Outside TSS (for casual rides) seems like an overestimate

I often get similar TSS values for a physically/mentally challenging inside workout as I do for a very relaxed ride outside / commute. Outside TSS is based on HR as I do not have a power meter on my bike. I assume I am not the first to notice this, but could not find a similar thread on the Forum. Am I the only one?

First question, have you set up your HR zones?
Second question, how long are your outdoor rides? As TSS is calculated with a time multiplier, an easy, but long outdoor ride can have fairly high TSS. (For example you might ride an hour to a cafe, 90 minutes with a mate, another hour to the pub, half an hour home, and you’ve done four hours.)

Thanks for your input! I did set up my maximum HR in the TSS estimation settings. What I see applies to both long and short rides. For example, yesterday I did a 3:30 hour tough MTB ride (233 TSS), then I did a very easy ride with my wife, for about 1:10 (49 TSS). The second ride feels much less than one fifth of the MTB ride, and much much less than 50% of todays pine mountain (106 TSS, 2:30 hours … which really had me working). I understand that integrating over a long time can yield high scores, but I sense that they do not accurately reflect training stress.

The TSS formula: TSS = (sec x NP® x IF®)/(FTP x 3600) x 100


  • “sec” is duration of the workout in seconds,
  • “NP” is Normalized Power® (don’t worry about this for now),
  • “IF” is Intensity Factor® (a percentage of your FTP; in other words how intense the effort was),
  • “FTP” is Functional Threshold Power (your best average power for a one-hour race or test),
  • and “3600” is the number of seconds in an hour.

If you don’t have power, you are using HR to get at NP, IF, and FTP. Not sure what software you are using and what their calculation is, but it is clearly not working well given your results. Maybe just do your own estimation using the table in this article - Estimating Training Stress Score (TSS) | TrainingPeaks.