Copyright Velocomp LLP 2005-2013
21
“COAST DOWN” PROCEDURE
When you ride at high speed the effects of wind, bike aerodynamics, and riding
position become very significant. These effects are measured by aerodynamic drag,
commonly called CdA.
Using Isaac, or using the Fast Start sequence in your , provides accurate
estimates
your CdA. The estimates of CdA made by the are the result of
considerable testing and experience.
For 99.5% of riders, Estimated CdA and Crr provide
both consistent and very accurate results under nearly all cycling conditions
.
If you do solo rides on the flats at speeds consistently above 23 mph, or you want to
measure your CdA (and, optionally, Crr), then the coast down procedure is an advanced
feature that is available.
The coast down calibration found in the User sequence
measures
the aerodynamic (and
optionally, friction) drag coefficients that are particular to each cyclist, riding position, bike
type, tires, and road type. These drag coefficients are stored in the ’s memory (in
a Profile) and are used in power calculations.
The coast down procedure is this: accelerate to 20 mph (32 kph),
then stop pedaling
. Your
bike will slow due to aerodynamic and frictional drag (your bike may also slow due to the
effect of hill slope, but the factors hill slope effects into its calculations). Once
you slow to 8 mph (13 kph) the coast down is complete. For good accuracy, repeat the
coast down 5-8 times, then analyze your results in the Isaac software to get the best
composite measurements.
The Coast Down measurement works very well when the procedure is followed. However,
if the procedure is not followed EXACTLY, then it is likely that your will be more
poorly calibrated than it was prior to the Coast Downs! So, if you decide to do coast
downs, please read these instructions carefully and follow them exactly.
Here is the Coast Down procedure:
1.
Before doing Coast Downs you MUST use Isaac, or the Fast Start Sequence
in the , to provide rider information. AND, you must perform the
Calibration Ride.
2.
Wear the clothing, bike helmet, and shoes you’re going to use during your rides.
3.
Find a fairly level to uphill road,
with few cars, where you can coast on the road
for about 1/4 mile, without stopping, hitting big bumps in the road, making sharp
turns, or being subjected to wind gusts caused by passing traffic, other cyclists or
gusty wind conditions. DO COAST DOWNS ONLY WHEN WINDS ARE CALM.
NOTE
: THE ROAD MUST BE MOSTLY LEVEL TO SLIGHTLY UPHILL. IF THE ROAD HAS TOO
MUCH DOWNHILL YOU WON’T SLOW TO 8 MPH!
4.
Just before starting your Coast Down, enter Setup, then scroll to USER. If “USER
YES” is shown, click the up arrow to enter the user sequence. If “USER NO” is
shown, click the center button (to make the word “NO” flash), then select YES with
the up arrow, then click the center button to accept (“USER YES”). Then, click the
up arrow to enter the User sequence.
5.
In the User sequence, click the up arrow button until you find the “Coast” menu.
You will see the word “Coast” in the bottom window.
