Speed and power doesn't match.

I have in my bike a Garmin speed sensor and power tap chain ring from CycleOps, and I have my bike connected to my ClycleOps PowerSync bike trainer. When I ride with Zwift the speed never match with my Garmin computer and I can see on my Zwift screen my speed going up and down when I keep the same gear and cadence where at the same time my Garmin still have a steady speed.
That frustrate me a lot. Is anyone can tell me why?
When I link Zwift with my trainer should I use my bike trainer to give me the power or my bike power tap?

Ignore your bike computer, the speeds will hardly ever match.

Speed within Zwift is determined by your watts, ingame weight, drafting, ingame bike used and elevation changes, your bike computer doesn’t know about this.

Your choice on what you choose for power, but I would pick the PowerTap since it’s comparable to outside rides and more accurate power readings.

 

Hi Marcelo

Don’t think I understand what you are saying, is it …

When you are riding indoors with the same cadence and gear you are in effect riding a flat course, Garmin will read a steady speed, as it should.

But, on Zwift, the course has hills. You go up a hill on Zwift with the same cadence and gear, you will slow down, unless you apply more power or change gear.