Tacx Flux 2 and 2000W peak at the end of session


I recently upgraded my Tacx Bushido to a Tacx Flux 2.
Since then I often experience a 2000W peak at the end of a session.
Contacted Tacx support and they replaced my device but that didn’t work; still 2000W peak every now and then.
Now Tacx support is telling me this is an Zwift issue.
Anyone experiencing the same and/or has more info on how this could be solved?
Looking forward to your replies.

Johan Barelds

I once had a 2000W spike on my Tacx Vortex. I’ve only ever known it to happen once. Happened when I was a bit late to start an event, and sprinted to catch up. Zwift seemed to think I peaked at 2000W, but it didn’t show up in my Strava upload.

Hi Bernhard,

I am using a PC with ANT+ dongle attached via an extended USB cable.
Go the same info you shared from Tacx support and Zwift support.
Since I already upgraded the firmware and calibrated the devices this won’t solve anything.
Also when I got a new replacement device from Tacx this didn’t work.

I also tried all recommendations concerning possible interference of other electric devices which might cause ANT+ connection spikes.

My guess is that it is a trainer hardware issue although Tacx support is blaming the Zwift software for it. So I contacted the vendor which sold me the trainer and asked them if I could swap the Flux 2 for a Wahoo Core trainer.

I am fed up as a customer being men in the middle between Tacx and Zwift support.
So let’s get rid of the current Tacx trainer and get another brand/type one for which no issues are being reported currently.

Gr. Johan

FYI: there is an workaround to get rid of the spikes in your .fit files. I upload my .fit file that contains the spike to https://www.fitfiletools.com and use the Peak Remover to remove the spike. Just select “power” and “Remove values above” 1500.
Save the updated file and import it into Strava or other tools you are using.

Gr Johan

Hi Bernhard,

Other question: how do you have your Flux 2 paired with Zwift?
I noticed that there are several pairing options for “Cadence”. Flux allows to choose for “Cadence/Speed” but also “Cadence” only. How do you have yours configured?

Gr Johan B

This is identical to what I see. Yesterday, riding downhill from ADZ, I was experimenting with supertuck (which worked). Upon reviewing my Zwift logs on Strava, there were a couple of 2000W surges around the time.

Flux 2 also seems to lose cadence/speed tracking if I stop pedaling (this is essentially the second unit I use. My Flux 2 internals were completely replaced due to noise. The previous one behaved similarly)

This is not a Zwift issue. I’ve been logging this ride with my FR935, independent of Zwift. Sure enough, the same 2000W spikes appear there as well. I will soon be contacting Tacx support, and will update here as appropriate.

Ride on!

Update: Moved from ANT+ to BT; made sure no nearby 2.4GHz WiFi source was active. End of ride: 0 cadence, 2000W.

Still unable to repo unless Zwift is present…

Update 2: Another ride, this time using Tacx training app only (also tracked by ANT+ watch.) Two abnormal high-power occurrences: one 850W BT reported (accompanied by cadence spike), another 1788W (with 0 cadence) ANT+ reported on another location/ride.

Based on the above, I would say this is not a Zwift issue.

Update 3: Another day. Another ride. Tacx app only. Again, high power spikes on both ANT+ and BT.

Another Flux 2 power spiker here. Noticed it when I was experimenting with the tuck as well. However had cadence issues on the climb up too where it was recording a cadence of only 30-40 when it should have been more like 80+. Then on the downhill I stopped pedalling on 2 separate occasions and had the power spike issue. Wasn’t pushing hard before freewheeling just an easy cadence before the tuck. My power on my Flux 2 also reads at least 20w-40w less than my vector 2s pedals but I’ve just put that down to power meter variance.

Just to update you. After being unsuccesful in solving the spike issue with Tacx support and Zwift support, I contacted the online shop where I bought the Flux 2. They where very helpfull in replacing the Tacx Flux 2 for the Wahoo Kickr Core trainer. No issues anymore since. I suggest every one to try to do they same. The Tacx Flux 2 is a trainer with serious issues if used in combination with Zwift.
Good luck all in solving your issues.



I just bought a new Flux 2 and I also have that spike problem at the end of my workouts, 2000W when I stop pedalling and it is winding down…

Had the 2000 Watt spikes on my Flux 2, seems to be resolved since the last Zwift update.

Good morning, trading all the issues on here, my friend is experiencing major cadence issues and 2000w spike issues as well.

Everytime doing the ADZ it returns.
Cadens not going above 42 rpm.

Where to report and find a solution?

I also have the 2000w bug with my Tacx Flux 2.

  • both on ANT+ and BT connection
  • seems to be random, but mostly when going from big ring to small ring…but i also got it several times when riding at a tempo in ERG mode
  • occurs between 1 and 6 times per hour…i think i can’t make a session without having it at least 1 time.
  • last between 0.5s and 3s
  • very ackward when racing…even if i stop pedalling as soon as i see it, it’s still a little uncontrollable cheat :confused:

I didn’t tried a lot but i cannot reproduce this bug when riding on the Tacx App…

I suspect it’s a bug somewhere related between Zwift and the hardware of the Tacx.

У меня также проблема. Не возможно поехать нормально гонку. :frowning_face:
I have the same problem. there is a solution?

There has been a firmware update on recent days for the Tacx Flux, it may help to solve this issue.
You should upgrade it with the Tacx Utility app.

[quote="_Michel, post:16, topic:72714, full:true"]
There has been a firmware update on recent days for the Tacx Flux, it may help to solve this issue.
You should upgrade it with the Tacx Utility app.
I have the latest firmware

I was having this problem but recently changed the “Trainer difficulty” setting in Zwift to Max and have not had the issue since. That is before updating to the latest firmware which I am in the process of doing right now.
Not sure whether this has actually solved the issue or whether I have just been lucky in my last few ( 5-6) rides, not to have experienced it.

Just bought a Flux 2 for my partner, and she is seeing the same 2,000W spike. So far happened at the end of her first ride as she stopped pedaling, and then twice in quick succession at the end of her third ride, which was tonight, this time after she had stopped pedaling. Keen to hear if anyone has figured out why and fixed it!

Update to latest FW version (3.3.40, Flux2).

Problem gone. :slight_smile:

problem still exists for me with the new firmware. Update feels like it more accurately reflects inclines/ declines, but still seemingly randomly jumps up to 2000W. Thought I had sorted it with tweaking the “Trainer difficulty” setting, but that has now be proven wrong.

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I ve got TACX FLUX2 and the SAME Issue !!! Sometimes 2000W when I stop and ride again.
Bought recently, Firmware OK, on iMac and ANT+ … I ve got another issue, when the grade is higher than 5% i must change my gear because the difficulty doesn’t increase.