Difference in power from the same trainer

(Paul Ribbons) #1



I have Zwift and Garmin reading from the same trainer a Tacx Neo.
I enclose a brief screen shot of the same ride and as you can see, there are total different readings, any ideas why?

(Steve Ellis) #2
  • Virtual cycling reports 204 W Max Avg Power (20 Min)
  • Indoor cycling reports 248 W Max Avg Power (20 Min)

I’m also curious why those would be different. I’d expect power to be the same. Although it is 20 minute power. Perhaps indoor cycling is not including some period in which you stopped virtual cycling. For instance, if you stopped pedaling for a minute or so and indoor cycling omitted that for some reason (hit pause on the Garmin) but virtual cycling did include it, then indoor cycling could have a 20 minute power in which you were continuously pedaling and virtual cycling could have a 20 minute power in which you produced 0 watts for a minute.

But then again, the durations are nearly identical – 1:31:38 and 1:31:42. The average cadences are nearly identical – 79 rpm and 80 rpm. Those are as expected if both recorded the same event with no interruptions.

The distances and average speeds are quite different, as expected, since one is showing cycling in a virtual world and the other is showing the revolution of a rear wheel on a trainer.

(Paul Ribbons) #3

they were both recorded at the same time off the same trainer One connected via bluetooth Zwift and one Ant+ Garmin, garmin auto pauses, this is not the first time this has happened.


(Steve Ellis) #4

Paul: if you’re so inclined, one way to explore further would be to review both files in third party software. 

  1. get the .fit file off of your Garmin device or from Garmin Connect
  2. download the .fit file from my.zwift.com.
  3. analyze both files in a third party performance tracker like GoldenCheetah (it’s free, open source, robust, and available for PC, Mac and Linux)

GoldenCheetah would let you review the recorded rides in great detail, and quickly tell you what the best 20 minute power was in each file.

  1. Activity > Import from file… (choose file and import)
  2. Activity > Find intervals… (Peak Power > Standard > Find > Add to Activity)
  3. The Peak 20min will be displayed on the Summary screen
  4. The CP screen also shows the critical power for the entire ride, so you can see the best 20 minute power there, or the best power for any other duration
  5. and much more …

(Andre Hufschmid) #5

I bet its settings related. You can set your devices to include or exclude no pedaling phases, that makes a huge difference. I do understand people are looking into power etc but what i don’t understand is why people connect xx devices and compare the readings. Some probably interfering with each other. Stick to one device and it will show your improvement.