Asker Jeukendrup: Real World Aerodynamics
Whether you are a beginning time trialist or a world class competitor there are several ways to use aerodynamics to your advantage. Some are relatively inexpensive while others are prohibitively expensive. We got the inside scoop from noted exercise physiologist Dr. Asker Jeukendrup…
Dr. Asker Jeukendrup is one of the top exercise physiologist investigating the metabolic responses to exercise. He has served as the scientific advisor to the Rabobank professional cycling team, and edited High Performance Cycling, a book compiled to translate cutting edge scientific research into recommendations for cyclists of all abilities.
Following on our interview last year with Scott Daubert of Lance Armstrong’s F-One team, we caught up with Dr. Jeukendrup to analyse the findings from his 2001 review paper (co-authored with Jim Martin, Ph.D.) modeling the aerodynamic improvements from various changes in equipment and positioning (1). The modeling might surprise those of you considering that extra bling lightweight aero gizmo…
You Can’t Be Fast if You Can’t Pedal!
First and foremost you should invest the greatest amount of time, energy, and financial resources into your training. With a 7-8 min improvement from training, it’s a cold hard fact that if you can’t pedal hard enough no amount of wind cheating aerodynamic equipment will make much of a difference.
Secondly, roughly 70% of the drag numbers seen in a wind tunnel are rider and position related. Therefore you will cheat the clock the greatest by dialling in your best possible aerodynamic position on the bike. The model predicts a 2-2.5 min improvement from optimising your position. From a cost/speed ratio this is the cheapest and most effective way to improve your time trialing under the same power output.
However, it is important that you are able to sustain power in an aerodynamic position. As always, specificity is the key and it is critical that you practice on your TT bike or aero position to adapt to it.
FO: Training aside, how should amateur cyclists spend their time and money to improve their time trial performance?
Dr. AJ: These estimations are for a 70 kg rider with a VO2max of 55 ml/kg/min, and a peak power of 300W. (FO: As you can see you’ll be able to sustain a higher speed by improving your engine first and your machine second)
FO: How about this: On a rolling 40 km time trial (no change in altitude from start to finish), how much difference does it makes to change the weight of your bicycle by 3 kg (6.6 lbs) versus losing 3 kg of body weight ?
Dr. AJ: For our simulations we use a standard course. The time trial (TT) course that our imaginary cyclists are going to ride is exactly 40 km and is an out and back course. The out stretch has a constant tailwind of 2 m/s and one hill with a 5 km long constant 1 % gradient followed by a 5 km 1% downhill. The hill is followed by a 10 km flat section to the turn around. We assume that the riders do not have to brake or accelerate to make it round the turn before returning along the flat and over the hill with a 2 m.s-1 headwind. The riders do not sprint or fatigue and cycle with a constant power output for the entire duration. In the baseline condition riders have 10 kg bikes and a standard aero position, they use aero wheels and only drink water. In these conditions the riders would record times of 1:12:56 (h:min:s). It is interesting that, compared with the 10 kg bicycle used in the baseline calculations, the 3 kg lighter bicycle would increase average speed by only 0.1 km/h for all our riders. This is despite the simulated course involving 10 km of climbing up a 1% gradient! If these improvements are compared to those achieved with aerodynamic wheels then the importance of bicycle weight on performance over a relatively flat course can be put in perspective.
FO: As a recent purchaser of a time trial frame I have to admit I was confused about the difference between a time trial specific frame with one seat tube angle and the seat tube angle on my road bike. Would you break it down for the amateur cyclist who spends the majority of his time riding his road bike?
Dr. AJ: It is very important to note that we can get riders in incredibly aerodynamic positions but they are not able to produce any power in those extreme positions. Riders often comment on this when going from their road bike to a time trial bike with different seat tube angles. The reason for the different seta tube angles is to rotate the cyclist forward in order to reduce frontal area and aerodynamic drag. However, this usually means a position that is less comfortable and in some situations may compromise power. If the benefits of being more aerodynamic outweigh the disadvantages (back pain, reduced power) it is worth doing. In the windtunnel tests we did we sometimes made changes to the rider’s positions that did not make them more aerodynamic but enabled them to produce more power for longer.
FO: The balance between a light and aerodynamic bike is a very complex relationship. When should cyclists give priority to aero wheels over lighter, climbing wheels?
Dr. AJ: If a course is flat there is no doubt that the advantages of aero wheels far outweigh the effects of ultalight wheels. If 3 kg is not going to make a big difference, 100 grams certainly isn’t. When going uphill this becomes a slightly different story although as long as speeds of 15 mile/h can be maintained aero wheels will still have an advantage. When speeds go down to very low numbers, usually when the hills are getting very steep, that is where a lighter bike or lighter wheels may outweigh the advantages of aero wheels. On a 7% grade many riders can still ride fast enough to take advantage of aero wheels.
FO: Thank you very much for your time and your expertise. Is there any parting advice you would like to give to the time trialists in all of us?
Dr. AJ: Before spending loads of money, sort out your body position. Windtunnel testing is expensive but there are cheap alternatives on offer. The cheapest way is to find a hill with good road surface. Start at the top in position A, do not pedal and time how long it takes to get to the bottom. Then climb back up, make a change to your position and do it again. If you do this often enough you will get a reasonable idea of what is aero and what isn’t.
FO: Finally, for fun, would you care to comment on Lance and the hour record?
Dr. AJ: If Lance is going to ride, the record will be trashed. If Lance is going to do this he will only do this with optimal preparation, he will get the best possible team together to make him as aerodynamic as he can possibly be and he will be in optimal shape, having the optimal nutrition and psychological preparation. Such an Armstrong is unbeatable. And it will be a pleasure for us to watch!
1. Jeukendrup, A. E. and J. Martin. Improving cycling performance: how should we spend our time and money. Sports Med. 31:559-569, 2001.
Frank is a USA cycling certified Expert coach, category 1 road racer, and bronze medal winner in the 2004 Colorado State Time Trial. To find out how you can time trial at your best visit his website