On 12 May, 20:48,
[email protected] wrote:
> On Mon, 12 May 2008 10:56:30 -0700 (PDT), Robert Chung
>
> <[email protected]> wrote:
> >On May 12, 10:23 am, "Rik O'Shea" <[email protected]> wrote:
>
> >> I used the Dublin port tunnel just before it was opened to traffic for
> >> a very successful set of CdA field tests (it was just about to be used
> >> for a 10 k running race).
> >> Its perfectly flat, at sea level, over 4 km long and there is zero
> >> wind in it!
>
> >Could you describe your test protocol and how you could tell that they
> >were very successful?
>
> Dear Robert,
>
> I'm curious, too, since detecting the kind of differences that seem to
> be involved should include weighing the rider and checking the tire
> pressures before each run, as well as recording the temperature,
> humidity, and barometric pressure.
>
> As for the actual wind speed, many posters in this thread may be
> unaware of comments like this from Andy Coggan:
>
> "More recently, I've conducted three days of testing using Lim's
> approach of multiple speed trials to separate CdA and Crr...despite
> doing the testing very early in the morning on very flat roads,
> precision was again only about 2%. One impressive finding from these
> experiments was how little wind it takes to really skew the results -
> for example, on a day so calm that a tiny piece of dry leaf dropped
> from overhead falls to the ground less than 1 foot from vertical,
> there are still significant differences in estimated CdA depending on
> whether you are headed 'upwind' or 'downwind'. Similarly, trials
> conducted less than a full minute after a vehicle passes down the road
> at ~30 mph also produce abnormally high or low values, depending on
> whether the trial was in the same direction or the opposite direction
> in which the vehicle passed."
>
> http://groups.google.com/group/rec.bicycles.racing/msg/060f5e7d17060960
>
> Cheers,
>
> Carl Fogel
Here's the Required Test Conditions
(1) Select an appropriate test course; this can be a “speed trap” i.e.
a section of road between 200m and 1000m long or a velodrome. The
speed trap dictates that you should have reached your desired steady
state speed before you enter the start of the trap. This speed is
maintained while in the trap (i.e. there should be little or no
acceleration). As you exit the trap and end your test run your speed
should be the same as when you entered the trap. The advantage of a
longer speed trap is that it may allow slight fluctuations in speed,
power and wind to be averaged out allowing a more accurate average
power and speed to be recorded.
(2) The course should be flat with no corners. The road or track
surface should have minimum variation in texture; smooth or even
surfaces provide the best results.
(3) Calm wind conditions should exist. A 30 cm length of single-ply
tissue paper held hanging straight down reveals whether or not calm
wind conditions are prevalent.
(4) The course must be free from interference from road traffic. You
should wait at least one minute after a vehicle passes before
performing a test trial.
All these conditions were met in full - in particular (3) which is
difficult in an open air course.
Here the exact protocol
(1) Record the total mass of rider + bike
(2) Record the air pressure, air temperature and humidity - used to
calculate air density.
(3) Perform the desired number of test trials recording the average
speed and power (the complete series of test trials took less than 30
minutes).
- Use a fixed speed rather than power for each test trial.
- To start choose speeds with roughly equal intervals. At higher
speeds the interval can be progressively decreased.
- The order of test trials involving various speeds should be
randomized. This is optional.
- Before you enter your speed trap or start your recording interval
you should have achieved the desired steady state speed. You should
strive to maintain a steady speed for the duration of the test trial,
i.e. no acceleration or deceleration.
- Maintain the exact position on the bicycle for each trial.
(4) When you have completed the field test use your power meter
software to extract the data for each test run i.e. to select the
starting and finishing points of each interval so that the start and
finish speeds are equal. Then obtain the average speed and power for
each test run.
This protocol was followed exactly and the results had a very high
statistical significance.
