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Strava 'adjustments' to Garmin files
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natethomas
May 3, 17 8:37
Post #1 of 6 (1187 views)
Is anyone else seeing Strava sometimes adjust lap times, especially when running? I did a track workout this morning, and the lap times for miles didn't jive between what my Garmin read and what Strava has. Does Strava somehow autocorrect for distance at a track?

My workout was 2x3 miles and, while not hugely different, the times are slower on Strava by around 4-5 seconds per mile compared to Garmin Connect. This isn't something I'm concerned about, but I'm just wondering why the discrepancy???

I've also noticed that power #'s are sometimes different on Strava - usually NP is lower on Strava than in the Garmin file while AP is the same.
Blog: http://262toboylstonstreet.blogspot.com/
https://twitter.com/NateThomasTri
Coaching: https://bybtricoaching.com/ - accepting athletes for 2023
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Re: Strava 'adjustments' to Garmin files [natethomas] [ In reply to ]
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racehd
May 3, 17 9:13
Post #2 of 6 (1140 views)
Quote:
Strava takes the same file off the Garmin, but we enter and parse the data in our own system. We enter all the numbers, then calculate out the time, moving time, average speed, segments, etc. with our own algorithms we developed.

https://support.strava.com/...imes-than-my-Garmin-


Personally I'd turn off auto lap on your watch and just manually hit the lap button when you finish a mile. Then you know your laps are each one mile and you can ignore what strava tells you.


You could try turning on 1s recording which might help (as opposed to smart recording). Basically what happens is you are running on a track and the GPS signal might not be 100% accurate so it captures one point, perhaps on the inside of the track, and then the next point is on the outside of the track. Or just in general taking a corner it may not get all the points in between and just see a straight line cutting the back corner in half. DCRainmaker has discussed this at several points on his website over the years, both in dedicated articles, but also within device specific in-depth reviews.


And perhaps overkill for what you're wanting, but TTF had a thread from 2015 that discussed course measuring devices after a well ridden course was determined to not be the stated distance. The thread discusses measuring devices (including Garmins) and the accuracy and tolerances of these devices. http://www.timetriallingforum.co.uk/index.php?/topic/105492-course-measuring-devices/& . If that sounds interesting to you, it's a pretty good read and will at least make you question the true accuracy of your GPS. That is why Garmin and Strava have their own algorithms to "correct" the data as much as they believe is necessary/possible. That is also why I suggest if you're running on a track to turn off auto-lap and manually hit the lap button yourself for each mile (or more frequently if you need the splits). The reason being when you are on a track you know the distance, so there is no need for the GPS other than to get a few internet points on your strava page and tally marks in your training log ;)


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Re: Strava 'adjustments' to Garmin files [racehd] [ In reply to ]
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natethomas
May 3, 17 9:22
Post #3 of 6 (1122 views)
Thanks for the detailed response! I guess no need for any more answers.
Blog: http://262toboylstonstreet.blogspot.com/
https://twitter.com/NateThomasTri
Coaching: https://bybtricoaching.com/ - accepting athletes for 2023
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Re: Strava 'adjustments' to Garmin files [natethomas] [ In reply to ]
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g_lev
May 3, 17 10:19
Post #4 of 6 (1040 views)
natethomas wrote:
I've also noticed that power #'s are sometimes different on Strava - usually NP is lower on Strava than in the Garmin file while AP is the same.

Regarding this: Strava's "weighted average power" isn't the same algorithm that Garmin uses to calculate NP.
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Re: Strava 'adjustments' to Garmin files [natethomas] [ In reply to ]
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tkos
May 3, 17 10:39
Post #5 of 6 (1013 views)
Strava rounds numbers down. So 1.03 miles would be 1 mile. (well it is in kilometers anyway). That can sometimes effect avg speed calculations. Strava does all sorts of fun magic.
Ian
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Re: Strava 'adjustments' to Garmin files [natethomas] [ In reply to ]
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NordicSkier
May 3, 17 10:57
Post #6 of 6 (976 views)
GPS on a track? Why? Basic chrono for track...
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