Okay, so we agree that the drivetrain power loss is somewhere in the 3-4% range and probably much closer to 4% with a typical road 2x gearing setup. So power measured at the pedals should be 3-4% higher than power measured by the trainer at the rear hub.
You say the Assiomas are listed as +/- 1% accurate when calibrated and the Kickr is +/- 2%. So unless at least 1 of these devices is incorrectly calibrated, or faulty, then I don’t see how it is possible to end up with power measured apparently 2% higher at the trainer. That would require at least one of these devices to be well out of its stated spec. If the Assiomas were reading -1% and the Kickr was reading +2%, then you would still see a 0-1% higher power reading at the pedals.
FWIW in my setup with a crank power meter and Elite Direto X (which has an optical power meter) I consistently see 4-5% higher power measured at the crank, which is exactly what I would expect, knowing that my drivetrain is not perfectly clean!
Has it continued to consistently be out by same % even after spin downs etc.
Have you been using assioma Uno or Duo. Guess if your left leg was weaker the assioma uno’s would under read. Eg if left/right split was 45/55 (quite extreme but not impossible) the assioma uno would register 90% (2x45) of the actual power you put through both pedals together.
2% lower would fall within the combined range of stated accuracy of the two devices though, so it’s not the biggest problem in the world and if they track, then they’re both consistent, which is enough to work with when training.
That said, I have both a Core and Duos and find mine to be pretty much 1:1 if both calibrated.
Just to revisit the first point though, the Assioma Duo give a stated accuracy of +/- 1% and the Core +/- 2% which could combine for a 3% discrepancy in the worst case. Your 2%, so long as they consistently track, is basically “good enough”
I switched the Assioma Duos back onto my outdoor bike so haven’t compared them in a while. I think though the answer to my question is that it falls within the accuracy range for both the Assioma and Core. My left/right split is normally 49/51 so too close for that to be the issue I’d say
I have a substantial difference in watts of around 20-25, between what the Kickr Core calculates and the Assioma Uno pedals, both with calibration performed.
I view the Assioma uno on Garmin 1030 while the Kick Core on the phone app or on the tablet with Zwift. Can someone help me to fix this difference?