Garmin and Look/Polar are simultaneously launching an entirely new generation of power meter based in the pedal axle.
After years of rumors, development, cooperation between two companies and a merger by another, pedal-based power meters are finally (almost) ready. Polar and Look teamed up to create the Keo Power system and Garmin purchased tech start-up Metrigear to develop Vector, their own power meter. Both units are scheduled to be ready for sale in the spring of 2012. Garmin’s unit will be released in March and Look/Polar will have them ready in January.
There are a few potential benefits to the pedal-based format compared to the current hub- and crank-based power meters.
First, they can be swapped between bikes without changing a major component.
Second, they can measure power when riding different wheels. Hub-based power meters cannot.
Third, they provide the power split between the left and right legs.
Fourth, they can measure force produced by the rider that never makes it to the drivetrain.
But measuring power through the pedals introduces complications that crank and hub units do not have to overcome. Power meters measure the deflection of a component and its velocity to find the rider’s power. All flex in the hub and crank is created by power actually directed into the drivetrain. But the pedals are not only flexed when the rider pedals, but when the rider stands on the pedals. The pedal power meter systems must differential actual pedaling power from the forces created by the rider leaning on the pedal or bouncing on the pedals while riding over rough surfaces. The spindles measure force, but force is only part of the equation for rider power. The other component is velocity. To measure actual power rather than force on the pedals mistaken for power, both units use accelerometers in their external transmitters to measure pedal velocity (cadence, which means the rider is actually pedaling), and the transmitter pieces must be fixed almost exactly perpendicular to the crank arm to accurately measure power.
Details about Keo Power and Garmin Vector on pages two and three.