I have been struggling to try to understand the power differences I get between my Stages L/R power cranks and my 2017 Wahoo Kickr (see Power mismatch -- Wahoo Kickr vs Stages Cranks). In a nutshell, I am seeing a greater than 10% difference (with Kickr being higher) between the two power levels when doing TrainerRoad intervals in ERG mode. When just riding on Zwift in SIM mode, the power levels seem to be much closer together.
Well, I had been doing all my TrainerRoad workouts in the big ring (53-14 or -15). So, after reading through this thread, I decided to do today’s workout (Antelope) in the small ring (39-17 or -19). Well, in the small ring, the Kickr and Stages power levels were very close to the same! I did the last interval in the big ring, and the big difference in power levels (with Kickr being higher) returned.
Subjectively in that last interval where the Kickr power level was higher, I felt like I was actually putting out that power level. But there were also times when I felt like there was a bit of almost “coasting” going on when I overshot the target power and the Kickr was adjusting.
I haven’t done an FTP test in the small ring, but I have done the tests with Kickr power versus Stages power in the big ring. With the Kickr I was at 237; with the Stages, I could only manage 202 (though I was not in as good a shape, but should not have been that different!).