Hello. I am quite new using Zwift. I have used my HT Elite Turbo Roteo Smart b+ for about 2 weeks now with my Garmin GPS. And it worked just fine. Speed, Power and cadence seem accurate and the effort pretty much the same as when I’m riding outside. However, the speed shown in Zwift looks completely inaccurate.
most of the time it’s way above my average speed.
Is there any way to calibrate this ? I have to admit that I’m pretty lost on the app. I tried using on Android, and on my Windows Computer, but cannot find settings.
Here is an example of what my Garmin tracks compared to a Zwift render :
Thanks in advance for your help.
The Garmin (bike-computer ?) is wrong. Change the settings (wheelsize) there.
I really should make this a sticky:
Zwift takes the wheel speed broadcast by your speed sensor and the power curve of the trainer you select on the Pairing Screen and converts that to virtual watts. With those watts, the weight entered, height entered, in-game bike used, in-game drafting (Tri and TT bikes get no drafting boost), in-game wheel set, in-game road surface, and in-game virtual elevation changes your in-game speed is determined.
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Thank you for your reply.
Does this mean there is a way to correct it? Because I am not riding with a speed of 29,7 km/h on average, and the distance at the end of the ride is wrong.
I’d like to have a more realistic total at the end of a ride so that it fits to my actual effort.
Edit: the watts and the cadence are both similar in game and on my Garmin edge (which is normal because the sensors are broadcasting the same metrics)
Please reread my post, the speed and distance that Zwift shows will hardly ever match what your bike computer shows. It does not mean either is incorrect.
Sometimes it takes new users with speed sensors a little while to grasp the concept.
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Thanks for your answer. Well I have followed my home trainer instructions. I have a wheel circonference of 2100mm.
the instructions say that on Garmin you have to put 2100/25.34= 82, 87 ~ 83.
And the results on my Garmin edge are almost as accurate as when it uses the GPS data outside.
I think the informations shown on Zwift are way too high comp red to what I am used to provide while riding. The distance and the speed seem over estimated.
Again, Zwift has variables that your bike computer does not know about.
Ignore what the bike computer is reporting about speed and distance.
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I have read several times, please believe me 
I am new here, and I understand that different inputs are taken into account to give the speed metrics. I am more giving credits to watts and cadence in order to know what I am doing.
But it seems weird that the total distance and speed are so different from an “ordinary” ride.
Within Zwift there is no wind, no cars, no stop signs and no slowing for corners.
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