It came to my attention that doing a track calibration test with your Stryd power meter isn’t as simple as go to a track and run a few 800’s.
It requires some prep work and an understanding of the different data pushes you may have synced up with your watch, Garmin, Power Center, etc.
First, why would you want to calibrate your Stryd?
GPS, as we know, isn’t a perfect measurement of distance and real-time pace. It’s definitely in the ballpark and can be pretty close on certain days in the right circumstances. But at its worst, you can experience data dropouts of screw-ups (we’ve all had them – crediting us for our fastest mile when we weren’t even trying to run that fast). If you are data dependent, it’s definitely wise to have a few sources (just in case). My buddy Andrew experienced that on his run today and was shortchanged on many of the important power related metrics for his intervals because of an errant GPS file. Once he plugged in the Stryd Power Center file, it was far more believable and in line with what we normally see in WKO4.
Also, it is commonly known that Stryd comes out of the box REALLY WELL calibrated without the need for adjustment. But there have been cases where it is generous with distance and pace estimates, and if you rely on it for those during a race, you are making a mistake. You should definitely test its accuracy at a track first. I recall a friend who ran a marathon (I also read a similar story from a fellow blogger) relying on his Stryd measured distance and pace estimates and was not pleased when he finished and saw 26.8 miles. Even if you think it’s close (there are ways to compare it to GPS files, but this isn’t the best approach since we know GPS isn’t 100% accurate to begin with).
With that said, let’s get on with how to do it and learn from the mistake I made.
The first thing is to make sure your calibration is still set to the default value of 100.0.
Then, pick a day where you can find a local track and make sure your watch is configured to use STRYD as your speed source (“Use as speed source – Always” is in the sensor setting). I would also turn GPS off as well because it will override the above configuration in most watches. Alternatively, you could just use your watch in indoor mode, and that would do the trick as well (probably the easiest way to go about doing this). In this scenario, you will lose your map on your run file.
The reason you need to do this is (and I learned the hard way here) is because if you leave GPS on when your run is done, your Garmin pushed file (which should contain power) will contain GPS measured distance for each lap you take! You want Stryd measured distance – thus allowing you to change the calibration (if needed). I made the mistake of setting a calibration value off GPS data and then when I went to test the new calibration value the next day, the results were even more off. Lesson learned.
Once at the track, you can run several laps, staying in Lane 1 about 12 inches off the inside line. That should measure out to 400 meters exactly if you run it correctly for each lap. I recommend switching up paces and doing 400s, 800s, 1200s and making sure you are hitting the lap button with each distance.
You will then be able to see the Garmin pushed laps with the Stryd measured distance.
Here is how I have my push settings for all of my sites:
Garmin pushes files to Strava, Final Surge (for my Coach), Training Peaks (I rarely use this now but when I did, it was for the Threshold notification) and Power Center (I like having 2 files, the raw file from Stryd and the Garmin file – more on this in a bit).
Without you pushing the Garmin file to Power Center (even if it’s just once or twice for the track calibration tests), you will have no way of knowing when you started and finishing your intervals with the raw fit file (I’ve never had to use the app so I can’t say with 100% certainty that they have a lap button on it but imagine trying to do that with a phone on the track. It can be done but it won’t be pretty).
The other way of checking out how many meters each lap is, is if you have WKO4. You could simply load your Garmin pushed file, and the laps will be evident.
However you go about it, you can see how many meters are being measured per lap and settle on a calibration value.
What’s the formula for determining the newly calibrated value?
(Actual distance/Recorded distance) * Old calibration factor = New calibration factor
example: (400/403 = 0.992) * 100 = 99.25
Having said all that, I’ve seen a fair amount of track calibration results and most come in <1% off the true distance.
If you train by power, distance and speed isn’t as important as it used to be. It’s more about training stress (rTSS) and time in your zones. However, the accuracy of speed (distance/duration) is critical if you are fully utilizing Running Effectiveness in your analytics.
I still like monitoring pace and distance after the run even though I only have power on my data screens (along with lap time) so it would be nice to have accurate distance and pace.
How do you know if it’s accurate after you set your new calibration value? Go back to the track and run another few laps following the same protocol above and see how the data shakes out. If you can get within 1%, you’re pretty damn close.
1) Configure watch for track test
2) Run on track at various distances/paces, manually lapping each one
3) Check your data source and make sure it is not reading from a GPS file
4) Plug your numbers into the calibration formula above and set new calibration value
5) Repeat track test to confirm new calibration value