Zwift *.fit file strangeness (Century Ride)

(Chuck Kozlowski ZSUNR) #1

Just did a very long ride (over 100 miles). Strangeness is that I completed the ride in under 5 hours (by GPS time - pretty accurate) but the *.fit file says 5 hrs. 11 minutes and change. Since I rode with a fellow rider (Jeff Knisely), I looked at our lap times and the last 11 laps I am over a minute slower as recorded by Strava on each lap even though we rode together. Kind of strange, would certainly have like to have gotten credit for a sub 5 hour century ride today. If you need the strava files I can send the links for the two files.

(Chuck Kozlowski ZSUNR) #2

Looked at the *.fit file. There are skips in the file in the time stamp for each data point that are intermittent, I thought data points are stored every second in the *.fit file. These skips are 2 seconds when they are observed. There are over 1,092 skips which adds up to an 18 minute offset in the file.

(Greg Gibson-Haymarket) #3

This has been reported before. Has happened to me, Scottie, and pretty much anyone doing those long rides.

(Chuck Kozlowski ZSUNR) #4

@Greg, I think I found the culprit and I am just awaiting confirmation from Zwift. The recorded time tags should be on 1 second epochs - there are instances where the time tag skips 1 second and these appear to account for the observed time differences. The good news is that all the raw data is there, just the time tags need to be corrected in the file (if this is indeed the issue).

(' BTCNJ-Jim-HUBS(D)) #5

I had a similar problem . Did a Century on Friday in 5:34 hrs but the upload to Strava had me @ 6:12 hrs . I posted it under Moving / Elapsed time also opened support ticket @ Strava. I thought because of a 20 min. break ,it did not account for but added to my time . Took a picture @ 100 miles
Your findings , explanation makes more sense . Thanks for confirmation . Was thinking of doing another Century Monday morning but may wait until fixed or hear back from Zwift support .

(' BTCNJ-Jim-HUBS(D)) #6


I also had my Edge 500 running in tandem . After deleting Zwift file and trying to post my Garmin file to Strava it gave the incorrect times as well .
When I posted the file to RidewithGps, Mapmyride , Garmin Connect the file reported correct moving and elapsed time . Except for distance which I account for different Circumference inputed on my Garmin then Zwift .

(' BTCNJ-Jim-HUBS(D)) #7

You should open a Submit a Request . Find it top right of page next to your avatar and name .

(Chuck Kozlowski ZSUNR) #8

I set my file to Mathias Krlallman (, I described the problem and he was able to fix my *.fit file and sent me back a corrected file via email. He has a software tool ( but I don’t know if the current version of the tool fixes this particular problem. Now just have to have Zwift fix the problem on their side.

(Chuck Kozlowski ZSUNR) #9

I sent in a report ticket yesterday and I’m sure the Zwift software team is deep into the problem.

(Jeff Doughty PVC WBR (B)) #10

Same thing happened to me on that ride Chuck. More over Strava didn’t recognize my Counterclockwise Century segment because of it.

(Chuck Kozlowski ZSUNR) #11

Send an email to Mathias Krallman ( ) and see if he will help you. He was very helpful in correcting my corrupted fit file. This is a good temporary fix, Zwift will still need to fix the root cause.

(Jeff Doughty PVC WBR (B)) #12

Thanks chuck. I am downloading the program now. I am going to try and do it on my own. I just read the PDF on how to use it. It appears there is a “reorganize timestamp” feature that should reset them to 1 second increments.

(Chuck Kozlowski ZSUNR) #13

@Jeff, let me know if the program works, the demo version is limited so I don’t know if it is going to keep all the original information. Let me know if this works or not.

(Jeff Doughty PVC WBR (B)) #14

@chuck The demo takes half of your ride and enters “dummy” values for the GPS location for half of the ride. Basically a total waste of time.

(Chuck Kozlowski ZSUNR) #15

@Jeff, send the file to Mathias. He fixed my file and sent me back a corrected one.

(Andrew Williams) #16

I think mine only added about 4 minutes