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Smoothness as a performance metric: Berd’s case for why vibration is part of rolling resistance
Many brands within the bike industry often speak about higher-performing products being stiffer, lighter, more aero, and faster-rolling. And yet when it comes to off-road disciplines, it’s rare for brands to discuss smoothness as a performance metric. It’s an area many have dabbled in over the years, but it’s tough to market a product on.
Berd, makers of rope-like spokes, recently published a white paper detailing why they believe their new gravel race wheels are the fastest for the off-road discipline. A big part of that claim relates to vibration damping and impact reduction, metrics that historically haven’t been included in the performance modelling used today to calculate a road cyclists’ speed.
In its white paper, Berd proposes that vibration damping and impact reduction should be included as a component of rolling resistance. As someone who has long shouted as much for off-road – smoother is faster – I thought that was all quite interesting. So I sat down with Berd co-founder and CEO, Charlie Spanjers, to hear more. This discussion was recorded as a podcast, but we’ve also included the transcription for those who prefer the written word.
_****Note:****___This transcript has been edited for clarity and brevity.__
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**Dave Rome** : **Let's let's start from the beginning. What’s your background? And what’s a Berd?**
Charlie Spanjers: Yeah, absolutely. So I'm a cyclist. I'm a chemical engineer, and I founded Berd about 10 years ago with two good friends of mine, Brad Guertin and Kyle Olson, and we were coming off our graduate degrees and trying to figure out what's next.
We were wanting to start a company, and we had come up with two distinct ideas. So we had the bicycle spoke idea that we were going to go back and create prototypes in my apartment and see if we could make it work, and then the other idea was a peanut-butter-filled banana. So that when you open it up on the inside, you have this delicious food for cyclists. You know, it would be this great idea. We made prototypes for both the banana and our super lightweight bicycle spoke made out of Dyneema, and we decided to pursue the bicycle spoke, obviously.
The name Berd stands for bike nerd. We're bike nerds, and our original idea was to make a bicycle spoke out of Dyneema that would be lighter than steel spokes on the market, and yet stronger at the same time. And at the time, that was the biggest benefit we thought there would be. We thought we would make the world's lightest bicycle spokes, and you know, with lighter-weight spokes, you can ride faster, further, climb hills faster, and that would sort of be the biggest benefit and the end to it.
Diving deep: Reviewing Berd polymer vs steel-bladed spokesEver seen those white spokes on Pidcock’s or Ferrand-Prévot Olympic-winning bikes and wondered what they’re all about? I wanted to answer the same question for myself.Escape CollectiveDave Rome
What we realized over the years is that it's not just the light weight of the spokes, but it's that this material, which is ultra high molecular weight polyethylene – it's in many ways similar to polyethylene that you have a plastic bag made out of, but it's made in a very special way that makes it so strong. The one sort of accidental benefit of this polyethylene is that it's viscoelastic, and so it gives a super smooth vibration damping feeling that has taken us a long time to quantify.
We've gained so much success in mountain biking, I think, because of this very special thing about the material. One story I like to tell is that in the beginning of 2024 – the year of the Paris Olympics – Tom Pidcock and Pauline Ferrand-Prévot rode our spokes for the first time. Rune Kristensen, the mechanic at Ineos _[ Kristensen has since moved on to another team – ed.]_ , had given the two riders our spokes to try, and they rode them for the first time, and they said these are so smooth that they were never going to ride anything ever again for mountain biking.
They went on to both win Olympic gold. Since then we've had 50 World Cup podiums with six different teams on the World Cup cross-country mountain bike circuit riding our spokes, a total of four Olympic medals, and five World Championship medals. We've gained a lot of success in the last couple of years because of the light weight and the smoothness, in particular, that you get from our bicycle spokes.
**DR:** **That smoothness is the point of this conversation, and certainly a large part of the white paper you recently published. That white paper published alongside a new product release. What was that product release?**
CS: That was our Sparrow 50 Gold gravel wheels.
We had first launched a Hawk 30 Gold mountain bike wheel in February, and those are extremely lightweight mountain bike wheels, pushing the limits of what's out there from any other major bicycle wheel manufacturer. We've had a lot of success with those wheels, and so we wanted to create a gravel wheel that had a combination of aero, light weight, and vibration damping that would then make it the fastest. Not one individual attribute, you know, not necessarily the most aerodynamic, but considering everything a gravel wheel needs to do, we wanted to show through science and modeling that it is one of the fastest wheels out there.
The new Sparrow 50 Gold.
**DR:** **That modeling is going to make up a pretty decent sized chunk of this conversation, and is a big part of what that white paper was. Let's start with the basics. Can you explain the pre-existing version of the modelling that's commonly used, what it does account for, and what you're trying to add into it?**
CS: Yeah, modeling a bicycle wheel and the physics behind the speed of an entire bicycle is not new, of course. The paper I looked at for some background was from 1998, but that wasn't the first of modeling a bicycle, and of course it's not the last either. But when you look at a cyclist's power, there's six components that a rider’s power is consumed by. The big one is aerodynamics, and I think most people understand that aerodynamics is so important in bike riding. The key term you hear a lot is the CdA term, which is the drag coefficient multiplied by the area. It’s a term that you can use to compare across different components or rider positions. Aerodynamic scales with velocity to the cubic power. So that means that if you double your speed, you have eight times as much air resistance, assuming all other things being equal.
The next term relates to rolling resistance. I think a lot of cyclists have thought about that at some point – maybe you've gone to bicyclerollingresistance.com to compare tires to see which ones have the lowest rolling resistance on the road. More recently, people are looking at rolling resistance for off-road as well, and so we'll talk a little bit more about that here.
Then you've got gravity which dominates when you're going up a steep hill.
Aerodynamics dominates at high speeds on flat ground. Rolling resistance can dominate on really rough surfaces, rough gravel, rough signal track, rough grass.
Then you've got the inertia term. So if you're going to accelerate, that consumes your power. Lastly, you've got a couple of smaller components included in the model which are the drivetrain efficiency, which is fairly small and not necessarily a factor of many other components, and then wheel bearings.
So those six terms, if you look at that equation – you've got power equals the sum of all of these different things, and then if you want to figure out how to go faster at a constant power, you can change any of these components. If you have a different coefficient of rolling resistance (CRR), or you have a lighter bike, or if you have something that's more aerodynamic, you can then use that full equation at a given power to see how much faster you'd go.
Or alternatively: say, I did the course this fast. If I had done X and Y differently, or used this different component, I would have saved this many watts, for example. And so that's the power of modeling everything and having that equation – now you don't have to rely on one single number. Instead, you can answer how much does the weight affect me, and how does that balance against aerodynamics? It gives you the power to be able to look at the complete picture.
This sort of modeling has become more popular in the last couple of years. For example, Specialized mentioned the calculations they did for the new Crux, and then they published a white paper on the Tarmac as well. One thing that I wanted to do differently, though, with what we were doing with these wheels, was to actually publish all the equations and all of the data that went into it. And for a manufacturer, that was the part that I thought would be fairly unique, because most of the time, I see fragments of data rather than full equations.
**DR:** **I think a lot of brands are often accused of handpicking the data that sells the story. It's not always a full picture, and it sometimes presents more questions than answers. What stood out to me with your white paper is that it gets into areas that a lot of brands don't have data for, or tend to be a little bit fearful of trying to put numbers against.**
**The modeling you just spoke of is pretty robust on the road, like in a smooth surface race. It's been being used for years now. They can pretty accurately calculate the finish time on Alpe d'Huez, or something like that if they know a rider’s metrics. But off road, I feel like it's a different story. You've got more dynamic terrain. You've got these vibrational losses. You've got more going on, and I think that's something that you're starting to address, which is very interesting.**
**Let's talk about that. What metrics are you looking to add to that modeling that you just described?**
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