Tacx Flux 2 Power Issues

I have a Tacx Flux 2 that I have had for about 6 months. I also have a pair of Favero Assioma Duos.

The Tacx reads lower than the Duos. This in itself is not unusual I realize. However, it’s not the standard ~20W drive train issue. I’ve been seeing fluctuations sometimes as high as 100W. So I did some testing the other day. Here is what I found, running each power over an interval of a minute, with the Tacx reporting directly to the Tacx app and the Faveros to my Element Bolt.

At 100W - <1% variance in avg power
At 150W - 1% variance in avg power
At 225W - 8% variance in avg power
At 337W - 14% variance in avg power

This was in Erg mode. So with the TACX thinking I was steady at 337W, the Faveros were measuring 384.

I can tell you that this trend keeps going, but I didn’t feel like blowing up my legs as I’m supposed be at the end of SSB II with an FTP test pending this coming Tuesday to start my build. Obviously, I’m not going to be able to get an accurate FTP test in Erg mode.

FWIW, its not the Faveros. I’ve tested and found discrepencies with other power meters on the TACX, though I didn’t do this level of side by side comparison.

I sent the files corresponding to my test with TACX support. Their response was ridiculous.

"With 3rd party power meters there can be up to a 20% difference in power numbers.
This is due to the point where the power is measured with the flux 2. "

Here is a link to a recent test I did illustrating the issue:

Anyone seen something similar?


I have the flux 2 too but, compared to my quarq xx1 PM they are almost spot on in terms of power… slightly 3-4-5W lower than quarq.
I compared those to in a 30-40min test in zwift(sim mode) but below 300w effort.