The claim sounds bold: 58 to 75 seconds per hour - that's how much time the bike manufacturer Felt promises to save on its AR 0 aero racer compared to a racing bike with a round tube frame. Around a minute faster per hour - that's a world of difference in top-class sport, and not to be sneezed at for strong amateur cyclists. If the calculation is correct, classically shaped racing bikes would suddenly look pretty old. And Felt is neither the first nor the only manufacturer to use aerodynamics as a sales argument. Cervélo's Soloist can be regarded as the founder of this trend, and other suppliers have since followed suit - and others are sure to follow. So does this mean saying goodbye to the idea that the best road bike "only" has to be light, stiff and comfortable? Do aerodynamics now also count for normal road racers? This does not seem entirely absurd. After all, air resistance is and remains the cyclist's biggest opponent. A rider has to invest up to 80 per cent of his power just to overcome it. The insidious thing is that the power required to overcome air resistance increases to the third power with speed - twice the speed requires eight times the power! So it seems only logical to analyse the aerodynamic quality of the bike. After all, at top speed in a race, even the smallest advantage can make the difference between victory and second place.
On the other hand, statements such as Felt's must be met with scepticism. In contrast to clearly defined bodies such as cars, bicycles are extremely difficult to measure from an aerodynamic point of view. A different rider, different wheels, a different frame size - and the cd value, which describes the aerodynamic quality of a body, changes. It is therefore almost impossible to make binding statements about time advantages. Each measurement result only applies to the configuration of rider and bike measured in each case. In addition, the frame only has a small influence on the aerodynamics within the overall system of rider and bike, while the rider alone contributes around 75 per cent to the overall drag. Despite this diffuse starting position, it is of course exciting to see how big the influence on aerodynamics actually is. So it's high time for the first comparative wind tunnel test to clarify the most important questions: What advantages in watts do aerodynamic frames offer over round tube frames? And what compromises do the manufacturers make in terms of weight, stiffness and comfort? Based on our experience from the last wind tunnel test of time trial bikes (TOUR 2/09->), it was clear that the only way to achieve reproducible results was to use a test setup with a dummy driver. A live driver causes too many measurement errors because even the smallest movements and changes in position influence the result. As suitable dummies are not available off the shelf, a test pilot had to be built before the measurements could be taken.
You can find the test results in the PDF download below.
Photos: Markus Greber, Daniel Kraus, Robert Kühnen
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