HI,
I bought the garmin rally rs200 a few weeks ago and I noticed that after 45'/1h of pedaling the power is underestimated by 20/30 watts and also the right/left balance is 61/49% LR. How can I solve the problem?
in this segment of strava it can be seen that with 4 watts less of average power I lowered the old time by almost a minute, I would like to point out that the weight of the cyclist and the bike has remained the same, similar climatic conditions with no wind.
so, what i found: here is the suito - rs200 graph, i think here the problem is that the Suito was not spindown calibrated after a 10mins warmup (when it is warm enough) but just cold . is it true? (usually the best method to do a spindown regularly after a workout but not when it is cold) Your balance was L51-R49 /L50-R50 at the beginning and after it went to the L48-R52 range. in ideal condition the difference between the trainer and the bike power meter (if that is dual/total powermeter) is between 1-2-2.5% maximum, (small ring front, middle at rear), if you are training on big ring (which is a mistake on indoor trainer in ERG) and lower gears (near to 53-11 , -12, -13), then the difference is bigger , but never 8-9% , at least i never experienced such a big drivetrain loss :)
lets see the outdoor ride, that is much more interest . before when You started that 15mins interval on the hill, your balance was aprpx L57-R43 (which is really weird and bad data i think), and as You started the climb, it started to change heavily (and i think it caused the power drop too, here is the graph) and went down to L42-R58 which is abnormal behaviour. i dont know what happened here (loosened pedal/s/ maybe after a dis and remount, it needs 40NM torque , otherwise if the pedal is rotating a tiny bit then the presetted angle will be different as the real axle angle is, at least it was the situation with the older Garmin pedals in the past, as i know it has already an automatic angle verifier algorhytm but this auto things could be wrong sometimes as the auto-zero too with this Garmin pedal-family, never trust in that) the temp was almost stable 13-15-13C, so it cant be temp drift in the pedals. what i suggest to do when you install the pedals: always torquen the pedals with 40NM, do a few short but intense sprint, then angle setup and manual zero calibration. and after these everytime when you train, do a manual zero calibration on Rally, i know , there is an auto-zero (within a narrow range, so it is not 100% trustfully) in it but the best is the manual zeroing and avoid the auto things 
