respect. And this is only half the work, because then, depending on the resin curing technology used, there are a further series of steps involved, always rigorously by hand.

In the case of autoclaves (the most common technique in Europe), it is necessary to carefully position the internal bags, close the two half-moulds without pinching anything, arrange a series of auxiliary materials, close the external bag, apply the putty to connect the internal bags with the external and so on until the whole thing is cured under high pressure and temperature. Furthermore, once the curing is finished, it’s back to manual work for mould opening, part extraction, and finishing. All this with a series of possible variations we won’t go into now.

In short, there is nothing more “handmade” than a carbon monocoque frame.

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