Garmin speed is slower after I connect to swift

If I ride at say 170w and my Garmin speed is 28km/h. What does it drop to 20km/h if I connect zwift ?

Wattage is the same on both Garmin and Zwift.

Hi Adrian—What trainer set are you using?

Wahoo kickr 2018.

Please read this: How Does Zwift Determine My Speed?


The challenge i have is that my Garmin speed changes for the same wattage after I connect to zwift. I understand that Garmin and Zwift will not show the same data.

Can you help with that please?

Just ignore the Garmin speed, you are over complicating things by having it.

On your Garmin just track HR, power and time, speed does not matters since in reality you are not moving at all.