iBike Gen III Operating Instructions Manual page 58

Crr (coefficient of rolling resistance) measures the amount of opposing friction caused by
road surface, tire type, and bearing friction. A low value of Crr means low rolling
resistance.
On a very smooth surface, such as those found at an indoor track, Crr can be 0.003.
Asphalt roads have a typical Crr of 0.0055, and dirt roads can have Crr values of 0.008 or
higher.
Values of CdA and Crr can be measured by the Coast Down procedure, or they can be
estimated accurately as part of the Fast Start sequence.
WHAT DOES "HEADWIND" MEAN?
The headwind speed that is displayed by your iBike is the TOTAL magnitude of wind
blowing directly in your face as you pedal. A few examples make this easy to understand:
You ride at 15mph directly into a 12 mph headwind. The iBike will read 27 mph
•
headwind.
You're going 18 mph and there is a cross wind of 10 mph. The iBike will display 18
•
mph as the headwind (remember, you're riding perpendicular to the wind's
direction.)
You're going 20mph and there is a tailwind of 10mph. Your iBike reads
•
10mph as the headwind (it knows you're getting a bit of a free ride from
mother nature!)
NOTE: WITH "ABS WIND/YES" YOUR IBIKE WILL REPORT THE ACTUAL WIND SPEED.
UNDER WHAT CONDITIONS CAN THE IBIKE BE "LESS ACCURATE"?
There are two extreme riding situations where it is difficult for the iBike to measure watts
with highest accuracy:
1) Sharp turns such as hair-pin turns. During sharp turns when your handlebars are
pointed into the turn your watts may read low. As soon as the turn ends your watt readings
will return to full accuracy.
2) When pedaling at high speed in a tuck. While pedaling on downhills, any minor
variation in ride position from your normal ride position (such as going into a tuck to pick
up more speed), or any error in your drag coefficient measurement, can cause a false watts
reading. The reason is simple: wind resistance varies as the cube of your speed, so high
speeds "amplify" enormously the watts errors caused by ride position changes. As a
practical matter, most riders DON'T pedal on downhills (it's a very poor use of rider energy)
and when not pedaling, any iBike with a cadence mount will report zero watts.
WHAT CAN I DO TO GET THE MOST ACCURATE RESULTS FROM MY IBIKE?
Your iBike will work extremely well when it is properly calibrated:
1) Perform the Fast Start sequence AND the Cal Ride. For the highest level of
accuracy, you may also perform multiple Coast Downs after completing the Cal
Ride. Make sure to use the iBike software to analyze your Cal Ride/Coast Down
data.
2) If you don't pedal on down hills, the cadence sensor will force watts to zero
whenever zero cadence is detected.
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