Author Topic: Wheel Cover Aerodynamics  (Read 2994 times)

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Quel

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Wheel Cover Aerodynamics
« on: May 11, 2011, 11:36:06 PM »
Not sure if any of you get Wheelbuilder.com emails and have seen this, but I thought it was interesting.  Plenty of people have said that a plastic wheel cover is just as aero as an expensive carbon disc, but here's some data to support it finally.


ijen

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Re: Wheel Cover Aerodynamics
« Reply #1 on: May 12, 2011, 12:13:19 AM »
30 mph  :o

shovelhd

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Re: Wheel Cover Aerodynamics
« Reply #2 on: May 12, 2011, 09:07:34 AM »
30mph is the sweet spot in bike racing, when the pace strings the field out, the start of the sprint, etc...i.e. when it counts. I don't know what a detriment it would be in a crosswind. There is at least one team up here that rides them in road races and crits.

rm -rf

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Re: Wheel Cover Aerodynamics
« Reply #3 on: May 12, 2011, 09:21:24 AM »
It reports drag in grams.   How would that convert into watts?

Offline <gmt>

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Re: Wheel Cover Aerodynamics
« Reply #4 on: May 12, 2011, 10:02:33 AM »
this comes from Coggan on slowtwitch


0.1 lbs (50 g) of drag (at 30 mph) = 0.5 s/km = 5 W = 0.005 m^2 CdA = 0.0005 Crr

The above rule-of-thumb (which refers to changes) is based on various assumptions/rounding everything to a 1 or a 5, but is fairly accurate and hence quite handy when doing in-your-head (or back-of-the-envelope) calculations.
o-meter

EDR

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Re: Wheel Cover Aerodynamics
« Reply #5 on: May 12, 2011, 11:27:19 AM »
I'm a little confused , how can a covered wheel have any better aero as yaw increases?  The 30mm alloy covered wheel has zero drag at 20* yaw?  Something ain't right about this.

Quel

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Re: Wheel Cover Aerodynamics
« Reply #6 on: May 12, 2011, 12:18:04 PM »
Zipp's own tests show their discs having low/zero/negative drag at those higher yaws (http://www.zipp.com/_media/pdfs/technology/revolutionary_speed.pdf),  so it's not unique.  This test doesn't show the Zipp disc getting there, but it's close.  I'm not sure of the exact science behind it, but you get a bit of a sail effect from the wind that cancels out some of the drag.

WheelBuilder says this:

"The lens-shape on a disc-cover's non-drive side causes wind to pass around it like a wing, producing forward thrust. This effect is more pronounced on covered shallow wheels beyond 20 degrees of yaw."

EDR

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Re: Wheel Cover Aerodynamics
« Reply #7 on: May 12, 2011, 12:27:03 PM »
Thanks.  That's interesting stuff, kinda makes me think of getting a Stinger 9 and a cover.  This would give me one wheel with a dual purpose, uncovered/crits covered/TTs