Garmin connect shows a max power value not seen in the fit file sensor data

Hey all, I’ve been looking at files forever and ever and this is a new one to me.

Buddy of mine got a new power max today according to his head unit, and also on garmin connect. 1100 something.

Strava shows 900 something, so I asked him to send me the .fit file.

I looked at sensor data, and the 900 something is all that I am seeing in the .fit file sensor data, but Garmin Connect shows 1100 something. He sent me a screenshot of his GC page. And it displayed it on the head unit.

Anyone ever seen a disparity like this? I haven’t. I would like to maybe get to the bottom of why GC says one thing, .fit file as viewed by WKO5 says another.

Thanks
PHOTO-2024-04-10-17-34-40


I just got a power meter for my XC bike and used it for the first time yesterday. I’ve never had power outdoors, only ever had it on my trainer. Its a 4iiii left side XTR crank pm. For yesterday’s ride strava is showing 960 max, Garmin Connect is showing 1062.

Have you had a look at the file using FIT File Explorer? (Mac only iirc)

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Good idea. Here’s what FitFileExplorer shows. 1150.

Question - is that in the summary message (FitFileViewer) or in an individual data message? Maybe one-off bug when the summary was written.

Interesting

This guy is also using a 4iii powermeter non drive side powermeter.

A Shimano Ultegra R8100 with 4iiiis Power Meter.

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Good question

Summary.

When I examined the individual data records, this is the max value that I was able to find. No 4-digit power number exists.

ok maybe this is useful from garmin forum member aweatherall which is like hearing from moses. Yes I realize this is talking about average power and not a single data point.

Average power discrepancy between Garmin Connect and Strava - Edge 1040 Series - Cycling - Garmin Forums

Here’s the text of his reply

So the difference is due to the fact that the Edge and Strava are computing the value off of different values in the FIT file.

The discrepancy between the values if due to communication issues from the power meter to the Edge and how those lost signals are managed.

The power meter sends torque/cadence from which the Edge can compute power. Each message also contains an accumulated value.

If you look in the FIT file you will find an accumulated_power value and a power value. If there were no data loss then the sum of the individual power records would equal the reported accumulated power.

In this case there is around a 5% difference.

The accumulated power is 1564778 kJ

The sum of the individual power records is 1486061 kJ

The activity duration is 8,688 seconds.

This gives averages of 180 and 171.

if you look at the plot below you can see how these two values diverge.

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Summary message it is! And yes, he is the almighty on Garmin forums LOL

Are all the data records a second apart or are there gaps where smart recording has trimmed some?

second by second there is a record

yes, thats different.

Open the file in FitFileViewer.com and then open the Session message and scroll until you see Max power:

image

What do you see?

Same as in the fitfileviewer application. 1150. But there is no 1150 in the second to send list of records.

Apparently the bike computer made an error when computing the Summary, and then:

  • Garmin Connect appears to be showing the incorrect value from the Summary
  • WKO, Strava, and others are finding a max from all of the 1-sec power records

The power meter talks to Garmin more than once a second. Therefore possibility your Edge saw the 1150W value but it didn’t make it into the lower resolution second by second fit file.