No dynamic resistance with Tacx Flux S in Zwift

Hello everyone,

I am new in this forum and also new at Zwift. Sorry also for my written English :sweat_smile:
The main Problem is during the drive with my Tacx Flux S. When I drive up a hill the Flux doesn’t change the resistance. At the App from Tacx is all fine.
The second Problem is the calibration. It fails every time. At the Tacx App the calibration has success.

If anyone have an idea I will be very grateful.

Greetings from Germany!

Hi @Yannick_Dierkes, welcome to Zwift and your English is fine :slight_smile:

In the early days with my setup I had problems and it was solved by

  1. Setting up with Trax to do the calibration
  2. Deleting the Trax pairing
  3. Using Zwift, it sorted out the pairing (sort of)

However, don’t waste your time with Bluetooth get an ANT+ dongle after this Zwift and Trax worked together just fine. Until I had Ant+ like you I found Zwift wasn’t great. Now I have it Zwift is brilliant fun :slight_smile:

That is until there is an event important to you, then you arrive almost late to find a Zwift update, which takes a while, pairing also, resulting in you finally get into Zwift a few seconds too late :frowning:

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Thank you for your answer.
I already tried it in this way. By the way I have also an Ant+ Dongle :wink:

Do you have another idea?

Do you use windows or Mac.

when you pair your should pair it as Powersource and Controllable using the ANT+ FE-c option.

See if these link helps.

Sorry no but I hope @Gerrie_Delport has helped, you are in good hands with him.

1 Like

Hi Yannick, everyone,

I’m having the same problem since I have switched to Apple TV (coincidence, I don’t know).

So as mentioned before:

  • there is no dynamic resistance changes (going uphill vs downhill vs flat vs drafting)
  • tried to restart and uninstall all software/apps and also restarting the trainer
  • previously when I have started with Zwift I was using WIN10 on my laptop and was communicating via Bluetooth - everything was good
  • all devices are paired with Zwift
  • even on Apple TV (which has limited number of Bluetooth ‘ports’) my smart trainer and HRM strap are well connected and responding, except the resistance change - which is also shown as paired
  • I have also tried to pair everything on Apple TV via Zwift Companion app - same result - all works nice except resistance responsiveness
  • all settings (e.g. trainer difficulty and others are set up correctly)
  • the thing is that even if I try to connect Zwift via mobile (so the Zwift app is running only on my mobile) the resistance is not responsive
  • I have installed Tacx software and also ROUVY to check if my Tacx Flux S is working correctly - on both apps it works perfectly - so when I’m climbing I feel the change in the resistance etc.

I don’t want to play with ANT+ as Bluetooth was working very well and it works with other apps. Moreover if the app and trainer support Bluetooth - it should work on Bluetooth.

Is there any solution for that or I have to sign off from Zwift permanently and switch to other platform? :frowning:

(PS I would like to stay with Zwift as I was loving it so far)


OK, I have found a solution (I think it helped).
Resistance work as it should and I use only Bluetooth pairing.

Post by [Michael] (Michael_Latsch_DLH):

I recommend that you delete the prefs.xml and knowndevices.xml files from your Zwift folder. These files store your in-app preferences and information about devices that you’ve previously paired. Occasionally, these files can hang on to incorrect information, such as a wrong trainer selection, or a device paired in the wrong spot (e.g. a speed sensor paired in the cadence spot).

Modifying the files in your Documents/Zwift folder can also have unintended consequences, from your avatar appearing on the wrong course to display issues, or being unable to pair your devices, and is something that we generally don’t recommend. When these two files are deleted, they will regenerate fresh copies the next time you launch Zwift.

Here’s what you’ll need to do:
1. Exit and close Zwift. Make sure Zwift is closed from your your dock as well.
2. Open the Documents folder on your computer.
3. Open your Zwift folder.
4. Delete the files named prefs.xml and knowndevices.xml, then close these folders.
5. Launch Zwift again and pair your devices in the correct spots on the Zwift pairing screen, then go for a ride.