Partnered Devices Create Cycling First
ANT+ Alliance member product partnering resulted in unique, advanced application.
Velocomp’s iBike is a good example of sensor interoperability with ANT+. Velocomp’s innovation resulted in the ability to measure CDA in real time by receiving bike power from another ANT+ power sensor and calculating the drag area in real time. This means of measurement has never been available to riders previously as costly wind tunnel testing has been the only option up until now. The interoperability of ANT+ device network has allowed this creation of a unique and advanced sensor application.
When riding against the wind, the amount of wind resistance a rider experiences is heavily dependent on how "aerodynamic" the riding position is. The measurement of aerodynamic resistance is called CdA (coefficient of drag times frontal surface area). The lower your CdA, the easier it is to move against the wind and the faster you'll go, even with the same number of watts produced. Minimizing drag allows you to maximize the speed you can maintain for a given power output.
The iBike is a unique device because it measures the forces opposing the rider (such as incline and wind resistance) rather than making a direct measurement of the force the rider is putting on the driveline.
Calculating bike power requires input from ANT+ wheel speed and cadence sensors (available from Velocomp and other ANT+ compatible devices) with compatible sensors by ANT+ Alliance products such as the Garmin Edge 705.
An important value for iBike’s computation of bike power is the rider’s coefficient of drag area (CDa) - a value which is calibrated from coastdown tests performed by a rider as part of the iBike setup. When calculating power, CDa is assumed to be constant, although changes in rider position will actually affect this value constantly.