Hi,
I just saw that my workout is shorter on Strava than in TrainerDay or Apple Health. Since it’s late, I haven’t looked yet if this is the only workout.
Any suggestions?
Do you need more data?
I’m on iOS 18 with TrainerDay 5.0.2
Are you using apple watch by chance? TrainerDay app does not have speed or distance but when we send it to our website then the website calculates speed and distance. When it goes to strava and you have the map turned on in settings then it will add a map that it applies your power towards to determine speed and distance. You can turn off this map in strava connection settings.
Hi Alex,
yes, I’m using the Apple Watch.
I rephrase a bit to make sure that I understand the behaviour better. And I guess my text wasn’t clear enough. It’s about the distance (kilometres) not the length. I’m sorry. 2nd language issues 
TD calculates the distance (and other values) and Strava calculates the distance again (but differently) und this explains the difference of roughly 10 kilometres in my last ride?
But I still don’t get the connection to the Apple Watch. I’ll wear the Wahoo Fit for the next workout.
I also don’t get the Strava map option, but I know how to de/activate it.
Next workout: no Apple Watch and no Strava map. Fine for me, I’m curious 
BR,
Andreas
Sorry you did just fine. I understood what you meant length = distance… So I am not sure exactly how your data is flowing in this case but let me explain how this works and it might better help you understand where the difference is. Your trainer outputs speed and distance, the problem is this is based on rotational speed of the rear flywheel. So this is a bigger problem in ERG mode because you can change gears on your bike, the flywheel goes faster but the power stays the same. So we ignore the speed and distance and calculate it ourselves based on power, you and your bike weight. So this calculation happens on our web server before we send the data to strava.
If one of your other recording devices is pulling the data from the trainer itself there will be a difference in speed and distance.
These values below determine the conversion from power to speed. Generally this is a very accurate conversion.
But if you want to make an adjustment to Drag Coeff for example you can try to get the values to match more closely.
This is why I mentioned apple watch as apple watch might be taking this data directly from the trainer which as I said can very inaccurate in ERG mode. You also can just change your gearing to try to get the values closer but in either case you should not shift gears once you get it matched
