# TSS Discrepancy

This Saturday I did a Zwift team ride https://www.strava.com/activities/4371128473/overview
TR gave me a TSS score of 218 for the 2.5hrs at 229w, about 80% of my FTP which is currently about 270w.
Today I put a similar ride on my calendar for next Saturday and set the estimated stress to tempo. TR only estimated 129 TSS. I had to set it to Race Pace to get TSS to 208. Is this really correct? Was my 80% of FTP race pace? It sure didn’t feel like it.
Thanks for any input

Something is wrong by the math;

.8 x .8 x 100 x 2.5=160 TSS

TSS uses NP, not AP.

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218 TSS in 2.5 hours means that your IF was 0.93 and your VI was 1.16. If your team ride had lots of changes in effort, then that seems about right.

129 TSS in 2.5 hours means an IF of 0.72, which is in the endurance range. This is the calculation that seems off, then.

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That makes more sense after looking at the Strava file now. Weighted average power (Coggan Formula) in Strava is usually close to NP for the ride. In this case it’s 252…252/270=.93.

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OK that makes sense. So another question then is when I add TSS manually to a ride I did without a power meter, that TSS is likely off, maybe even by as much as 100 points?

What’s this formula you are using?

IF x IF x 100 x duration

IF - intensity factor which is NP/FTP
Duration in hours

Like @old_but_not_dead_yet said you need to use NP (normalized power) and not average power

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Strava uses xPower (25s rolling average) and Relative Intensity (xPower/CP). It’ll be slightly different (TSS vs BikeScore).

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Ok cool, thank you. I’ll have to think more about how the ride actually was when adding tss for the rides I do without a power meter.
Thank you so much for your help

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I don’t have any advice on estimating TSS, always had a power meter for that. Maybe heart rate somehow…

TR does it for you, but you have to put in your effort level. So I’ve been basing my effort on what it felt like. And I’m realizing this is not entirely accurate, as an easy ride is not easy if it has hard efforts sprinkled in. So I just have to give more thought into imagining what my normalized power would have been.