Pete’s advice applies to all trainers ever produced as opposed to killing several hours giving specific information by make, model and year. Rules of thumb are just that, broadly applicable.
For me my trainer returns the same value every time I calibrate it. For 6 months I used my PM and my trainer and constantly compared values between the two. After I figured out my trainer does not need to be recalibrated, I stopped recalibrating it. But that’s me and I understand my equipment. So the rule of thumb for me is not that helpful but to someone that doesn’t care to invest the time or has invested the time and sees their trainer requires more calibration, calibrate more often
I have a Wahoo Kickr Snap and I use PowerMatch with a Stages power meter. I calibrate my power meter before every ride, but I haven’t calibrated my Wahoo Kickr Snap in at least two years. No issues at all.
On my Power2Max, I only need to stop pedaling for three seconds for it to automatically zero offset, with no effort on my side. I try to remember to do that ten minutes or so into an outdoor ride, but even if I forget, it’s rare I have an outside ride where I don’t stop pedaling for three seconds.
When I use my Kickr, I always start a workout from the very beginning, so if I would do a spindown every time, I’d have to interrupt and pause the workout, go through the app to do it, and it takes 30-60 seconds. That’s a bit more of a buzzkill than the P2M’s 3 seconds of no pedaling.
I typically do a spindown once or twice a month when I’m done with a workout. I rarely move the trainer, and it’s set up in a basement that’s very consistent in temperature, so I’d be surprised if the power reading fluctuates much on it between spindowns.
