CatEye PW-TR100 Power Unit - Manual (Page 55)

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PW-TR100 : POWER UNIT
Reference Guide
Power meter training manual for Cateye
What is power?
Training with power is an important and exciting way to monitor and improve your cycling performance.
For any given conditions your bicycle speed will be greater with a higher power output. Unlike heart rate,
which is a dependent variable and can vary due to external influences (such as diet, fatigue, and ambient
temperature, etc.) power directly affects your performance.
Simply, power can be expressed as the total of all the force that must be overcome to move you and the
bike. Power is measured in watts (W), and can be loosely described by this equation:
Power = velocity x (air drag + rolling resistance x mass of rider and bike + gradient of road x mass of
rider and bike + kinetic energy)
Aerodynamic drag is determined by the frontal area of the cyclist and bicycle (height, width, and shape/
position of bike and rider), and equipment that is being used by that rider (e.g., disc wheels, tri-bars, etc).
Additionally, environmental conditions (i.e., air density which is determined by temperature, barometric
pressure, altitude, and humidity, and wind velocity) also affect aerodynamic drag.
Power output can also be mathematically expressed via a number of equations, and is defined as
Power = work done/time or Power = torque x velocity
In the case of the Cateye meter it is the torque (angular force) multiplied by the bottom bracket velocity
(cadence). Thus, power output (W) = torque x cadence