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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  • Cool,

    Here is a link to Strava from a ride I did today with zeros not included and auto pause at 6.4kmh:

    https://www.strava.com/activities/1115202108

    Here it is on Connect:

    https://connect.garmin.com/modern/activity/1893449704

    Here is pretty much the same route with zeros included:

    https://www.strava.com/activities/1066722914

    and on Connect:

    https://connect.garmin.com/modern/activity/1834244881

    Jack

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  • Hi Elle,

    Just wondering if you've had a chance to look at these activities?

    So does Strava apply algorithms to ‘smooth’ out values like speed, distance, power etc. as gps might drop out on the Garmin? Is this because Strava is accessible on a number of different devices and you want to insure a consistency in data across the board?

    Surely power is absolute like cadence and heart rate which I see no differences in between the Garmin and Strava.

    Even if it is not and there are some discrepancies and system errors in the source file, they are few and far between. It is still happening on the device and is the data that we are seeing during the activity, which is what matters.

    How are we expected to correlate the live data we see during the activity with the data we see in analysis on Strava if it is getting smoothed out via you algorithms?

    In other words, how are we able to use Strava alongside a power meter?

    I don’t get it.

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  • Let it be said that Strava parses the data from any device to their liking. Plain and simple. But the issue is huge. Let me explain. Most of us who are on Strava do so because we want to keep track of our rides and see our progression over time. We also want to be able to correlate what we see on the road LIVE in comparison to Garmin Connect, Training Peaks, Trainer Road, Zwift etc., data. Why? Because of the sweat and effort that is put into these rides. AND... we want to know that what we see on the road is reflected in our training, both indoors and out. Hence, if Strava downgrades the rides (especially Power) then it's really hard to know what is "real". Is our power meter lying to us while we are out on the road? Doubtful because I also train on a Wahoo KICKR and it reflects much of what I see on the road. Are we in reality, not progressing like we think we are? Hence, the frustration from so many of us on this forum. 

    Ironically, I did several rides using the iPhone Strava app alongside my Power Meter and Garmin Edge 1000.  Guess what? The Strava app overestimated the power on the ride upwards of 20%. I've also ridden the same ride with friends who only used the phone app. Guess again - yup, they produced lots more power than I did, yet we began, rode and finished the ride together. Makes no sense. And yes, I'm taking into account weight of rider and bike and in fact am using watts/kg as my baseline measurement. Not just pure wattage. 

    I for one have long since stopped using Strava as a training aid. Like I've mentioned in the past, it is only a catalog of rides and nothing more. When my Premium membership comes up for renewal I'll be cancelling it until Strava decides to take the raw data and quit manipulating it. I started this thread over a year ago and Strava stubbornly refuses to budge on their algorithms and massaging of data. Why?

    Elle has not offered anything more than "let me see your ride". Geez! You've got thousands on your site! They have the raw data. Don't just give lip service - look at the damn data! 

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  • Hi Jake, 

    That is correct. Strava looks for outliers in the streams that are imported in the file: distance, power, heart rate, elevation, etc. For example if power data spikes to 1000w for just one second, that value would be removed, and averages recalculated. Similarly, if a large acceleration in speed is detected between points then Strava removes that point and recalculates the distance using the remaining coordinates. 

    Strava does this for all data imported to Strava, regardless of device. 

    You are also correct that these types of errors shouldn't happen often. Garmin usually does a good job recording data accurately. I don't think this outlier detection is the cause of the discrepancies reported here. 

     

    What Garmin does to calculate stats and averages on the device itself is not known. When Garmin creates the file, there is the raw data for each data point but there is also summary data at either the beginning or end of the file. The Garmin device computes a single value for average power when it creates the activity file, before uploading to any platform. For power, for example, there is a single value for average power under the Extensions field. For your ride on August 3rd it appears to be 269w. For your ride on July 4th, it appears to be 189w. Without contacting Garmin, I have no information about how this number is computed. 

    Here's what I did to troubleshoot: 

    1. I downloaded your original Garmin files and uploaded them to a Garmin Connect test account. The average power shows 269w and 189w respectively.

    2. I then exported the TCX file from Garmin Connect and opened it in a text editor. At the end of the file under Extensions I found the average power field and I removed it.

    3. Then I re-uploaded the TCX to Garmin Connect with the average power field removed. Without being able to rely on the Extension field for average watts, Garmin Connect must re-calculated the average power data based on the actual raw data points recorded in the file. The result? 142w and 131w respectively for average power. 

    4. I uploaded both files to Strava next. I got 168w and 148w respectively. 

    Where does this land us? I can't tell you how Garmin computes average power on the device. But I can tell you that once that value is removed from the file, the average power computed by Garmin Connect using the raw data is different and much lower. There is not one definitive answer regarding average power. It's possible that moving time or auto-pause is also impacting these averages (I notice the TCX version on Garmin Connect computes longer moving time for both files: 1:11:28/1:16:02 and 1:16:37/1:25:42 respectively). 

    The above is all the information I can provide at this time. 

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  • Elle,

    This is absolute nonsense. Garmin takes raw data and shows it in graphical representation against time speed elevation etc. So does TrainingPeaks GoldenCheetah (difficult to use btw) and many others. Only Strava throws away instantaneous power points. What if the rider wants and capable of pushing 1000W for 10 seconds does that mean this result will be filtered out. What you have described it sounds as STRAVA makes it's calculation as a Bell curve meaning collects data points and then concentrating on average while filtering extreme right and extreme left points. (Worked on Radio Development for many years so I can do a little questioning about those things :). )

    Regards
    Alex

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  • Alex, 1000w for 10 seconds would not be filtered out. The threshold for what is considered an outlier is pretty strict. This is not the most common reason power numbers don't align between platforms. 

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  • Ellie, the people who invented Power as a cycling measure (Training Peaks - Joe Friel, Hunter Allen) are consistent with Garmin. So Strava knows better? I don't think so. In the end, Strava will lose its most valuable passionate members...those who scrap for every watt. Until you come to that realization, you will be trying to win an unwinnable debate. I have a Training Peaks membership and WKO4 and subscribed to Strava to support you guys. No more. Strava just lost my Premium membership as of the end of the month.

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  • Same issue here - using Garmin Vector pedals, my Edge 810 during today's ride, matched what Garmin Connect shows: an average power of 205W.

    Yet on Strava, which claims it is taking the "data from a power meter", it shows 185W average power: 10% out.

    This seems to happen on each ride - only that today was the first time i've decided to Google it to see if it is an issue that other people are having. If the data is just synced from Garmin Connect through to Strava, how is it being adjusted/recalculated in a way that doesn't match the source data? (Zeroes ARE included in my Garmin data)

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  • Bill ,

    Spot on. Those guys directly analyze raw Garmin data and the fact that STRAVA doesn't makes me aggrevated on top of it all on my cell phone i see one number and on computer another. I don't know what's what anymore so I stopped premium membership as well back in June. It causes nothing but confusion and inaccurate data analysis. FYI Elle there is a thing known as instantaneous power which is critical to some users; so when STRAVA filters it as you said it does then what good is STRAVA

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  • Have to agree that this is like getting blood from a stone. I will continue to use Strava because of the StravistiX extension I can add to chrome, which matches the data from my power meter fairly accurately (much better than Strava which is usually about 15%-20% lower.) Otherwise, it's useless as a training tool, but after all of the comments I have seen here (and on other forurms,) I do believe that Strava is focusing it's efforts on the social aspect since others are doing the analysis bit so much better. 

    Strava also cuts mileage and adjusts MPH, for some reason. How hard is it to give me a representation of my ride? How about giving me the option to take power directly from my power meter instead of sending it through your algorithms? 

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  • I discontinued my membership recently. Found the skewed data confusing for consistent training.

    Love the social aspect and following pros to see what they are doing daily.

    My couple of euro is going to trainerroad from now on.

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  • Quick note... I also no longer use Strava as anything more than a social platform because of the above issues.  I also would not consider re-joining Stava premium until these are issues are fixed.

    Simple example from 8/20/17:

    Today... I did my normal 20 mile ride.  Garmin has my moving time at 1:08.00 (as does a stopwatch).  Strava has my moving time at 1:08:52.

    also... I did the same ride a few days ago and my time was over 1:14 BUT because I used the Strava App directly it measured my power at 164 watts compared to the much faster identical ride today at 151 watts.  

    This is simply bad math. 

    Strava - your algorithms are wrong (they really are...) and should not supplant raw data being used from another device.  By doing so you lose one of the biggest potential perks of your website, that of riders being able to do apples-to-apple comparisons of their rides.

    maybe stubborn works for your business model and you "know better"; however, from what I have read on this thread (and many other online chat boards) is this attachment to your parsing of raw data is probably costing you real $$.

    like I said...personally Strava is a social platform to me and I enjoy it for that, but I would pay money to join premium if the above issues were fixed.

     

     

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  • Just spotted this myself after starting to pay attention to power data. Last nights ride average watts were the same in Garmin and Strava but NP / average weighted power were significantly different.

    Sorry Strava but that's pants. You're the odd one out. Don't know why I'm posting here as it's clear that nothing is going to happen....

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  • Upload the data from the device & leave it alone. How hard can that be?

    The Strave 'formula', proven inaccurate , also renders the TSS & fitness graph questionable at best. Oh well 'Premium' out.

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  • Well the storyline from Strava gets even murkier. Yesterday I went out on a ride using my new Quarq DFour powermeter, which I connected to my Garmin Edge 1000 via ANT+ and to my iPhone (Strava App) using BLE. After downloading the data from each I looked at individual segments and was shocked to see that the Strava app had effectively cut the power data in HALF! Unbelievable since both devices were reading the EXACT SAME DATA. What the H**L is Strava doing? 

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  • After reading this thread I am discontinuing my premium membership as well. I like the social aspect of strava, but if social is what they insist on then that is all I will use it for. Thanks everyone for persisting in this conversation for over a year.

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  • as with everyone else who's commented here, strava reports a massive difference with the avg power taken from my garmin edge (which is paired to a power meter) out on the road, but reports the same power (within a few watts) after riding on my indoor trainer (latest wahoo kickr) on Zwift. How is it the two seem to agree here? Could the involvement of a GPS be skewing the calcs? It seems that as I'm not physically moving Strava is happy to use the data from the indoor trainer.... I've ridden past a mate in a segment during a ride together (him running Strava direct on iOS, me my Garmin edge) and after looking at our ride still didn't beat him on the day. My comments might not be relevant at all - but then maybe they are????

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  • WTF? It's Jan 2018 and Strava has yet to fix this issue! Elle Anderson spent so much effort in making excuses for Strava when all Strava should really do is let the users upload the raw data to mirror their exact numbers. Glad I didn't subscribe for premium membership only to advertise my false data.

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  • I came by chance to this thread. By curiosity I did some checks myself:
    Indoors Use Trainerroad which records my ride with my 4iiii PM on the iPhone and pushes it to Starva.
    For the last rides (1 to 1h30) average power is identical and weighted average power / NP is +/- 1 watt. The numbers are therefore the same.

    Outside I record with my Lezyne GPS which does not calculate NP on its app. Average power for a 2 hours ride is +/- 5 watts for a 2 hour ride.

    So there is no Garmin involved form me and the numbers are OK. Maybe just maybe it is not only Strava who is applying some smoothing / cleaning?

    Concerning distance and altitude : my GPS has a barometer but it is still sometimes acting up when the weather is changing. GPS signal is not always that good... I use Strava’s correction feature sometimes because it make more sense. But I think there is no absolute truth in any of this data. Maybe strava should propose an optional smoothing that you can activate or disable for each ride record.

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  • For some reason, this is a Rotor specific problem (yet one that doesn't happen on other platforms). I also have a 4iiii precision powermeter on another bike and that one shows accurate data on strava.

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  • Not sure how this happens, me and a friend are both running Garmin Vector 3 pedals, I have single sided, he has double sided. My data transfers to strava exactly as it is on connect, exactly same power etc..., however on his strava takes off 15% of power? Not sure how one transfers data correctly and one not.

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  • Elle and Strava support, what is the timeline for getting this fixed? This is such a simple request: we just want raw power data in Strava. Last night I went for a ride that was 230 avg power on my Garmin (and felt accurate), and 178 on Strava! That's a 50+ watt difference on a 75 minute ride. It's really pathetic that we pay for Strava but the power stuff is useless.

    Please give us an update!

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  • As time trialists we care about every watt we make. It is frustrating me to see that when i upload my data to any platform but strava, i see the same numbers. Only when i upload it to strava i see strange things happening. I'm a Premium, but not for very long i rekon. Time trial efforts are useally giving in the range of 5 tot 10 watts difference in comparison with my garmin. This is a huge difference in longer time trials. This is happening since i ride with a pm and upload my data to Strava.

    Last week i did a clubrace on out local track. Garmin gave me 298 watts for something over an hour and an NP of 351. Strava on the otherhand gave me only 273 watts with an x number of np cause its not possible to see np in rounds on a pay training data analys site?!?! Anyway, direct result of the lower workload is a lower trainingstressscore number and this has an direct effect on the fitness freshness page. This one is now completely skewed. 

    So not only is you analytics off, but all the numbers directly influenced by power are off. This makes strava an completly useless analys tool. 

    Nice for all thos sundaymorning street racers to compare with elite level athletes, but now useless for anyone who takes there training seriously.

    Sorry Strava, i'm out.

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  • It's unbelievable that Strava can't just use the raw power numbers. When will this be fixed? On top of inaccurate numbers, the power curve and fitness/freshness (two hyped paid features) are totally inaccurate for every power meter user. Please fix this. Thank you.

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  • I am using Garmin Vector 2 (double sided), head unit is a Edge 800 or Hammerhead Karoo. Data from both head units are consistent with Connect.Garmin and TrainingPeaks. Strava shows lower average and "weighted" power than Connects average and NP.
    Comparing Strava and WKO data is however interesting: The Power Curve in Strava is next to identical to the one in WKO! The estimated FTP in Strava is very close to the modeled FTP in WKO.
    Seem like Strava is managing this correct, only they
    manage to fuck up the average and "weighted" (NP) values. Why is this????

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  • They don’t care what you think. I reported this over two years ago along with many others. I dumped the paid version and use Training Peaks and WKO4. Not sure who’s running this portion of Strava, but they’ve no doubt lost the company $$ and should be fires.

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  • I have the same with a Stages power meter and a Wahoo Bolt as head unit. Wahoo says avg power 206W and Strava says 178W... Just use raw data as provided by the devices used and leave it alone for the rest.

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  • No doubt.....this is BS....I have stopped using paid STRAVA over 1.5 years to is the way to go!!!

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  • Yep, same here, I just came back from a ride and the raw data from my Powertap P1 via Wahoo bolt says ave power 224w and Strava says it’s 206. Not renewing my paid subscription. 

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  • I just read through this entire thread going back 2 years... seems like Strava never got around to fixing this. I have a left sided stages power meter and Strava consistently underestimates my average power. I’m new to premium membership but will not renew as this seems like an issue they don’t care about fixing.

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