Stryd footpod - accuracy and calibration

Hi all,
I've been reading various sources on accuracy of the Stryd footpod, and the opinion seems to be unanimous that it's the closest thing to perfection there is - even without any calibration.

Since I often run under difficult GPS conditions I purchased the Stryd mainly to get better instant pace, but of course better distance accuracy is always welcome.
After a few weeks running with the Stryd I see that my known routes (5-12 km) ends up consistently 3-4% shorter with the Stryd than before when I was using the F5+ GPS as source for dist/pace. When I calculate pace from total distance and total time I get a pace that matches the recorded average pace, so I guess that means that if distance from Stryd is wrong so is pace. (or vice versa) And yes; the Stryd is set to always for both distance and speed, auto calibration off, calibration factor 100.

I've measured the routes on Google Maps - and yes I know it's probably not the best source in this matter - however it matches the distances recorded by multiple GPS runs quite good, and much much closer than the uncalibrated Stryd.

Have any of you experienced anything similar?

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0 bpl1972 over 6 years ago

Interesting. I'm getting my Stryd today and going for a run on Saturday. I will lookout for the distance/pace on a route I have run before...

0 AllanOlesen67 over 6 years ago

If you look in the Stryd forums, you are not the only one who needs a correction of +/- 4-5%.

In my tests with the current firmware, I had a slight speed dependency, requiring a calibration factor of 98.5 at low speeds and 100.7 at high speeds (high for me, that is). It can be discussed how much of this was caused by my test protocol. Anyway, with these results I stick to a calibration factor of 100.0.

More in this thread, post #20:
https://club.stryd.com/t/is-calibration-factor-speed-related/10377/16

0 SAHO over 6 years ago

Thanks Allan, I wasn't even aware of the Stryd forum, but now I will certainly do some reading over there!
Good to know that it's not only me who sees the need to do calibration - I feared there was something wrong with my Stryd since there's so much focus on how good the Stryd is out of the box.

Unfortunately I don't have access to any certified tracks or other routes with verified distances in my area. What about using Google Maps measurements as reference for calibration - anyone have any opinion on that? As said, I've found distances measured on Google to match pretty well with GPS measurements from F5+ (and also my previous VA3)

0 Mathias.Bjorklund over 6 years ago

I will suggest you to use an a straight bicycle road or similar with a length of at least 1 km. It should have open sky with no trees and no houses near the road. Set you GPS to auto-lap (distance from GPS) with some interval (500 m) and run with the speed where you want best calibration performance. (race speed?)
Afterwards you load your fit file into Fellnr's calibration tool
http://fellrnr.com/wiki/Garmin_Foot_Pod_Calibration
Then you can look and see what is an appropriate calibration factor. Only look at those laps where the speed diagram looks consistent and ok.

0 SAHO over 6 years ago

Thanks for the tip, sounds like a good approach!

I’ll look for such a test route, but it might be difficult to find a straight like that with open sky and no side terrain/obstacles in western part of Norway :p

Anyways - I guess the logic is to run with as stable conditions as possible over a significant distance with no sharp turns etc ?

0 Teriemer over 6 years ago

Actually, I did a series of calibration runs yesterday with various paces on a 400m track. Stryd is massivly accurate! Just take a look on my numbers:

- 1k @ 5:10 (min/km) -- CF = 1000
- 2k @ 4:35 (min/km) -- CF = 991
- 1k @ 4:05 (min/km) -- CF = 991
- 2k @ 5:10 (min/km) -- CF = 996
- 2k @ 4:35 (min/km) -- CF = 993
- 1k @ 3:40 (min/km) -- CF = 994

I concluded my testing to set Stryd to 995. With that, I'm always within 99,5% accuracy...!

Seriously impressive...!

And note - this was on a 400m track. Don't go with "just" measured GPS the one or the other way. It's just not accurate enough to calibrate Stryd. Use a track if possible.

0 SAHO over 6 years ago

Teriemer I have no doubt that the Stryd has a very high consistency (precision), the issue seems rather to be related to bias (accuracy) and this is where calibration comes into play. Even if the marketing and public opinion claims that Stryd doesn't even need any calibration, I think this discusison (and other sources) has now prooved that that is not true for all individuals, myself included.

Your example is not proof that calibraition is not required - it's simply a proof that you as an individual are really close to whatever Stryd has set as their baseline.

For me, once I've found the correct calibration factor, I'm in no doubt that the Stryd will give me very good data on both pace and distance. At the moment it seems my calibration factor is somewhere in the area of 103,5 (3,5%) which I find quite significant for a device that claims no calibration necessary.

0 AllanOlesen67 over 6 years ago

The "no calibration necessary" claim can be interpreted in many ways. I will just say that for me, an uncalibrated Stryd is more precise than a calibrated Garmin foot pod.

0 SAHO over 6 years ago

The "no calibration necessary" claim can be interpreted in many ways.

Of course it can, but it doesn’t make the claim any more true or universal.

The fact that it’s more precise than a calibrated Garmin footpod says more about how poor the Garmin is rather than the need to calibrate the Stryd. Again, I’m talking about calibration in terms of correcting bias, and from what I understand the Garmin pod on the other hand struggles with consistency at different speeds which hardly can be corrected by a fixed calibration factor.

That said, I don’t see the need to elaborate any further as I’ve got the answer I was looking for. Thanks for everyones input!
:)

0 fkelsch over 5 years ago

I have to change my calibration factor close to 104. I had checked against a course I measured with a calibrated wheel. The claim of Stryd that it is accurate out of the box makes no sense to me as an engineer since people are all different and there is no way Stryd can take into consideration all he variables of how people run. No doubt a calibration factor of 1.0 is just right from some people. GPS is also accurate to check against if you go straight, with no trees, and far enough. Most Garmin units are accurate to within 5-10 meters so over a long enough distance that becomes a very small percentage. Garmin footpods are also more accurate than some people say.