CFD analysis to support the bike designer

Computational fluid dynamics analysis (CFD) is a simulation technique applied also in the sporting goods industry. Roughly summarized, CFD consists in discretizing a volume of fluid in many cells (in the order of millions for a bicycle) and solving for each cell a series of equations until the convergence of the calculation. Skeptics will say that in most cases for the bike industry it’s just Colorful Fluid Dynamics for mere marketing purposes, but one should not confuse what is shown on “the surface” with what is actually studied and kept confidential in order not to give precious informations to the competitors.  

The growing availability of computational power at low cost and the maturity reached nowadays by simulation softwares allows for a depth of analysis that professional bike designers and product development teams cannot ignore. Especially in a highly competitive market where marginal gain is increasingly determining the difference between a success (sporting and/or commercial) and a mediocre result or, worse, a debacle.



Before CFD became an accessible tool, the traditional approach to evaluate the aerodynamics of a bicycle involved the use of the wind tunnel. This had a strong impact on costs and few possibilities to proceed with a wide comparative development. Unless you have an unlimited budget, the use of the wind tunnel alone places severe limitations on the possible design variants to be compared. However, the tunnel remains a fundamental reference for providing the experimental feedback necessary for the so-called “calibration” of numerical models. Given the variety of possible modeling approaches and parameters (type of mesh, type of analysis, turbulence and transition models for the boundary layer, etc.) it would be naive to blindly trust a numerical result without any experimental validation. Or, more frequently, without an experimental reference that allows to tune such parameters so that the model becomes reliable.

So where is the usefulness of CFD if it still requires experimental feedback?

Here’s the good news: given a fluid dynamics problem (i.e. a bicycle at a certain range of speed and wind angles), after tuning a model over a reference experimental setup, it is not that modifying the frame or a component will radically alter the physics of the problem itself. Especially if the changes are within UCI rules. Once the model parameters have been correctly tuned and the underlying physics has been properly chosen, the model is sufficiently robust and reliable even for subsequent design changes. In addition, modern CFD analysis softwares have now evolved in the direction of providing an integrated platform for optimization: this allows to explore a large design space in a time frame that was unthinkable even just 10 years ago.

Gregario offers B2B consultancy activities to the cycling industry including his knowledge and experience in fluid dynamics analysis. Working with Siemens StarCCM+ for CFD, Gregario is able to support the entire product design cycle with detailed analysis and accurate reporting of the aerodynamics development of frames and components. All with traditional 100% armored confidentiality that distinguishes a faithful Gregario.

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Blog | 29 March 2024


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.

Blog | 11 August 2023

Cycling meditating

Every successful ride is first and foremost a meditation activity.

Sooner or later along the way, we find ourselves entering a sort of trance: the lungs ventilate, the heart pumps, the muscle memory becomes automatic pilot: intensity, timing, coordination, reflexes. At this point, the brain has “only” to keep an eye on potholes and other road users (and that’s no small thing), but, considering the available computing power, it finds itself unemployed on average. Daily problems are suddenly summoned to a quick and decisive mental meeting: what can be solved is solved, what is not important is reduced, a sudden “lateral” gaze opens up on what seemed insoluble. The shower upon return consolidates the thoughts, fixes the fundamental ideas and we are ready to face new personal and professional challenges.

However, all this happens only on one condition: the absence of pain. Fatigue isn’t a problem, that’s part of the game, it’s wanted and desired by the cyclist, but pain is a whole other story, pain ruins everything. A knee that becomes inflamed, an insistent discomfort in the neck or an unexpected burning in the groin can compromise all the meditative pleasure. The brain can’t focus on anything else: “Maybe if I go back a little on the saddle… no, now I’ll try standing up… nothing to do, I’ll go back to gripping high… nothing, maybe a sprint will help to unlock, nope… what do I do? I know I have to go back.” Missed goals and consequent disappointment.

Then, maybe, you wait a few days, even a week and try again. And what a frustration when that pain makes itself felt again, perhaps even after a few kms in which it has left us harboring the illusion of a successful ride. Even in the hypothesis of lowering the pace and concluding the following rides without problems, the mental state is compromised: one spends the time listening to the nerves, registering every slightest signal, in fear of recognizing the beginning of that pain again.

In the worst case, you enter a loop of medical visits, bike-fitting sessions, saddle/handlebar/stem/riser/cleat/adjustment changes/etc. And in all of this we stop at a certain point to think: where is that pleasure of getting on our most faithful bike, taking the road and quickly entering that meditation bubble?

Anyone who has known this path knows that a custom frame represents the most effective and long-lasting solution. A custom frame is designed to adapt to the physical and morphological characteristics of the cyclist, ensuring optimal posture, balanced weight distribution and less pressure on the joints. Thanks to this customization, the risk of experiencing pain and injuries is drastically reduced, allowing you to fully enjoy every pedal stroke and to keep your mind focused on the essence of the journey. Investing in a custom frame is investing in your physical and mental well-being, rediscovering that meditation in motion that makes cycling one of the most rewarding and liberating experiences. Only in this way will the cyclist be able to rediscover the true meaning of that meditation bubble on two wheels, where the body, the mind and the road merge in perfect harmony.

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