I’ve figured out what is causing my SB20 to overreport power. I have varus knees and a wide pedaling stance. The Stages cranks (gen3 hardware) seem to be including lateral (off-axis) force vectors when it should only be accounting for axial forces in its power calculations. When I pedal with an exaggerated stance as if I’m pushing my knees+lower legs outward, my the SB20 inflates my power relative to either my Vector/Rally pedals or my Assioma pedals. When I pedal with an exaggerated inward pushing motion as if I’m trying to crush a watermelon between my lower legs, the SB20 reports lower relative power vs the pedals.
If anyone else has both an SB20 and power pedals, I would be grateful if you could perform a similar test, recording two FIT files for direct comparison.