Apple TV & Calibration Spindown

Hi there.
I have a setup with Flux and Apple TV.
Trying to do a Calibration, but it looks like it gets stuck on part 3, only telling me to keep the speed and keep spinning. Have been on it for 15 min and it still dont go to part 4.

Anyone else have the same issue?

Hi @Bompi_Bjorn welcome to Zwift forums.
Please update your Zwift game app. The latest version 1.0.46903 that dropped on March 27 allows spindown testing on some Bluetooth FTMS trainers like the Flux.

Spindown calibration was disabled for a few months previous to this release, which is why it’s not working for you.

Hi @shooj and thanks for your reply.

I have the latest version of the game app installed.
But i still have issues.

I can start Spindown Calibration, and the two first steps are ok.
But it will not move to step four.

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I’ll flag this up to our QA team for review. Thank you for letting us know.

In the meantime, please calibrate using Tacx’s tool. Their blog shows you how.

Thanks for your help and quick reply @shooj


The QA team reports that it’s important that your trainer is on the latest firmware. Please verify how to on the Tacx / Garmin support site.

I’m told that if the trainer is on the latest firmware and you have the latest (March 27 2020 or later) game version, then spindown in the game app should work correctly.

Would you loop back and let me know if yo’re on an older version? I’d like to relay that to the QA team too.

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Same problems here. I have the latest version of flux 2 firmware and the latest version of zwift on Apple TV. Power drop, fluctuating wattage and can’t calibrate on zwift. No problem to connect my device thought.

I have the same problem.

I have the latest firmware and the latest version of Zwift and I’ve been having mainly two problems (a) considerable wattage fluctuation and (b) cannot calibrate through Zwift, it appears that the app did not find the device; however, it appeared connected.


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Just checked and made sure firmware and app is up to date, and i still get the same “error”

@Bompi_Bjorn @Joe_Gutierrez_R @_acl_Rehab_Michele_D
Thanks all for confirming that you’ve updated the trainer to the latest firmware. << That’s important for anyone in the future who searches their way to this thread. Please do this first.

Our QA team will try to reproduce this spindown issue, and verify the bug. In the meantime - please use the Tacx app to calibrate your trainer.

@bompi @Joe_Gutierrez_R @_acl_Rehab_Michele_D
We’d like to verify something. The QA team asked if one (or more) of you would upload a screengrab of the Tacx app that shows which version of the firmware is loaded? Thank you in advance.

Thanks for verifying the firmware version, guys.

Our QA team checked a Tacx Flux and Tacx Flux 2 on both AppleTV OS and iOS, which covers all three of you reporting in. We were able to complete the spindown test under all combinations of these things.

They gave some info on how this spindown works: once you exceed the speed threshold, the trainer sends commands to the Zwift app via Bluetooth FTMS: a stop command, a success command, etc. These commands are sent only once. If there’s local interference disrupting your Bluetooth environment, it’s possible these commands were not received by the app, and the test gets stuck. This is what we think might be happening for you three.

I took the liberty of looking at the partial log files uploaded to the server for each of you from your latest sessions, and each of your log files are showing different BLE qualities



You can verify by uploading your log.txt file to Here’s how to locate your log files for iOS. AppleTV log files are locked down.

Here are some ways to improve Bluetooth and ANT+ inteference. We hope this helps the in-app spindown test results.

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Hello Shuji,

Thanks for the quick reply. I don’t really care about the zwift calibration, it’s more the wattage fluctuation that bothers me.

I unplugged everything including my router. It’s not interference but I realized I have the same problem using the tacx utility wattage indicator. It bounce all over the place just like it shows in zwift.

I went on Garmin support, many are reporting same problem since months.

I will call Garmin/Tacx.

Thanks again,


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If your Bluetooth signal is up and down, that will also cause your resistance to fluctuate as the signal goes away and comes back.

See if you can eliminate as much of the electrical noise in the area - a fan motor and fluourescent lights are two common sources of noise. Many Zwifters report that shutting those sources off improves droputs.

Having a similar wattage issue with Tacx Neo 2T and Apple TV 4K. Many months with no issue. Noticed it recently in ERG mode. Actual watts too low compared to setpoint in the workout. Pretty sure it’s an issue in a normal ride as a few recent climbs seemed too easy. My working solution is to unplug both Tacx and Apple. I will try to troubleshoot interference. The only change I can think of is the location of my Apple TV and the Tacx transformer on the power supply. Will update if something changes.