(Sorry about the previous screw-up!)
Very interesting! If I use our model of the power requirements of
cycling and John Cobb's wind tunnel data for the Corima wire-spoked
wheel and the Rolf Vector Pro (the only two wheels tested by both),
here's what I get:
Corima wheelset:
Power = 384 W (measured by Tour magazine)
Calculated total aero drag @ 30 mph (20 deg C, zero wind) = 7.02 lbs.
Rolf Vector Pro wheelset:
Power = 407 W (again, measured by Tour)
Calculated total aero drag @ 30 mph (20 deg C, zero wind) = 7.48 lbs.
IOW, based on the Tour data and our model, using Corima wheels instead
of Rolf wheels reduces your overall drag by 0.46 lbs, or 0.23 lbs/wheel.
This corresponds almost EXACTLY with what John measured in the wind
tunnel: average drag for the Corima wheel at 0 to 10 degrees of yaw was
0.16 lbs, whereas the average drag of the Rolf wheel at 0 to 10 degrees
of yaw was 0.38 lbs, a difference of 0.22 lbs.
I also did the calculations for the SPOX R2 wheelset (which to my
knowledge John has not tested in the wind tunnel):
SPOX R2 wheelset:
Power = 413 W (again, measured by Tour)
Calculated total aero drag @ 30 mph (20 deg C, zero wind) = 7.60 lbs
Thus, the SPOX R2 wheelset apparently generates 0.12 lbs more drag than
the Rolf wheelset, or a difference of 0.06 lbs/wheel. This is about
one-half of the 0.13 lbs difference that John found for the original
SPOX, which lacked the R2's aero rim.
I think the above calculations support several conclusions:
1) w/ care, testing of wheels on an indoor velodrome and a power
measuring device can give reasonably precise results.
2) our model is able to predict fairly small differences in overall drag
with good accuracy.
3) extrapolation from results of wind tunnel testing to the so-called
real world is (as expected) valid.
4) the fat SPOX found on the Spinergy wheels create additional
aerodynamic drag, just as you'd expect.
(Note: for the above calculations, I assumed a bike + rider weight of
183 lbs, and a oefficient of rolling resistance of 0.003, but these
assumptions - and the others listed above - have very little impact on
the overall conclusion. The use of drag data averaged over 0 to 10
degrees of yaw is justified on the basis of Project 96 measurements
showing that yaw angle varies over that range as one circles a
velodrome.)
In article <871z4bk...@nuc04.t30.physik.tu-muenchen.de>,
Emilio Lopes <Emilio.Lo...@Physik.TU-Muenchen.DE> wrote:
> Following table shows the power needed to sustain a velocity of
> 45 Km/h for some current aerowheel sets. The numbers are from the
> German magazine "Tour" (April 2000). The tests were carried by a
> professional rider using an SRM-equiped bicycle in a track.
>
> Wheel Set Power in Watts (for v=45 Km/h)
>
> Corima 4-Spoke HM 381.9
> Corima Spokewheel 384.5
> Lightweight 385.0
> Citec 3000 390.0
> Mavic Ksyrium 391.8
> Zipp 530 394.7
> Ritchey OCR 395.7
> Shimano Dura Ace 399.7
> Rolf Vector Pro Carbon 407.0
> Spinergy Spox R2 413.3
>
> I don't know why Campagnolo's Shamal or Bora were not tested.
>
--
Andrew Coggan
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Before you buy.