Late in 2018, after years of seeing parts generatively designed that were obviously frail and impossible to manufacture, were downright ugly, or offered no improvement over human designs, we issued a challenge to the engineering software vendors: Build a Better Bicycle Frame. Here was a chance to show how algorithms could think more creatively than the human brain. After all, that is how generative design was being sold. A myriad of possible designs would be churned out in short order, solutions that stuck-in-your-way engineers would never have thought to try. Maybe they were right. We did only weld tubes together to make a bike frame because we had tubes and we knew how to weld. It was not too creative. Yeah, we might be stuck in our ways.
So, it was with great excitement that we saw a company had decided to design a road bike frame using generative design. Decathlon, a sporting goods franchise that originated in France, the country that hosts the Tour de France, was going to accept our challenge. Now this was getting interesting.
We should be clear that our challenge was not officially sent to any generative design vendor—only published on engineering.com. Autodesk, whose generative design technology was used by Decathlon, did not formally accept the challenge, nor did the company even formally acknowledge it had read the article. In fact, no generative design vendors publicly admitted to being aware of the existence of the challenge, although there have been several off-the-record conversations accepting its premises. However, as a challenge has been issued and a response, official or otherwise, seems to have been offered, let us review Decathlon’s generative design bike.
Bike Design Review
Bike reviews are commonly conducted with a ride. As the Decathlon bike is only a “vision,” and we could not ask for the product to review it, we will judge the concept by what we know about it.
We reached out to Charles Cambianica, designer of the concept bike, quoted in Autodesk’s November 2020 post about the generative design, who confirmed that the bike frame still exists only as an artist’s rendering, although the fork has undergone detailed design. The design of the fork, using generative design, took three months, but Cambianica was doing other projects simultaneously. The bike frame will never be in mass production, and if it is ever produced, it will only be made to fill custom orders. There is no mention of generative design on Decathlon’s website and there are no pictures of the generative designed frame. Decathlon’s goal was to try to understand how generative design could be used for aesthetics primarily, and secondarily to explore performance gains. Most of Cambianica’s work is building prototypes of real-world designs, he says with a smiling emoji. As the bike is more or less a research project, we have no idea what a custom generatively designed bike would cost.
Meanwhile, let’s plow ahead. We find bike reviews of bikes that have actually been ridden practically useless anyway, with their authors waxing poetic about ride quality and claims of one material offering a more “comfortable” ride over another. Responsiveness, agility and flex is assessed subjectively without a single test measurement save a bathroom scale to record a bike’s weight.
The Decathlon bike is a road bike designed for time trials, a type of bike that is common in the cycling leg of a triathlon, occurring between the swimming and running events. The time trial favors a rider with a highly angled body to help reduce wind resistance. The rider’s hands and forearms are kept together to reduce wind resistance even further. It is an uncomfortable position. Also, such a design limits the use of the time trial bike. Hands together along the bike’s centerline cannot resist the torque from forces during hill climbs and sprints, so time trial bikes end up being used only for flat, straight courses.
As expected, the Decathlon generative design frame does away with tubes as a remnant of the past and starts anew, building the bike frame one tendril at a time, as bone-growth algorithms are prone to do, seemingly confined to an overall volume that maps to a conventional diamond frame.
The generative design process applied to the bike frame may require a suspension of belief. The belief that there is anything better than a round shape for resisting torsion (it’s important to reduce flex during pedaling load) and the belief that hollow shapes save weight. We marvel at nature, with the egg and its thin shell that we can’t crush in our palms no matter how hard we try. We have taken those beliefs to make pressure vessels, tanker trucks, airplane fuselages and submersibles capable of reaching the bottom of the deepest ocean gorges.
But what do we know? Do we need to resist high torsional loads on a time trial bike? The tendrils may be sufficient.
While maximum torsional loads may not be developed on a time trial bike, bike manufacturers consider streamlining to be of primary importance. A bare generatively designed frame may be an aerodynamic mess with streamlines unlikely to develop from its twisted geometry. It might have an overall increased projected area and have more surface and more surface drag. This is probably what led Decathlon to enclose the generative design with a clear, smooth covering over the fork and the front of the frame, as shown above.
But in its blog post about the bike, Autodesk mentions how using aluminum 3D-printed parts are more environmentally conscious than hydrocarbon-based plastic, the material used in carbon fiber bike frames, ignoring the clear plastic frame cover on the illustration above.
This is not the first time someone has tried to use generative design by Autodesk to make a bike frame. In a class at Autodesk University 2017, Autodesk’s Kenny Cornett and Michal Musiol teamed up to show generative design at work with an instructional demo titled “Design Space Exploration with Autodesk Generative Design.” What starts out as a serious look at the forces felt by the bike frames ends up as some of the most ludicrous bike frame designs we have ever seen as a result of generative design. The spindly structures produced were converged solutions to specific load cases (sprint, braking, etc.). An attempt to make a frame that could handle combined loads ended up as a most unappealing lumpy solid shape that gives a hint of “evolving” into a diamond frame. But perhaps we are, once again, favoring shapes we are familiar with.
Keep Trying
Just as concept cars at auto trade shows are measures of public reaction or just teases, Decathlon’s generative design bike may just tease us with what could be—a useful application of generative design in the offing, more substantial than the parade of generative designed brackets and not quite as ridiculous as a generative designed bridge.
However, held up against the diamond tubular frame as well as the suspension bridge, generative design continues to try hard but fails to improve on the simplicity and elegance of tried-and-true designs.
How Much Will It Cost?
Again, this is a concept only. The bike is shown as part of the Decathlon Van Rysel product line. We found the highest “real-world” Van Rysel with a conventional carbon fiber frame and Shimano 105 components for $2,499. This time trial bike, if it is ever produced, with the Dura Ace components shown, and custom made, will cost many times that amount.