Rider Aerodynamics (Fit and Positioning) Power Use breakdown*
% of Total Power Consumption:
Rider Aerodynamics: ≈50% of total power use (75% of total aerodynamics)
The bottom line: If you are on a solo ride and average 20 mph over a 100 miles of varied terrain, lowering aerodynamic drag by 10%, without changing power output, will cut 21 minutes of time (7%). Time will drop from 5 hours to 4 hours and 39 minutes and average speed will go up to 21.4mph. Getting comfortable in an aerodynamic position that you can maintain offers big benefits.
How to go about minimizing the negative effects: Get fit properly to minimize your drag first and foremost. If you are a road rider in a pack, use others to your advantage. If you are a Time Trialist or triathlete, at the minimal, be sure you are using aerobars that are set up well for you and comfortable. If you cannot hold an aerodynamic position, it cannot work for you. From an equipment standpoint, the front of the bike (fork, head tube, handlebars, cables and front wheel), and how clean it is set-up, are most important. These are the items that break the undisturbed air first. Visit the bicycle aerodynamics section for more details on the concepts and terminology of cycling aerodynamics.
*Studies have not been completed with enough accuracy to show the exact importance of all variables in relation to each other. Results are taken from a variety of studies.
Explanation and Tech talk:
After reading the many magazine ads and articles focused on lightweight and aerodynamic bikes and parts, you would think these are what you should first focus your attention on. However, unless you are just climbing hills, weight is of minimal importance – cutting a monumental 5 lbs. of weight off your bike will get you across the line about 200 yards (a whopping 1/40th of 1mph of average speed) earlier over a 100 mile mixed terrain ride. Meanwhile, your bike’s aerodynamics is about 25% of the vehicle (bike and rider) total aerodynamic package – the other 75% of aerodynamics is the rider. Therefore, the rider’s aerodynamics and comfort are closely linked and crucial to your overall performance and aerodynamic efficiency on the bike. As an example:
At the end of 1999, the UCI made modern aero equipment illegal for hour record attempts. They reinstated Eddy Mercx’s 1972 record and stripped Chris Boardman of the mark he had set a few years earlier using modern aero equipment and positioning. At the end of 2000, Chris Boardman followed the “new” UCI rules to reclaim the hour record. He used a similar position and a similar sub 14lbs bike to the what Eddy Mercx used in 1972 and beat Eddy’s record by about 12 meters. Much more notable, however, was that Chris Boardman didn’t even come close to beating the record that he set using modern aero equipment that the UCI stripped from him at the end of 1999. Chris’s earlier, “assisted”, hour record distance was close to 3 miles further than the mark he set unassisted in 2000! That means his average speed was 3 mph slower than the “assisted” record he had set a few years earlier. Equally notable is that the “assisted” record he set in the mid 1990’s was done riding a 24.5lbs (about 10 lbs heavier!) aero bike in a modern aero position. That is how important aerodynamics is. Over 10 lbs heavier, yet his average speed was 3 mph faster.
You’re not trying to break the hour record, so what does this have to do with the products you choose? The comfort related aspects (especially the fit and vertical compliance/comfort) of the products you choose will play a large role in how well you stay aero and efficient.
It takes very little increased surface area to drastically slow a vehicle. Consider how an airliner’s wing flaps or landing gear can slow such a large vehicle. You can physically feel a significant shift in air speed when the relatively small landing gear is dropped. If you have to sit up in the saddle, even just ½ an inch, each time you come upon a bump or other surface variation in the road, you end up acting like a parachute and scrubbing speed. Considering it takes more energy to accelerate than anything else, scrubbing this speed and then having to reconstruct it is a really large drain on your energy reserves and efficiency. This is why it is really important to think about aerodynamics from a full vehicle, not just bike, perspective. Do not buy products just because they are aerodynamic on their own. These products might be so brutally stiff and transmit so much road vibration that you cannot stay aerodynamic as you try to ride them. It is also worth some serious consideration when choosing your wheels as well.
For additional information on aerodynamic concepts in detail and an aero glossary, visit the bike aerodynamics section.