Why does TSS differ across sites?

My ride data is never the same across platforms (e.g., Strava, Garmin Connect, Training Peaks). The ride elevation, distance, average speed, etc. is always close but never the same. I’ve always attributed that to the GPS file and how the platforms parse the data. Why does TSS vary across platforms?

A TrainerRoad workout I did today (Whorl) shows a TSS of 45 in Training Peaks and 49 in TrainerRoad. The TSS is never the same across the platforms.

I understand TSS is an estimate of training stress but shouldn’t the estimated results be the same regardless of platform? Isn’t the TSS calculation a standard calculation?

UPDATE: Subsequent reading in this forum and in Training Peaks suggests that there is more than one TSS calculation and that the data I provide for the calculation (e.g., Max HR, RHR, LT, etc.) determines the TSS. What is Trainer Road basing it’s TSS calculation on? The only information I’ve been asked for is weight and FTP.

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Make sure your ftp is the same on all three sites. All of my rides, indoor and outside, have the same TSS on Garmin Connect, TrainingPeaks, and TrainerRoad.


The short answer: TSS is only dependent on your power output, and your FTP. Usually the differences between sites comes from different ways of handling gaps in the time/power-series, i.e. stops.


building on that, when my TSS differs between sites, its because one of the sites (usually TR) has updated my FTP (ramp test) and I have to manually update my FTP on the other sites (Garmin Connect and TP).

I occasionally see differences, for example on September 29th I did a long outdoor ride recorded on my Garmin Edge 520:

  • TR = 298 TSS
  • TP = 301 TSS (minor diff, ignore)
  • GC = 368 TSS

seeing that difference, it was obvious I forgot to update FTP on GC after my September 25th ramp test. After updating GC, for new rides there is now TSS agreement across the 3 sites.

Note: in TP you can update FTP and “Recalculate” a previous ride in case you forgot to update FTP. However I can’t find a way to do that in Garmin Connect. Its not a problem with TrainerRoad, because all my FTP updates are done in the TrainerRoad app.

Thank you @bbarrera and @michaelbing. I appreciate your replies.

This. Anytime I’ve had a discrepancy of more than 1-3 tss, I had inconsistent FTP settings.