Tip when comparing Stages vs Kickr Core power meters

I wanted to see how much difference there will be in power output when switching from using the Kickr Core power meter to my new Stages L crank meter. I setup dual recording sending the Kickr Core power meter to Zwift and the Stages power meter to the Wahoo Bolt.

What I learned: While the Bolt displays a 3 sec W average on the head unit, the .fit file it produces shows the raw instant power data. When Zwift is set to a 3 sec W average the .fit file it produces shows the smoothed 3 sec avg data.
So, to make an apples-to-apples comparison you need to set Zwift to instant power readings.

Conclusion: With a completely clean drivetrain, over a one hour workout, here are big gaps in the Zwift Power graphs when ramping up and down and there’s a nearly 9% difference in max Watts BUT the average power for the whole ride differed by less than 1%.

That’s a smaller difference than I was expecting. My first thought was relief that my numbers shouldn’t change much after the switch. But now I’m almost worried that seems too close, like maybe one of the meters is off? Anyone else tried this?

As a “car guy” (ie. former automotive mechanical engineering background) I can tell you that differences in power levels between the crank(shaft) and the drive wheel are not only normal, they are to be expected. If they didn’t exist, you’d suspect something was wrong.

Big picture: power losses between crank and drive wheel on a bike are pretty minimal, at least compared to a car. But they still exist, and there is obviously going to be a bit of a lag as changes in torque and RPM move through the drivetrain.

Don’t expect any power measurement system to be perfect. None of them are. But you can do a heck of a lot with the data they provide all the same.

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