Adopted by Aprilia on its 250cc at the beginning of the 2000s, the carbon swingarm was then popularized by Ducati from its GP9s before making its appearance at Honda at the 2017 Valencia post-GP test.
Used since by Marc Marquez and Dani Pedrosa during the first Grand Prix of this 2018 season, we are now waiting for Aprilia version, and the circle will (perhaps) be closed.
THEinterview of Conrad Cecchinelli created by Peter Mc Laren for the site Crash.net on the subject is particularly interesting since not only does the Italian serve as Director of Technology for Dorna, but he also worked for Ducati from 2006 to 2010, SO during the GP9 era. The man therefore knows his subject and reveals some anecdotes to us.
Excerpts…
Crash.net: Corrado, were you at Ducati at the start of the carbon fiber swingarm project?
Conrad Cecchinelli : " Yes. I was at Ducati when we started with the carbon fiber swingarm. It was not the first time that this had been done, because it was already on the 250cc Aprilia for example.
Carbon fiber is the appropriate material if you are using large, thin surfaces, but not small shapes. So for me this is the correct application for a swingarm, also because the swingarm is designed for rigidity.
This does not mean that it is designed to be as stiff as possible, but that it is designed for a defined stiffness.
Plus, you want 3D rigidity. For example, you want the swingarm to bend when the motorcycle leans, but not twist. With carbon fiber, you can play with the orientation of the fibers to have the three-dimensional stiffness you want.
Likewise, in general, for a given target stiffness, and given the necessary strength, a swingarm will likely be lighter if made from carbon fiber than aluminum.
But I can tell you that when I was at Ducati, the MSMA (Manufacturers Association) tried to stop carbon fiber swingarms because they were afraid it would be expensive. Which is true if you only consider the cost of a single part, but not for a season of swingarms.
We were the joke of the MSMA because we said it was a savings! But it's true because when you design an aluminum swingarm for a set stiffness, it can become so thin that it splits under normal use. And this is what is happening, even today! Carbon fiber is therefore not automatically more expensive.
However, it's definitely more difficult to make a carbon fiber swingarm and a single piece is more expensive than a single piece of aluminum, that's for sure.
Additionally, there are concerns about security. This is not because carbon fiber is less safe, but because the outcome of a collision in terms of possible swingarm damage is more difficult to study with carbon fiber. After a big accident, you have to send the swingarm back to the factory for x-rays and other complicated inspections. This is not something you can do at the track.
This is one more reason why carbon fiber is an expensive part, because you need to have more spare parts, so you can change the swingarm after a big crash to be safe.
So there are issues with using carbon fiber. But still, if you ask me, this is the right technology to make a swingarm. Because of the benefits I mentioned. »
Crash.net: Then why doesn't everyone in MotoGP use them?
Conrad Cecchinelli : “First of all, if you don't push the [thickness] limit of aluminum in your swingarm design, then you won't have the problem of insufficient stiffness with the stiffness of your target .
And in this case, the example I gave you of carbon fiber costing less over an entire season doesn't apply. Because if the aluminum is not designed to the extreme, it will not need to be replaced as often.
And then there are the other reasons why I told you: it's difficult to design, difficult to produce, suspect in the event of a big crash. For all these reasons, the conventional technology is aluminum and of course it gives more than acceptable results, since it is the most commonly used technology today.
But carbon fiber is even better for me, with drawbacks. »
Crash.net: So performance-wise, you can get more flexibility with carbon fiber because you don't have the problem of making the aluminum too thin?
Conrad Cecchinelli : “In designing a swingarm for racing, you are looking for something anisotropic, meaning that has different stiffness properties in each direction.
Carbon fiber helps you with this because you can put more or fewer layers of carbon fiber in certain areas and you can have different orientations of the fibers. Changing the orientation of the fibers modifies the stiffness.
The swingarm will probably also end up being lighter with carbon fiber, but it's worth remembering that carbon fiber has naturally different damping than aluminum. So if you have issues like chattering, or vibration in general, you might want to switch from one to the other [carbon fiber to aluminum or vice versa] just because the other arm oscillating will have a different weight and different damping.
This is another reason to choose one or the other. It's very complicated, but the small difference in weight and interior damping can affect chattering and vibration in general. »
Crash.net: A popular conception is that carbon fiber is too stiff for motorcycle racing…..
Conrad Cecchinelli : “That’s not true! Rigidity is simply a design goal.
In general, when designing mechanical parts, you may first look for a defined stiffness or a defined strength.
It doesn't always go together. If you are designing a hook to lift a large weight, your main design goal is strength, which generally brings with it the greatest possible rigidity.
But if you're designing a swingarm or a chassis, you're designing for a set stiffness. And, in reaching that stiffness goal, you may not have enough resistance. This can be the case with an aluminum swingarm.
For example, you may want it to be so flexible that you risk cracking. Or even if it's not that extreme, what happens is the sheet metal becomes so thin that welding is a problem. Things like that.
So, parts designed for a set stiffness are not necessarily strong enough to be made from aluminum. »
Crash.net: It's interesting, because people feel like when they go to carbon fiber, they want something stiffer….
Conrad Cecchinelli : " No ! They are looking for ideal rigidity, but with less weight and more strength. Or they are looking for better differentiation of stiffness in each direction. Because in general for a swingarm you want it to be able to act as a suspension in lean, but not in braking and not in twist.
If you're good with carbon fiber, you're more likely to succeed. »
Crash.net: Do you think it's just a coincidence that Honda and Aprilia are starting to use this technology on their MotoGP bikes this year?
Conrad Cecchinelli : “I don't know, it could just be something that is not clearly identified but is perhaps induced by the new tires.
It could be a generation of tire casings that suddenly makes carbon fiber better than aluminum, due to the material's damping behavior. But I'm only guessing.
Let's say you're an R&D department and you're designing your best possible carbon fiber swingarm and your best possible aluminum swingarm. You have a difference of half a kilo, so you try carbon fiber and it turns out it's better for chattering. It depends on the tire, but that wasn't your main target. »
Read the rest of the interview on the Crash.net website
