TSS vs. IF what is more important

Hey everybody,
I have a question about TSS vs. IF which one is more important when it comes to plan your training week. I see that TrainerRoad counts the TSS of a weak.

When I now have a planed week from one of the training plans and I decide to switch to an outdoor ride instead do the indoor trainer workout (weather is fine, more motivating), the TSS of my outdoor ride will be way higher than the one from my indoor ride but the IF will be a little lower maybe. Does this workout still count instead of the planed indoor ride?

thanks in advance,

TSS and IF are very closely related. The TSS per hour for an activity is simply IF * IF * 100, for example, if a 1.5 hour workout has an IF of 0.92, then the TSS is 0.92 * 0.92 * 100 * 1.5 = 126.96

Given that, I think TSS is much better for planning your week - that is one of its main purposes. IF is primarily useful for giving an indication of how “hard” a particular workout is.

In your example, if the TSS is much higher, but the IF is much lower, then that implies the outdoor ride was much longer - if you’re trying to stick to a plan, it’s probably best to have the IF of the outdoor substitute ride be in the ballpark of the scheduled workout.


@badkins, great response. 2 different metrics, with 2 different intentions.

One isn’t necessarily better than they other as they both give a good indication of planned work/effort when viewed together.

Hey everyone,
thanks for the answers. This helps a lot. Sometimes I need to replace a TrainerRoad Indoor Ride with a beautiful outdor ride :smiley: and thanks to the new calender I can now keep track of all my trainings and see my weekly TSS.

Related question. How do I determine the IF for an outdoor ride? This might be complicated for me as I haven’t always used power when riding outdoors and I’d prefer not to rely on perceived exertion to estimate IF.

Is an easy equation: (normalised power/ftp) = IF.
IF^2 * 100 * [duration in hours] = TSS

So if normalised power was 200watts and my FTP is 250, 200/250 equals an IF of 0.8. This doesn’t change based on duration.

If I did this for 2.5 hours: 0.8*0.8 * 100 * 2.5 = 160tss.

If you have a power meter it will calculate this automatically. If not then perceived exertion is correlated to intensity factor and you can use the TrainerRoad estimate for this.

Edit: If^2 not IF

1 Like

Not true. TSS = IF * IF * 100 * Hours In other words it’s IF^2

1 Like


It depends…
You can go zone2 ride for hours all day long to rack up the TSS and it will be beneficial, but you’re not going to be training certain power zones. SO, if your prescribed workout was Bashful (sprint repeats 60s with short rest) and you skipped that to go roll around on the pathways, you will have not touched your Anaerobic system and therefore I would argue you’re miscounting it if you say you did the same workout as the TR one just based solely on TSS.

Now if you went out and did sprint attacks over and over but they weren’t 60/30s efforts but the IF was close…yeah you could count it towards your planned workout.

This goes back to the whole “not all TSS is created equal”, but its not to say you didn’t get some benefit from your 4hr zone2 ride.

1 Like

Hey Rondal,
thanks. This was super helpful. And you are right I try to hit TSS and IF with my outdoor ride but therefore my TSS is always higher, because of the amount of time, which is outside always more. I really try to spice my outdoor ride up with doing intervalls.

Thanks again an have a nice weekend.