Versa 3 and Strava show different distance data

[ChiefRimgar]

I have found that there are inconsistencies between Strava and Fitbit when i go on a run. Today i went on a run using both Strava and Fitbit. Strava had put my run at 5.11km, while Fitbit had put it as a 4.68km run. If it were 200m or less i would not be as concerned, but 500m is quite a big difference between them. I used the GPS on my Versa 3 to attain the results and strava on my Iphone. Is there any way in knowing which one is more accurate. I mainly bought the Versa 3 for running and other sports, so if it is not accurate there is little to no point in me keeping it.

Moderator Edit: Clarified subject

[MarreFitbit]

Hi there, @ChiefRimgar. Welcome to the Community Forums. Thanks for the details provided in your post about the issue with your Versa 3. I understand where your concern is coming from. 

Fitbit devices use the formula below to calculate distance. Your stride length is determined by your height and sex. Steps x Stride Length = Distance Traveled

Please note when you track an activity with GPS, your device calculates your distance using GPS data rather than steps. If you begin moving before you get a GPS signal, your device calculates distance using your steps until GPS connects.

To update your stride length, track a run with GPS or measure your stride length manually. For more information, see Can I change my stride length in my Fitbit account?

For more information about GPS, see How do I use GPS on my Fitbit device?

Keep in mind all devices with GPS sensors require a direct path to GPS satellites to calculate location. A weak GPS signal might affect the accuracy of your route and other activity data. Your device uses your step count to calculate distance until it finds a signal, so the total distance calculated for a workout may be slightly less accurate when GPS isn't available for the entire time. To learn more, see GPS.gov.

I've moved your post to the Versa 3 board for organization purposes.

Hope that helps. 

[SunsetRunner]

Hello @ChiefRimgar 

Strava API (that is the interface software with the external services) works in a way that it accepts the GPX (GPS trace) recorded from Fitbit (in this case). In other words the distance measured by Fitbit is not transferred as a number. Because of this Strava takes the GPS trace, tweak it a little bit (for example to remove some obvious error of GPS) and then provide the distance and other related values (pace).

Let's make an example.

You run/walk a certain track and your Fitbit provides you a value of 4.5 km. Fitbit transfer the GPS trace to Strava and measure the distance as 5.05 km but eventually change it to 4.95 km (because few points were considered affected by error, this is very normal).

If you extract manually the txc file from your Fitbit app (you can do from your app) and import it to any website to analyse GPS files (such as mygpsfiles.com) you will find that the GPS measures the mentioned 5.05 km

Is Strava right to correct the measure from 5.05 to 4.95? it might be or it might not be however 5.05 or 4.95 the difference is very marginal and not impacting the actual real result.

Now, back to Fitbit. Why Fitbit says 4.5 that is obviously wrong?The problem is that, as found out by the community since the release of Ionic and never took care by Fitbit despite the many observations, it appears that Fitbit algorithm as its core the distance = stride multiplied by steps. You can understand that the error might be in the steps or in the stride. The stride is particularly affected by many factors such as pace (the faster you go the longer is your stride), irregularity of the terrain, straight lines or curves and so on. It appears that occasionally Fitbit adjusts the stride based on GPS but it is evident that this system is really not logical.

You can check what I say, and that doesn't match what moderators are saying, in 2 ways:

- start your walking/running session while driving your car, you will see that you will measure only few meters based on the steps wrongly measured by your tracker

- run in place, you will see that the distance will increase while it should remain at zero,

Fitbit instead using correctly the GPS when tracking biking sessions (because in this case steps are not a suitable data) so you might want to try to use Biking instead of Running (for sake of verification).

In my case when running I prefer to use another tracker, I still use my Charge 4 at my wrist only to take in consideration the steps and HR for calories consumption but I don't use it to monitor my session because it is really far away from being accurate.