[BUG] Zwift virtual shifting on Tacx Flux S

[bonillacosas-ctrl]

Describe the bug

Hi, i have the problem with the baseline resistance of the trainer, after pairing all like the tutorials for using virtual shifting once in the game i go down to gear 1 (zwift) , the most light gear and it is very heavy, at 70-90 rpm i put 250w aprox.

I have to say that the virtual shifting works its goes down and up de resistance, but the baseline is very heavy like i said.

I try to going negative gears and the resistance didnt change.

To Reproduce
Steps to reproduce the behavior:

1. Go to '...'
2. Click on '....'
3. Scroll down to '....'
4. See error

Expected behavior

I expect to be in gear 1 on zwift be light gear (have little resistance)

Desktop (please complete the following information):

• OS: Windows 11 Dell Laptop
• Version

Smartphone (please complete the following information):

• Device: Samsung S24
• OS: Samsung IOS
• Version: Android 16

Append a debug log

debug-Mon_Aug_3_23_38_44_2026.log

Additional context

Set up:
-Tacx Flux 2
-Chaingring 44th
-Zwift cog 14th
-Windows 11
-Android 16 phone

Thanks.

[cagnulein]

i suggest to set gears_offset to i don't know -3 or -4 so the gear 1 would be the best one for you
let me know!

[bonillacosas-ctrl]

i tried it, put negative values on gears offset, even stupid values like -500 lol and has the same output (always clicking in the "ok" button)

[cagnulein]

just to be sure could you please collet me one log even of a 2 minute ride where you have for example gears offset -5?

[bonillacosas-ctrl]

Hi, here is the log in -5 gears offset

debug-Tue_Aug_4_19_13_30_2026.zip

[cagnulein]

Hi, thanks for providing the log with gears_offset = -5.

We checked the complete command sent to the Tacx. QZ is applying the offset to the requested inclination, and the resulting value sent to the trainer is very low/negative. For example, a requested inclination of 1.95% is sent as approximately -3.05%.

The Tacx also acknowledges the BLE write: the characteristic is written with response enabled and we receive characteristicWritten for the same packet.

Could you please confirm whether the trainer still feels heavy at the easiest Zwift gear with this setting? If it does, then QZ is sending the expected light/negative command and we need to investigate how the Flux 2 interprets that command physically.

Thanks!

[bonillacosas-ctrl]

Sorry for not write it down, but yes , it feels the same heavy resistance at gear 1 in zwift, even in the app clicking the gears big buttons to a -100 it gets the same.
I tried without get the gears from zwift and has the same result.

By the way i always test the settings in flat roads.

[cagnulein]

just a question, increasing instead make it harder or it seems a fixed resistance? I can't understand the reason, qz is sending the right commands

[bonillacosas-ctrl]

Yes, shifting up it gets harder , with gears gain in 0.2 , at gear 12 aprox it gets imposible

[cagnulein]

are you able to collect a log using zwift or mywhoosh directly without qz following this https://github.com/cagnulein/qdomyos-zwift/blob/master/docs/20_supported_devices_and_applications.md#android-device ?

[bonillacosas-ctrl]

Hi, there it is the test.
I tried to find some "downhill" segment too.

[cagnulein]

Hi unfortunately I can't see the image :(

[bonillacosas-ctrl]

now?

btsnoop_hci.log

[cagnulein]

thanks! let me check it