Cycling aerodynamics
The drag force acting on a cyclist (or indeed any object) is defined as follows;
Air density reduces as temperature increases, as shown in figure 1. Therefore, raising the temperature inside the velodrome will reduce the drag force acting on the rider, allowing them to go faster. Figure 1 shows how temperature effects the drag acting on a track cyclist using typical values for the area and drag coefficient.
Reducing the resistive force acting a cyclist will give the greatest time advantage on longer distance events, such as the individual pursuit which is raced over 4 km. An in house track cycling research tool, developed by Dr Rich Lukes, was used to predict the effect of increasing the air temperature in the individual pursuit. Increasing the temperature from 20 degrees to 25 degrees produced a time advantage of approximatley 1.4 s over 4 km. The interesting thing to note is, the higher temperature will aid all athletes in breaking records, whilst giving them no advantage over their immediate competitors.
- Conclusion
Sports engineers are renowned for giving individual athletes or teams an advantage by improving their equipment. The engineers behind the 2012 velodrome have gone a step further by building a facility which should increase the performance of all competitors. In particular, the air temperature inside the velodrome will be higher than usual to reduce the drag force acting on the cyclists. Increasing the temperature from 20 degrees to 25 degrees would give a world-class cyclist a performance advantage of approximately 1.4 s over 4 km. My prediction, records will be broken in the velodrome in 2o12, particularly in the longer distance events.
- Tom
I think this is a very good blog entry. Both formal and informative. keep it up
A very good article indeed and very interesting to read. It’s certainly very warm in there as I was there over the weekend.
Whilst I do not dispute the reduced drag due to higher temperatures I’d be interested to know what effects a couple of other effects of the heat would have on performance.
Firstly to the actual athlete themselves and how quickly they tire in the elevated temperature. I’m sure this elevated temperature will make the athletes tire quicker than if in a cooler environment or at least surely make it harder to get the hydration levels right before the event if they are waiting around for several hours before their particular event.
Secondly the effect of the extra grip the tyres are likely to have on the track due to the increased rubber temperature and whether this would lead to any increase in rolling resistance of the bike?
I am an engineer but certainly have little expertise in this field. Would be interesting to get an answer however (I’m sure the first point might be slightly more athlete specific however).
I contacted my colleague Professor Edward Winter to see if he had any observations about Ed’s question. Professor Winter is an exercise physiologist with keen interests both in how to improve athletes’ performance (legally!) and engineering. This is what he offered:
Ed’s question is a good one.
I too was intrigued by the raised temperature in the London velodrome supposedly to improve performance of the cyclists. 25˚C usually marks the distinction between what is comfortable or tolerable and possibly adverse. True, air density reduces as temperature rises so high-speed travel has less resistance. Thermoregulation becomes even more challenging as external temperature rises. During exercise, most of our heat is lost via sweating i.e. the evaporation of sweat requires latent heat to change the liquid sweat into a gas. That heat is taken from the skin. This works especially well if air as during cycling, is moving quickly over the skin – providing the ambient air is not humid. Blood in the skin is cooled and then as it circulates, cools the interior regions of the body. However, the very act of moving is in itself, thermogenic – especially with the energy expenditures of world-class sprint cyclists. Of course, some heat helps muscles perform effectively but conversely, too much i.e. hyperthermia, reduces the ability to exercise. Cyclist’s heat dissipation is already compromised because their clothing reduces the area of exposed skin. What I am getting to is a trade off: the ergogenic effect of the warm air must somehow produce hyperthermia. There is of course an easy way to find out how successful the raised ambient temperature will be: time will tell. In a few months, we will know!
Good article. I have some questions. How is the lower wind resistance effected? Is it because air is less dense on the track because hot air rises? Would that then mean there also less oxygen intake per breath for the cyclist at the track level? Would you then predict that world records would be broken in sprint races rather than the long distance ones? And if the intention of the raised stadium temperature is to get world record times, would it not be better to set different temperatures depending on the length of the race rather than just setting the temp 5 degrees higher (ie. higher temps for sprints, lower temps for long distances)?
Technical note: since writing the blog it has come to my attention that the track temperature will be a constant 28 degrees C. As this is higher than my initial estimate of 25 degrees C the effect of drag will be even larger.
. . . and so too will be the thermoregulatory challenge.
An exiting article from a sports engineering perspective. Question:
Could a negative ionised air consumption be used in this “closed” invironment to give the individual, advantages in terms of breaking records, if this truly is the engineers whish?
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