What FTP to choose? Favero Assioma vs. TrainerRoad readings

Hi there,

Just took an FTP test. I’m following a program designed by my coach and today I took the 20 min FTP test. It is not exactly the same protocol as TR’s, but similar: only difference is that instead of a 5min all-out (TR), my coach prescribes 3min @90%FTP + 3min all-out. In the end, the goal is the same - depleting my glycogen reserves before the brutal 20 min.

Here comes the issue:

August 2019:

Took the test, same protocol.
Gear: favero assioma pedals, recording data in my Garmin 820 unit + Tacx Flux, following the prescribed workout on Zwift.
FTP results (20min test avg watts* 0,95 / Avg cadence = 78rpm / Weight: 64kg):
Favero asssioma + Garmin - 244W
Tacx Flux + Zwift - 240W
As you can see… not a big deal. Check.

Today - 3 months of “traditional base”, no intensity at all, averaging 10-12h/week on the saddle, following a 3:1 ratio for recovery weeks:

Gear: favero assioma pedals, recording data in my Garmin 820 unit + Tacx Flux, following the prescribed workout on TR this time (I’m a firm believer of placing my money where I perceive there is value… this community + the podcasts & videos totally make me love it better than Zwift).
FTP results (20min test avg watts* 0,95 / Avg. cadence = 78 / Weight: 64kg):
Favero asssioma + Garmin - 260W
Tacx Flux + Trainerroad - 236W
As you can see… Houston, we have a problem.

I already know my coach’s opinion on this, but just wanted to know yours. What could have happened? Have you ever gone through similar experiences? Should I adjust my indoor workouts vs my outdoor workouts (weekends, mostly)?

Curious to read your answers as always :slight_smile: Thanks and have a nice weekend!

One or both of the Faveros and the Tacx either weren’t zeroed properly and/or isn’t that accurate. If you zeroed both then I’d guess the issue is more likely to be with the Tacx. Faveros have a pretty good reputation for accuracy.

In which case since you’re using both anyway I would just use power match so that TR takes the power from the Faveros to control the Tacx resistance.

Other possibility is that you have the Assioma Uno and are getting inaccuracies due to your left:right balance being significantly different in this test to the last.


Ditto on this. Zero or left right balance seems off.

Try the https://www.dcrainmaker.com/analyzer and see if one of them drifts.

or what values did you get for these on both 3min @90%FTP + 3min all-out?

1 Like

I’m using Assioma Uno. Nevertheless, both of you are right with the zero offset. I did it on the Faveros (always do, since they are only left pedal I feel I have to calibrate them often) but not on the Tacx.
I will recalibrate it for the next session and have a 5 minute test or something like that to see the correlation after calibrating both devices.

Could be a drivetrain loss issue too. Faveros are measuring at pedal, but not all of that ends up at the wheel. A dirty drivetrain can cause a pretty big difference.

1 Like

I’ve got the same set up, my Flux reads significantly lower than my Assioma and the gap is not constant but grows with each watt above 180. Since I’m also having trouble with power match I do the following:

  • Have TR control my Flux, record Assioma on Zwift or my wahoo
  • As FTP in TR I use an approximation based on my Assioma readings, because in tempo to lower sweet spot the values are close enough
  • For threshold workouts and higher I manually reduce workout intensity so that my effort matches the prescribed intensity. I’m in my third season and by now know close enough what certain intervals should feel like
  • I import my wahoo/Zwift readings to TP to track TSS

While this is not ideal it gives me all the data that I need and allows me to keep an eye on my power meter data all the time so that my Assioma remains “the truth”.

Let me know how that works for you, TR freezes my Flux everytime I try to calibrate, haven’t been able to figure that out yet.

You don’t make it clear if you have yet to figure out a way to calibrate without freezing or that you have but not why it freezes.

On the assumption it is the former, my advice is don’t use TR to calibrate the Flux. Fire up your Garmin/Wahoo/whatever and calibrate it there before switching it off and running Traineroad.

1 Like

I think my number one input into this would be to not worry about two different power sources being different.

I’d use power match and just go off what your assiomas say. I’m having decent success with my setup of tacx vortex and assioma duos.

Thing is with the vortex is that the reported power changes so much as it warms up. If its colder than when is was calibrated it under reports and if its warmer in overreports. I don’t even bother calibrating it every ride more - just let powermatch work its magic.

1 Like

Kev(?)… With the fluctuation in power reading from the Vortex, does PowerMatch take some time to get to the required wattage on an interval?



It does tend to overshoot slightly going from recovery into an interval.