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I was wondering the other day, why it always seemed so difficult to ride at a high RPM into a headwind at given power output, vs on a trainer, in a draft or with a tailwind. For example, the perceived exertion at 300W seems harder at 100 RPM into a headwind vs a tailwind. It occurred to me, that if you are riding at 20 mph into a wind of 15 mph and also having to move your entire leg forward into the relative wind of 40 mph (lets assume this is an additional 5 mph relative wind from pedal speed), then you are facing a lot of air resistance. If you are going with a tailwind at 25 and even going slightly uphill and still doing 300 W, it just seems easier to do 100 RPM, likely because the reduced air speed which this time is perhaps down to 25-15+5 ~ 15 mph.
I find that I seem to have difficulty in holding a high RPM into a headwind, and perhaps this may be part of the reason. High RPM on a trainer, behind someone or with a tailwind at high power output is not an issue, but the moment I get blasted by wind, I want to crank at 80-85 RPM.
Any thoughts ?
I've thought the same thing too devashish paul. I just got off my bike about an hour ago fighting a 16 mph Southwest headwind gusting to 22 mph. I found (as you did) that punching into it with a big gear (53/15,16)was most effective. Trying to maintain a cadence anywhere over 95 RPMs didn't get the job done. A couple thoughts:
It has been a while since I've been on my Powercranks, so my pedal stroke is not at its best. If my stroke were better I know it would be easier.
Here's a real can of worms: I have long suspected that a higher cadence is substantially less aerodynamic since the FREQUENCY of the foot, shoe, pedal, crank assembly coming over the top of the pedal circle is great and the speed at which it is encountering the boundry layer of air surrounding the bike/rider is higher. At lower cadences both speed and frequency are reduced, possibly (certainly?)lowering the "incidence of parasitic drag" and hence the corresponding turbulence in the boundry layer.
The application of power at lower cadences may be totally different (and more efficient) than at higher cadences.
Just a few ideas to get this thread rolling....
Tom Demerly
The Tri Shop.com
*Substantially* less aerodynamic?
I see your theory, it's not unlike the 650c versus 700c wheels debate, but I don't see how the effect could be significant. How do you define substantially?
That maybe so, but I wonder what the effect would be if you had to do it for an hour+ You could be cranking out bigger wattage per revolution, but that would probably add to fatigue after a while. I think it's mostly perceived. I too have noticed the phenomenon, but I think it's more a sense of accomplishment per revolution rather than an increased sustainable efficiency.
my $0.02
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Animal!!!
Uhh, Tom: please don't talk about pushing a 53/15,16 gear into a 16-22mph headwind. As one who was out in the wind today and couldn't have sustained anything near that, I humbly point out that your long hours at work haven't hurt your fitness too much!