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Edge 520/Garmin Connect and Strava shows different values for average power

This has been a problem for the last couple of weeks.

Before, average power used to be the same in garmin connect and strava.

Did a testride today, and seems that laps where i pedal all the time gets pretty much the same avg. power (Lap 2 and 6).

Garmin is set to include zerovalues.

Exported the ride to .tcx and did calculated the avg. power in lap 7 manually, got these results:
With zerovalues: 56W
Without zerovalues: 138W

Garmin Connect/Strava shows 68W/52W for the same lap.

What is wrong?

I have attached a photo of the values from Connect/Strava and the .fit-file form todays testride

0 aweatherall over 8 years ago

The public FITSDK does not decode the RX rates. I have access to some tools because of prior work I have done that is covered under an NDA that allows me to see the values. I believe that the FITFileReapirTool has reversed engineered this information.

Anything below around 90% can start to cause noticeable issues with power data.

The ride that I looked at 2016-09-11-14-25-20 was below 60%.
Ride 2016-09-11-18-31-36 is better as it is in the low 70%, but still not great.

0 aweatherall over 8 years ago

I cannot view your Strava activities to see what is happening at the lap level. I don't know if they are private or only accessible to your followers.

One possibility reason why things might be different when climbing hills is due to cadence.

The Stages power meter is an event based power meter. It changes the message content on each completed crank revolution. It is transmitting at 4 Hz so if you were riding at 60 rpm then each message would get repeated 4 times before it got updated. If you were riding at 120 rpm then each message would get repeated twice before it was updated. If there were short breaks in the communication you can see that the lower the cadence is the greater the chance of the Edge being able to pick up one of the messages that has the a repeated value.

The above description is a simplification as other message are also sent periodically that will take up one of the 4 Hz slots.

0 DanielBrodshaug over 8 years ago

Ok, they where private, but should be open now if you would like to see.

Testrides from yesterday:
https://www.strava.com/activities/708248727
https://www.strava.com/activities/708248768
https://www.strava.com/activities/708359636
https://www.strava.com/activities/708719701

Testride 3 includes the short uphill lap where avgP matches perfect. Testride 4 is when I changed garmin mount, so RX went from <60% to >70%.

Could you check the RX for this ride from july 15th? Trying to troubleshoot which cockpitchanges affects the RX. Will try to remove the aerobars tonight.
https://www.strava.com/activities/641638836

0 DanielBrodshaug over 8 years ago

896

Ok, they where private, but should be open now if you would like to see.

Testrides from yesterday:
https://www.strava.com/activities/708248727
https://www.strava.com/activities/708248768
https://www.strava.com/activities/708359636
https://www.strava.com/activities/708719701

Testride 3 includes the short uphill lap where avgP matches perfect. Testride 4 is when I changed garmin mount, so RX went from <60% to >70%.

Could you check the RX for this ride from july 15th? Trying to troubleshoot which cockpitchanges affects the RX. Will try to remove the aerobars tonight.
https://www.strava.com/activities/641638836

0 DanielBrodshaug over 8 years ago

Dont know what happend to my last post, here is yesterdays rides:
https://www.strava.com/activities/708248727

0 DanielBrodshaug over 8 years ago

https://www.strava.com/activities/708248768

0 DanielBrodshaug over 8 years ago

https://www.strava.com/activities/708359636

0 DanielBrodshaug over 8 years ago

https://www.strava.com/activities/708719701

0 DanielBrodshaug over 8 years ago

Now the strava links should be open, activities was set to private yesterday.

Ride #3 has the short uphill lap that matches perfect with Strava.
Ride #4 is where RX went from <60% to >70% after changing garmin mount.

Could you check RX for this ride under? Trying to troubleshoot which cockpitchanges that affects RX.
https://www.strava.com/activities/641638836