Aerodynamics? Isn't that more for roadies? Yes and no. On the road, air resistance is almost always dominant because the tyres find less resistance. But the same laws of physics apply to biking: On hard surfaces, air resistance is the dominant driving resistance from 16 kilometres per hour, and it also increases cubically with speed: riding twice as fast requires eight times more power! EIGHT TIMES! Hardly any biker can manage 40 km/h on the flat, even if the surface is the finest tarmac. This is mainly due to the miserable aerodynamics of bike and rider. Of course, you intuitively realise that baggy shorts and flapping shirts are not good for speed. But what slows you down and how much is not necessarily obvious just by looking. That's why we placed a rider and bike in the wind tunnel and checked various positions and outfits with sensitive measuring technology.
The bike is fixed to the wind tunnel balance and the wheels are brought up to an inflow speed of 35 km/h via rollers in the floor. We measure the force that the wind exerts on the bike and rider and can thus determine the power requirement for this speed. We determine 71.4 watts for the naked wheel. With a rider, the resistance of the system increases to up to 271 watts (sitting upright and wearing flats, positions 1 and 2, see next page). To ride at this speed outside, you also have to overcome the rolling resistance, which is a further 52 watts for a very fast tyre. In total, 320 watts are required for a speed of 35 km/h, 85% of which is due to air resistance. To accelerate to 40 km/h, 462 watts would be required - no professional can manage that in the long term.
You can find out how the seating position affects you in different wind forces, taking into account your clothing, in the test, which you can download as a PDF below.
Annika Langvad reaches for the fork crown to keep up the pace at the Cape Epic. The streamlined position is essential to reduce the air resistance in the leading position, as the rider herself brakes far more than her bike. Her team-mate Kate Courtney saves even more energy in the slipstream. But even off the racetrack, if you want to ride fast, you have to sit streamlined and wear tight clothes. Baggy shorts and flutter shirts? You have to be able to afford them, they are brake parachutes. Our insider tip for marathon racers: dropper posts! They not only give you an advantage on steep sections, but also help you pick up speed on harmless descents.
You can find this article in BIKE 8/2020. You can read the entire digital edition in the BIKE app (iTunes and Google Play) or the print edition in the DK shop reorder - while stocks last:
