Fit file doesn't start from beginning of Zwift race?

Why doesn’t the Zwift fit files start from beginning of a race? From the timestamps in the fit file it looks like approximately 30 seconds is missing. This hasn’t happened just once, but maybe in every race?

For example, a race starts officially at 7:01pm, but the first timestamp in my fit file is 7:01:32pm. And it can’t be due to clocks being out of sync, since using a secondary power meter matches the Zwift fit file but also shows those missing 30 seconds.

In a short race that 30 seconds can contain a significant amount of information…

I guess it’s the time taken to get out of the start pens…

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It’s caused by the time difference it takes to leave the pens and get to the start point where the lead-in official starts. Past discussions have suggested this is to ensure the race start times are equal for all racers, regardless of whic pen they are in.

Here’s a race that illustrates the point - the lead-in and timer start about 25 seconds after our pen was released. Thats when the fit file starts. I dual record to Garmin and just compared this event between the two fit files and seems right.

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That isn’t true though as your race time starts from the instant you leave the pen.

if you look at the on screen clock as you cross the finish line and compare to result page you will find that leadin time gets added. The video you posted adds about 25 seconds at the end which matches the delay for clock to start.

It would be great if Zwift fixed the on screen timer as they are obviously recording it correctly in the background just not displaying it right

This is for another one I was checking - I’ll do same for the video one later

Zwift FF start 1:12.35
Zwift FF finish 1:49:14
Duration therefore should be 36:39sec

Garmin FF start 1:12:00 (1:11:55 my go to start pace power increases)
Garmin FF finish 1:49:10 (moment I drop power at banner, 1:49:11 power stopped)
Duration difference 37:10
image

So my total effort from pen start to banner is 37:10 (so yes, correct race time is shown) however the fit file is dropping a bunch of time at the beginning almost the same as the time it takes to hit the lead-in/timer start. So OP is correct about not having all his data, albeit its only a ~15-30seconds.

Edit: If I correlate the power between the two fit files, it also validates that Zwift drops the first small period at the start which looks to represent the pen time to lead-in/timer start.

Details matching above vid:

Zwift FF start time 12:32:28
Zwift FF finish time 13:30:18
Duration 57.50

Garmin FF Start 12:32:00
Garmin FF finish 13:30:24
Duration 58:24

Correlating fit files timestamps/power shows first ~30 seconds are missing from beginning of Zwift’s fit file which correlates to Lead-in/timer start

1 Like

I want to echo the experience of other users in this thread. Zwift seems to discard data from the start of races, even though that data appears in the end of ride summary when you exit your ride. I typically notice this in races where there is an extremely hard effort right at the start, and where the start pens area is also larger than usual. Sometimes the difference can be pretty meaningful when evaluating the ride afterwards, if the race starts very fast sub 5 minute critical power can be underestimated by a lot, and also TSS underestimated by a lot as well. It would be nice if this data could be kept in the fit files.

One workaround is to have a separate head unit recording the power from your trainer, but it can be easy to forget that and it isn’t necessarily convenient for everybody.