Study: aerodynamics is more important than the weight of the wheels?
Everyone has long been well aware of the fact that the lighter the wheels, the faster you are on acceleration, and in some situations on braking. The riders who were changing wheels on a lightweight, for sure, could feel the increase in acceleration. There are a lot of adherents of this theory, less often there is an opinion that the weight of the wheels ultimately has less influence than, for example, the aerodynamics of the same wheels.
I was one of the former myself, up to a certain point. We even wrote an article where we destroyed this myth. However, based on studies dating back to 2001, it can be argued that weight does not play the first role in accelerating and maintaining speed. When I first saw this information, I was somewhat confused… how is it, i felt it myself, i turned these pedals myself, i picked up speed faster!?
In conversations with my cycling friends, I did not find understanding, no one believed me, they are all as convinced as I once was-with light wheels you can accelerate faster. In fact, it turns out that in order to feel the difference in the weight of the wheels in acceleration, acceleration must be far beyond the physical capabilities of a person. On the other hand, information about road bikes for uphill pops up in my head, they are made as light as possible. Yes, they are being made. Yes, only because it is easier to drag 6 kg up the mountain than, for example, 10 kg.
in general, all this i say to the fact that in this article we make another attack on the stereotype ingrained in the minds of many cyclists about the incredible impact of the weight of the wheel on acceleration and the ride as a whole. true, we will talk about road equipment, although all this is also true for mtb. i have seen tests of guys who tried downhill in classic mtb-shny spacious clothes, and then in tight cross-country ones. Yes, tight-fitting clothing allowed you to win a few seconds of time on the descent, which surprised the tester, aerodynamics in all its glory.
So, let’s go back to the wheels and talk about them.
1. The slower, the more important the aerodynamics.
Well, up to a point. The name of the first item is unsettling. Although the graph states exactly that.
Let’s look at what is displayed on it at all. The graph shows the dependence of the aerodynamic drag of the wheels on the angle of attack of the wheel. The blue curve at the bottom shows the characteristics of the Argon18 TT racing bike, we don’t need it.
Let’s focus on the four upper curves, which characterize the aerodynamic drag of the Cervelo R5 bike on four different vilsets from the Swiss Side company. The blue curve belongs to Heidi wheels, red wheels Hadron 800+ with height of rim is 80 mm, orange Hadron 625 with a height of 62.5 mm and green with the same wheels, but with the height of the rim of 48.5 mm.
What is the angle of attack?
This is the angle at which the wheel meets the incoming flow of air (wind). If the wind is directed strictly in the center, then the angle of attack is zero, if the wind runs strictly to the left or right, then the angle of attack is 90 degrees. Basically, we’re talking about yawing, which combines the speed of the incoming stream, its direction, and your own speed.
The first point in the middle of the graph shows the aerodynamic drag of the wheels with zero angle of attack, it is approximately the same for all models. Differences appear when the yaw angle increases. it is also important to say that all rims (except one) are made not according to the classical scheme with straight outer walls, but according to the toroidal scheme. This means that the wheel profile is similar to a bagel. This solution is justified by the best aerodynamic characteristics in comparison with the classic one.
Then the magic begins. Up to an angle of 6 degrees, all wheels increase their resistance, but only Heidi wheels maintain this trend up to 12 degrees. Hadron wheels, on the contrary, begin to reduce their resistance from the mark of 6 degrees and begin to increase it from 12 degrees.
This is how the toroidal shape of the rim works, it is designed to reduce the lateral air resistance. The straight wall on Heidi copes with this task much worse, but rather does not cope at all, turning into a sail.
professional athletes drive at high speeds, where yaw angles do not exceed 10 degrees, which turns out in practice. The wheel is simply leveled by the flow of incoming air. But according to the graphs, we can see that the wheels start working much more efficiently at large yaw angles. And this is surprising, it turns out that the slower you go, the more important the aerodynamics of the wheel in the context of crosswind, although logic suggests quite another. It becomes even more interesting when you know that the aerodynamic drag increases in proportion to the square of the speed, that is, from the point of view of energy consumption and aerodynamics, it is more expedient to slow down.
2. the wrong tire levels the aerodynamics of the wheel.
A proper aerodynamic tire often contains some pattern to the left and right of the treadmill, which creates a certain surface roughness. it is necessary in order to create a turbulent layer that will hold the incoming flow at the rim surface.
In the tests we are talking about, the Continental GP 4000S tire took part, it just contains such a pattern. Although according to the researchers, the presence of a pattern and good aerodynamic performance in this particular case is only a coincidence. However, some manufacturers take into account the factor of creating a turbulent flow and reflect this in their “tread ” pattern. Yes, because many of these patterns seem necessary for better traction, however, this is a separate topic, which we also discussed.
These tires allow you to keep the air flow on the wheel at yaw angles of 18-20 degrees. On the contrary, tires with a completely smooth profile lose their aerodynamic effect at yaw angles of 8-10 degrees.
It turns out that choosing a cool and incredibly light tire for uphill with flat sidewalls loses a big advantage in aerodynamics.
3. Weight is a secondary problem almost all the time.
In fact, yes, almost every time we run into the problem of aerodynamics faster than the problem of weight.
Swiss Side conducted tests sending riders to a distance of 120 km and a rise of 1200 meters with an average power of 211 watts. In their deep belief, this is what the average rider looks like. Well, the target audience of the company is clear, it is not about beginners and amateurs.
The company’s wheels are made of carbon fiber, but the brake track is made of metal, which adds 100 grams to the design. It seems like a lot. But let’s imagine that the bike weighed 8 kg, and became 8.1 kg with the weight of the cyclist in 75 kg. Can these 100 grams really play a big role? Role-yes. not a big one.
Three seconds of savings. Three seconds of savings on a four-hour trip. Adding only 100 grams (1.25% of the total weight of the bike) does not play a special role. Even if we increase the weight by 400 grams, the time difference is only 17 seconds at 120 kilometers.
If we increase the aerodynamic drag by 1.25%, then the rider will arrive later by 22 seconds, increase to 5% and get 87 seconds. Just a minute and a half for 4 hours of travel is not much, yes, that’s right. But this is much more than if we increased the weight by the same 5%.
The numbers speak for themselves.
However, there is a tipping point when aerodynamics recedes and it is weight that comes to the fore. On a 20-kilometer incline with an average gradient of 4% or more, weight begins to play a greater influence, and aerodynamics becomes secondary.
That is, when choosing a bike for specific conditions, most often you will have to chase not for its low weight, but for its aerodynamics. Of course, a 10-kilogram bike will not be faster than a 6-kilogram bike, everything has a reasonable limit. But every time you want to lose a couple of extra grams, you should probably forget about it and take care of the aerodynamics of the bike.
Such things, gentlemen, the stereotype is bursting at the seams. The research is accurate and unbiased, as it is repeated in each individual manufacturer, that is, it is not some alternative point of view that requires verification. rather, the claim that light wheels are faster is an alternative point of view that should be treated with great caution.