Ant+ Sensors and Power Meter Pedals/Trainer

I have a few question on sensors and power meters (pedals and trainer). I have the following setup. 

Power Meter Pedals: Garmin Vector

Smart Trainer: Tacx Vortex

Speed/Cadence: Combo Sensor


  • Why do my cadence readings vary depending on the sensor? Before I begin my ride I have the option to select any of the above for cadence. When I select the pedals or trainer both readings are almost identical if not the same however if I select the combo speed/cadence sensor it varies quite a bit. Pedals/Trainer ~80 vs Combo sensor ~105+. The measurement however only varies on Zwift. If I record my activity on my Edge and Fenix I get the same cadence reading on both devices. 
  • Power Meter variances? I know there’s some smoothing being done on Zwift however I’m not entirely sure how much. I haven’t had my pedals very long, and just bought my trainer, so I’m still learning about power. I calibrate both the trainer and pedals before each ride but readings vary quite a bit. I should note, I use the trainer with Zwift as well as record my workout on the Edge using the Vector pedals. Any ideas or suggestions as to what I should do or focus on? ie. Zwift or Edge recordings?
  • Given that the “Smart Trainer” broadcasts all important variables (Power, Cadence, and controlled by Zwift) should I simply set the software to use it for each setting?


Thanks in advance. 

Regarding the Power Meter pedals question and ‘what to focus on’. I’ve got Vector pedals that I use on both on the road and with Zwift. And I own an Edge 520 (plus an older Edge 800). On the Edge devices I run the display to show ‘3sec average power’. While at any instant power readings between these devices will vary, in my experience it really doesn’t matter which you look at. 

When I am on the road I typically have both the 520 and the 800 and I like having both devices when I am using the realtime map on the 800 (and can still see all my data on on the 520 at the same time). Similarly when I am looking at realtime Strava segment status, I can see all my data on the 800. But often I have the same data showing on both devices, the power readings (at any instant) may not be the same, and I don’t think it matters as they quickly converge (or cross). I tend to focus on the Zwift readings indoors and use the 520 simply because it provides a simpler path to Golden Cheetah (by a little bit). And I know what Normalized Power is and have only a vague idea what Effective Power in Zwift is.