Power Meter Comparison
PowerTap G3 Rear Hub vs. Wahoo SPEEDPLAY POWER Left Sided
We all have those rides when we wonder if it’s the power meter or our legs that are reading low. After an initial install and calibration of my new SPEEDPLAY POWER Left Sided pedals, I had the feeling that it was the power meter that was off. But my feelings are not always reality, so I went to the data.
Trainer Test: PowerTap vs. SPEEDPLAY
On August 25, after calibrating both power meters, I did a one hour ride on the trainer. The data showed a 8% discrepancy with the PowerTap recording 160 watts over the hour-long ride while the power pedal recorded 147 watts over the same ride. Having confirmed the accuracy of my PowerTap G3 Hub on several accounts, I took the data to the Wahoo tech team to problem solve.
Powertap hub reading 8% higher than SPEEDPLAY POWER Left Sided pedals: 160 vs 147 watts
I provided Wahoo with these files. They asked me to confirm that I installed the pedals with the provided pedal washers and tightened them to the recommended torque of 30 Nm. Wahoo then outlined a protocol of bedding in the pedals by completing 3 standing sprints from a stop followed by a manual calibration. This should be done any time the pedals are moved from one bike to another!
Field Test: PowerTap vs. SPEEDPLAY
On September 8, I followed the 3 standing start sprints calibration protocol and found the power meters then record nearly identical at all intensities and durations.
The set up: PowerTap G3 Rear Hub hub paired to Garmin computer and SPEEDPLAY POWER Left Sided paired to Wahoo computer
The protocol: calibration; 3 standing start sprints; calibration, proceed with field testing
Tests: Hour ride with 3 X 5 seconds; 1 X 30 seconds; 1 X 60 seconds; 1 X 10 min
Powertap hub reading within 1% of SPEEDPLAY POWER Left Sided pedals: 135 vs 136 watts
Max: 724 vs 730 W
30 seconds: 429 vs 436 W
60 seconds: 374 vs 377 W
10 min: 212 vs 210 W
Conclusion
With the exception of max power, SPEEDPLAY POWER LEFT Sided reads 1-2% higher than PowerTap G3 Rear Hub. Given a 3-5% loss through the drivetrain, and considering my left leg is 2-3% less powerful than my dominant right leg, the accuracy is spot on.
Wahoo provided this graph documenting drivetrain losses of power, explaining a slightly higher reading in the pedals vs the hub.
Takeaways
Initial instillation and calibration are critical to accuracy of power meters.
When in doubt, manual calibrate.
If the data does not seem right, it probably is not. And, there is probably a solution!
PowerTap made one heck of a product in the PowerTap G3 Rear Hub: still providing perfect accuracy after 14 years of use!
Wahoo made one heck of a product in the SPEEDPLAY Power Left Sided delivering the same accuracy of power meters that are far more difficult to install and swap between bikes.