Strava shows inaccurate power data

I've noticed issues related to power measuring/output/estimations. 

It appears that for some reason when using a power meter (Garmin Vector/Edge1000) Strava appears to "downgrade" the ride by approximately 15% (both average power and NP), yet when using the Strava iOS app the power ESTIMATE as compared to an actual power meter is about 15-20% MORE than what the power meter is demonstrating. I can see 1-3% differences, but these are huge. I've taken to not relying on Strava for much of anything except for cataloging my rides. 

How in the world can anyone even trust the Strava data? The only thing that appears to be accurate is timing and distance. Even then I've seen minor discrepancies. 

Why is this occurring? Anyone with similar issues? I've got a "ticket" in the queue, but two weeks out and I've yet to hear anything back. 

I've taken to using Garmin Connect since the data is consistent with what the Edge 1000 is reporting. At least I can gauge my performance with some consistency. 

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  • I got same issue. But later on forum some one from Strava tell us ther recalculate data as: Speed, power for a better for us :D 

    They calculating stops and some non sense data. I believe Garmins data on Garmin Connect much more then from Strava. Because Garmin Connect give me data exactly from my devices with take info from my powermeter and rest ANT+ systems on my bike. 

    For example my latest ride https://www.strava.com/activities/563261751 
    Shows me avg speed 30.8Km/h but Garmin shows me 31Km/h 
    both calulate avg speed and avg speed via moving. So different is 0.2 Km/h 

    also power data: Strava shows me 186W NP but Garmin shows me 204W its huge different. 24W its a big different. 

    I dont know why Strava do this. They should take data same as Garmin Connect or TP which use correct Garmin data. 

    Also Strava Correct elevation doesnt work well. Garmin shows me on a different ride climb 720m and Strava shows me only 400m. Really stupid. 300m different??? Seriously???


    I am very sad about this what Strava do with data. 


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  • Did you ever get an answer?  I have the same issue.  My expectation is that Strava would use the actual data.  What did you find?  Thanks, Bill

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  • Bill, never did get an answer from Strava. My general feeling is that they parse the data and then apply their own algorithms to it. What I don't understand is why even do that? The data is there in the raw so why not use that? Frustrated to say the least. 

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  • Same problem here. For example: last ride showed average 238w and Norm as 278w. After loading the ride to Strava it read 238 weighted average power and 168w as average. The difference is huge and I'd love to understand why the big difference.

     

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  • I think its their own algorithm whoes make this problems.
    I think people will much love when Strava starts using raw data and shows them as Garmin Connect. Avg speed, avg speed in moving, climb data after correction same as garmin connect ( they cant use same map system or they use but they got a bug in code for recalculate climb ), power data...i think its not so big deal only if they listen people...

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  • Sucks that you never got a reply for this issue. I have been getting ripped off by sometimes 50w average power most rides. 

    PM is reading correctly, garmin is logging it correctly, something fishy going on when uploaded to Strava though. 
    :( 

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  • Nathan, seems like Strava is mostly concerned about their interpretation of the data rather than just putting it out there. That's the part that we'll never understand because they don't share their thinking behind the algorithms. 

    I've long since moved on from Strava as a means of keeping track of performance. I still use them to log the rides, but beyond that I trust Garmin and others (Zwift, Sufferfest, Trainer Road, Training Peaks) to keep the data true and accurate. Those sites always agree on the data so Strava is the odd man out on this one. Perhaps one day Strava will change their thinking. 

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  • I noticed that issue from the first time I used a Power Meter (which is not the best as it is) however Strava sometimes robbs me for up to 75W. I then synced up Garmin directly to Strava hoping it would go away but the problem persists. The logical explanation I have is Strava don't have agreement with power meter companies and cannot use their data. Even during race one time my Garmin showed a 300W average but Strava downgraded this to 220.

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  • Same issue here.

    On latest ride garmin had ave of 213W. (InPower PM) and strava had 184W

    Could it be PM is discounting zeroes and stops and strava includes them?

    Frustrating

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  • I set my PM to include 0 as I really want to see % of time I produce 0. The interesting thing is TrainingPeaks shows exactly as Garmin does. GoldenCheetah shows what Strava shows. I have cancelled my membership for couple of months maybe they'll fix the bug. I just don't get why can't they take the days from Garmin and display it how it is without doing any further analysis that is basically what public wants !!!

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  • Don't hold your breath on the membership. I put out a ticket on this in April of last year (2016). No resolution. It just appears that Strava has their own set of algorithms that they and only they understand. As you noted, Training Peaks demonstrates the Garmin data. So does Trainer Road. I use Strava primarily as a catalog to keep track of rides. It's also in Garmin Connect so I'm pretty much covered. Maybe we'll know someday why these rides are so different from platform to platform. 

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  • I've started having the exact same issue since switching from a 4iiii Precision to a Rotor InPower and that is very frustrating. Have you guys been able to find a solution after all this time?

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  • Xavier I haven't been riding much due to some issue s with a right knee however what I did I put all setting on garminConnect and computer to include 0 settings. They were included before but I checked to make sure. I am yet to try it.

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  • same!

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  • Strava, why cant you just allow power data from a power meter to be recorded? Why do you have to manipulate it? 

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  • So what is going on with this then?

    Strava, we are paying members. Why haven't you addressed this issue and why haven't you addressed this thread?

    It is on your support site!

    Please can you respond. You offer a great service but there is obviously something fundamentally wrong here.

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  • Thanks everyone, 

    Strava does include zeros in average power, but normalized power should be a better representation of your power output without the zeros. However, I do suspect that setting your Garmin to exclude zeros causes the discrepancy here. 

    I'd be interested to have a few of you confirm this setting on your Garmin before we move forward with the discussion? 

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  • Elle Anderson;

    You are correct in a sense that Strava shows normalized power vs average. I have turned 0 setting off but discrepancy still there. STRAVA should and must take the data from 3rd party sources( if used) DIRECTLY w/out applying their comprehensive algorithm and must only do so if the sources not present. Faster response is appreciated.

    Regards
    Alex

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  • Thanks Alex, can you clarify what you mean with turned 0 setting off? Do you mean you have turned off the setting to exclude zeros on your Garmin? 

    If you'd like to share the activity with me I'll be happy to look into it further. 

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  • Elle,

    Yes I have turned off the setting to exclude zeros. I stopped premium membership untill this issue is resolved. The point is not about what my activity is the point is that STRAVA must link third party devices and upload directly and only use their algorithm if those sources are not available. Thanks for response.

    Regards
    Alex

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  • I also have zeros included for average power calculations on my Garmin. Every other software available be it from Garmin or third party shows the right data so I have a hard time seeing how this isn't a problem with Strava itself which is quite frustrating.

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  • I took an example activity from Alex BK: https://www.strava.com/activities/1100055569

    (Hope you don't mind Alex!)

    Strava lists the average power as 166w. 

    TrainingPeaks and Garmin Connect list the average power as 210w. 

    Interestingly, Alex reports above that he HAS turned off the setting that excludes zeros, so that means that zeros should be included. 

     

    When we analyzed the power data from the file, there were indeed zeros present (this just confirms that the Garmin device is recording zeros in the data stream). Zero power should be recorded when you are not pedaling but still moving. I don't think zero power will be recorded when you are stopped...but this could be interesting to dig into to confirm that Garmin isn't recording zeros when you are stationary.

    In the above example, Strava is including the zeros to get an average of 166w.

    After a quick calculation, it seems that if the zeros in the above file where excluded, the average power would be about 210. 

    This appears to indicate that Garmin is recording zeros, but still excluding them from the average watt calculation. It could be worth experimenting with Golden Cheetah which is a data analysis software that allows you to switch between the two according to this discussion.

    Happy to look into other examples, so just let us know. 

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  • Elle Anderson. I dont mind at all. If you want to truly compare data I can send you numerous Garmin files from this week and you can compare it to STRAVA.

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  • That example looks like a coincidence to me. I've just completed a ride that was purposely unbalanced (ie: lots of coasting and lots of sharp efforts): https://www.strava.com/activities/1105868824/overview

    Strava gives me a 135 W average whereas Garmin Connect gives me 144 W so still a similar relative difference as my other rides (ex: my july 8th ride is listed as 186 W average on Strava vs 192 W on Garmin Connect).

    Thing is, both these rides are completely different when it comes to the amount of time spent at 0-25 W according to the Strava 25 W distribution. The first one has about 45% of the ride spent there whereas the second one has about 15% spent there. Now, the relative difference is roughly 6,25% and 3,25% so not much of a correlation with the amount of zeros there (less than 2 times as much vs 3 times as much). Also, you'd expect 45% of zeros to mess up the data much more than a mere 6%.

    Another thing to consider is that with the exact same Garmin settings, my other powermeter (a single sided 4iiii Precision, the issues being with my single sided Rotor InPower) gives exactly the same data on Garmin Connect and Strava.

    As previously asked, it all comes down to a very simple question: Why does Strava need to recalculate the averages for some reason even though Garmin already does it and does a better job?

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  • This is no coincidence. My average power does indeed show 210 W from Garmin. And my zero setting is off. I am not sure what Elle is saying here. My normalized power close to 235W. If Strava uses "weighted average" then the terminology should match and even still there is a discrepancy. The point is that why STRAVA doesn't take data from Garmin directly.

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  • Another note, Strava does detect outliers in the power data (a sudden jump to 1000 watts for example) and removes these erroneous values. So, it is possible that if Strava detects and removes these outliers, and Garmin does not, you may see a difference in the average values, zeros aside. 

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  • Elle,

    These sudden jumps are important values. These values show instantaneous power that is critical for analysis

    Alex

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  • Also, here is some additional info regarding weighted average power: 

    Weighted Average Power is similar to - but NOT the same as - Garmin's Normalized Power.
    Both numbers attempt to capture the average effort of a workout by taking into account lactate accumulation and other types of fatigue. Strava uses an algorithm very similar to xPower for computing Weighted Average Power.

    There will be differences between the Weighted Average Power and Normalize Power. How much and which direction will depend on the ride. Typically, for shorter rides, Weighted Average Power will be lower than Normalized Power. This is a result of the different types of smoothing used by the algorithms. Both numbers have been used successfully by professional coaches.

     

     

    As to the question of why Strava can't simply copy values exactly from the Garmin file in regard to average power and normalized power: Well, our engineers have worked hard to process the raw data in the file, clean it up, and use algorithms that are standard across any file created by any compatible Strava device. It's just the way we have always approached activity data. We don't have plans to change or disable these core functions and algorithms in our data processing. 

    Please let me know if there are any other questions. 

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  • Hi Elle,

    How are we supposed to record data, analyse it on Strava, and use it to better our training and cycling when there are such large discrepancies?

    The values shown on Strava contradict the live data we are are viewing during the activity! 

    How is it possible then for Strava be used as a viable training platform?

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  • Hi Jack, might be helpful to look at an example of where you feel the live data you see while recording is not reflected on Strava. Thanks. 

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