Speed Sensor issue

I have a Basic Turbo Trainer, that i use my Garmin Edge 500.

This is my first time using Zwift but i have notice that on my Garmin my Speed was showing 35km per hour, but yet on Zwift i was only doing 17km per hour.

I had to work harder to hit 30km per hour on Zwift…

What’s the question? Is it ‘why is the speed lower?’

My understanding is that Zwift works out your power (if you don’t have a power meter). It then divides by your weight to get w/kg. Your speed in the game is then purely based on w/kg.

I ride rollers, and on a hill, I can be doing 45k/hr on the rollers and only 10k/hr in zwift.

Hi David - 

The reason you are seeing different numbers between Zwift and your Garmin is because your Garmin is displaying the speed you would be generating on a flat road without any other variables. In Zwift, your speed is not only determined by your power, but also the weight of you and your kit, the gradient of the course, and other similar factors.

You may have to work very hard to hit 30 km per hour on the flat, but will have to work much harder to hold it on a climb, and not nearly as hard on the downhills. 

I hope this helped explain!