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We don't dabble in aerodynamics, but ...

by Carl Brewer last modified 2009-09-09 22:58

Just to show that aerodynamics is a very fickle and often counter-intuitive thing ...

Roadies don't care much about aerodynamics, most of the time they're drafting.  MTB riders aren't going fast enough to care.  Time trialists and sprinters care a lot.  At aboc, we don't pretend to know much about aerodynamics, we prefer to claim that the only way to tell if something is aerodynamic is to test it and that many things that look fast aren't necessarily so.

So, here's something that took me by surprise.  Pedaling makes very little difference to drag, at least within the confines of this test (~13m/s, ~45km/h).  Here's a paper on it.  Intuitively, it seems obvious that pedalling faster would add more drag to the bike. 

Pedaling cadence showed little effect on the measured aerodynamic drag, with only a 1% variation between test conditions. Thus, any desired pedaling cadence can be used for wind-tunnel testing.

The drag measured for a rider when pedaling is not influenced in a significant way by the speed of pedaling, in the 40-100-rpm range. The drag measured while the rider is pedaling turned out to be a little smaller than the average of measurements taken with the rider's feet stationary at various positions around the pedaling circle. We do not know the reason for this difference, but it is quite small. We conclude that it is valid to take wind-tunnel drag measurements with the rider pedaling anywhere in the 40-100-rpm range.

So there you go.  40rpm, 100rpm ... no big difference in drag.  Not what I would have thought!  Aerodynamics ...

219 RPM?

Posted by Dino Apolito at 2009-09-09 23:42
Now that's depressing. Yet another excuse I have to cross off the list.

So you're telling me the pain in the legs I feel during Tuesday nights efforts can't be blamed on the wind???

Dunno ..

Posted by Carl Brewer at 2009-09-10 00:59
One of the things it's not safe to do is extrapolate from an aerodynamics study to something outside of the test. Maybe 200+rpm does have a different drag profile to 100rpm? They didn't test it so who knows?


Posted by Neil Robinson at 2009-09-14 22:23
they do actually go fast enough for drafting to make a difference, but personal aerodynamics has to take a back seat to other factors.

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