I have a calibration issue with the Wahoo Bolt when paired with the Wahoo Speed Sensor that I can't seem to solve.

When the Bolt is computing speed and distance from the speed sensor, the results are consisently 5% optimistic compared to Strava on my iPhone. However, if I unpair the Wahoo speed sensor and allow the Bolt to pull data from its own GPS sensor, the results closely match Strava.

So Wahoo techinical support suggested that I take precise measurements of my wheel circumference (the speed sensor is attached to the hub and only knows revoluations) and calibrate based on those results. It turns out that my wheel is 2133.6mm round and the calibration I had already set the Bolt to was 2136mm. This is a difference of <0.2%, well below the 5% difference I'm measuring on the road.

I want correct speed and distance readouts, but my two methods for checking calibration errors differ. Does anyone know what might be going on here?

Thank you,
Robert