In today’s cycling, there is a continuous search for marginal gains. Bicycle manufacturers, cyclists and teams try to find new ways to take their performance to the next level. Team DSM is one of the most performance (and science) driven teams in the UCI World Tour. We had the chance to talk with Team DSM’s Aerodynamics Expert Harm Ubbens.
Harm obtained his MSc in Aerospace Engineering at the Technical University of Delft. During his Master’s course his interest started to shift from airplane to sports aerodynamics. As a result, he did his thesis on bobsleigh aerodynamics. He also helped design the wind tunnel at BikeValley in Belgium during his internship and later on worked there as aerodynamicist and wind tunnel operator, before joining Team DSM as their Aerodynamics Expert.
A history of cycling aerodynamics
In the past, there have been a number of pioneers in cycling aerodynamics. For example, Greg LeMond in the finishing time trial of the Tour de France of 1989. He was the first cyclist to use an aerobar extension on his steer as well as wearing a profiled time trial helmet where other riders wore just a cap, or nothing at all. This allowed LeMond to ride in a more streamlined position than other riders and gave him the required edge to win the Tour de France over Laurent Fignon with only an 8 second time difference on over 87 hours of cycling.
Graeme Obree was another pioneer. Working towards his world hour record attempt of 1993, he built a bike using parts of his washing machine. He combined this with extremely compact or stretched positions on his bike, breaking the world hour record twice.
The importance of aerodynamics in cycling
In general, cycling can be seen as overcoming resistance. On the flats, about 90% of the total resistance a cyclist feels, is his aerodynamic drag. If you can minimize this, the cyclist can go a lot faster with the same power output, allowing him to gain time upon his competitors. When climbing with very steep gradients, the relative importance of aerodynamics decreases as the importance of gravity increases. Luckily, there are many ways to improve aerodynamics, through special clothing or custom components for example. Changing gravity, by contrast, is quite difficult. So aerodynamics is definitely one of the most important factors that can be influenced to increase performance. It is, however, important to always optimize it in combination with other aspects like ergonomics – the most aerodynamic position usually leads to a reduced power output and as such, does not make the cyclist faster.
Aerodynamic cycling positions
In general, every pro rider is into aero aerodynamics, but you could divide the peloton in two groups. The first group are those specialized in climbing. The second group are the more powerful riders. If you belong to the second group, you cannot ignore the significance of aerodynamics. There are some examples of riders willing to do everything they can to go faster. World hour record holder Victor Campenaerts is a good example of a rider who is really into aerodynamics. He is prepared to do everything to improve his aerodynamics, including getting into almost incredible positions.
Bike versus rider
For sure, the bike is an important part of a cyclist’s aerodynamics, but not as important as the position of the cyclist himself. As an amateur, you would get a lot more value for money when you optimise your position through a bike fitting compared to buying an aero bike.
Aerodynamic innovation within the UCI rules
Today, it’s still possible to improve the aerodynamics through continuous innovation in terms of production methods. The biggest evolution over the last five years is probably the integration of braking & shifting cables. These cables are round and tend to feature a lot of flow separation, reducing the flow quality along the body and frame. Integrating these cables provides a significant reduction in aerodynamic drag. Apart from that, it has become quite difficult to improve the aerodynamics of a bike within the UCI rules. Typically, an aerodynamic bike is heavier due to the special shapes and this has a negative effect when a cyclist needs to climb. That is why bike manufacturers are now aiming to make the most aerodynamic bikes as light as possible. Examples of bikes that are both aerodynamic and lightweight are the Scott Addict RC and the S-Works Tarmac SL7.
Future innovations in cycling aerodynamics
When manufacturers switched from steel frames to aluminium ones, a lot of research was performed on the shape of the tubes. The switch from aluminium to carbon frames again triggered a boost in R&D on tube shapes. Then followed the integration of cables and focus on weight. The future will probably involve a more holistic approach: to optimize the combination of rider & bike, including his position and equipment. This is in contrast to the current way of trying to optimize a bike, a pair of wheels, a helmet, etc individually without too much consideration of the interaction with the cyclist, who will experience unpleasant ergonomics when trying to adapt his position to the equipment, rather than the other way around.
Components of aerodynamic drag
The aerodynamic drag on a cyclist can be split into skin friction drag and pressure drag (learn more about aerodynamic drag). Skin friction is the result of the air sliding across the surface – it’s literally the friction between the air and the skin or aero-suit of a cyclist. Pressure drag, on the other hand, is the difference between the high pressure at the front of the cyclist and the lower pressure at the rear. This delta is mainly caused by flow separation & vortices behind the cyclist, which reduce the pressure recovery. These forces hold the cyclist back when going at higher speeds. When riding a bike on a levelled road, around 90% of the resistance is the result of aerodynamic drag. Because a cyclist is a bluff body (a non-streamlined object), of that drag, about 85% is pressure drag and the other 15% is skin friction. Although 15% is not negligible, the pressure drag is the most important factor. That is why the focus is on optimizing the shape of components & athlete position, rather than minimizing the skin friction.
Aerodynamic testing at Team DSM
Our main techniques are track testing and wind tunnel testing. Track testing involves the cyclist tweaking his position while doing laps on a track. Obviously, it’s very important to keep the power output constant and to ride the exact same line lap after lap, which is a clear drawback of this technique. Not every cyclist can perform this test accurately. Wind tunnel testing on the other hand allows you to improve small details, as it is such a controlled environment. The biggest downside of the tunnel, however, is that you’re working on a fixed position most of the time. Keep in mind that the tests described above are done in ideal circumstances. There is no influence of any natural wind or rain. For this reason, outdoor testing is on the rise to analyse the effect of aerodynamic devices. This provides more accurate results than the wind tunnel or track testing. Our partner TU Delft developed an outdoor testing technology called The Ring Of Fire, a system in which a cyclist rides through a “ring” of helium bubbles. The motion of these bubbles is then tracked using a PIV (Particle Image Velocimetry) system as the flow pattern around the rider moves the bubbles.
The Ring of Fire - TU Delft
Being able to perform PIV measurements in open air allows us to get more information about the aerodynamics of the individual cyclist, but also to learn more about which team tactics to implement in TT (Time Trial) and TTT (Team Time Trial) for example. Each type of testing has its own upsides and downsides. Which kind of test we do, depends on which data we want to get out of it. So in conclusion, we can state we use a combination of different techniques throughout our search for optimal aerodynamics.
Aerodynamics meets biomechanics
When a new cyclist arrives at our team, he always gets a bike fitting first so the rider will not get injured during training. Afterwards, we look for the sweet spot between his biomechanics and aerodynamics to achieve the best performance. Our team aims to have the best specialists of each field work together as one team – each opinion is equally valuable, without one person taking the lead. This ‘one team, one goal’ philosophy will eventually lead to the best possible performance of our cyclists.
The science behind cycling aerodynamics
At our team, everything is science-driven. That is why our team searches for the best specialists in every field. As far as I know, Team DSM is one of the few teams which work like that. Most teams will have someone on board looking at the aerodynamics, but most of the time that person will have a background in biomechanics or sports performance. They certainly know how to make a cyclist go faster, but with my aerospace engineering background in aerodynamics the goal is to take things to the next level. And I’m very grateful to be in that position!
Via new production techniques, crazy positions and innovative measurement systems, cycling aerodynamics have come a long way. The continuous search to improve even the smallest aspects will never end. We are very thankful to Team DSM and Harm Ubbens who was willing to share his knowledge with us.
Interesting links: Interesting links:Team DSM
Cycling: From 3D scan to aerodynamic analysis
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