mph not the same

Just done 10 miles on zwift island and saved to strava,this gave me an average mph of 14.2. I also recorded the ride on my Garmin 800 which I also loaded to strava this gave me 15.7 mph!!! slight difference
Steve

The speed calculated by your Garmin does not take into account all the virtual factors of Zwift Island - they will never match up.

Ok thanks Eric