I use roll Trainer Tacx Bushido & Zwift & Garmin Edge 820 on my bike.
So, when I ride a workout, I have different data on Zwift and Garmin Edge 820. Yesterday I ride a 1h workout, Zwift recorded 13,8km, 401hm, and the average power was 161W. Garmin recorded 16,8km, of course no height meters, and a average power of only 46W.
Also I see, that the speed in the mountains (with 5-6% grade), is very low (~ 3-4km/h).
In the flat it seems that the differences are not so big. After start Zwift and Garmin recorded nearly the same, but when I come into the mountains, it differs a lot.
I putted in height and Kilogramm of my Person in Zwift, also the max. heart beat rate.
So, I don’t know how arise this different data. Also I don’t know, what is right?!