Tacx Flux 2 issue

Hi guys,

Hope this topic hasn’t already been covered. I’ve had a quick look at previous posts relating to the Flux 2 and haven’t found anything that is similar to the problem I am experiencing.

So I purchased my Flux 2 just before Xmas 2019 and have exclusively used it on Zwift. To my knowledge both my Flux 2 and Zwift (via Apple TV) are running on the latest firmware/app update.

The last 2 or 3 weeks, regardless of how hard/fast I pedal and using the hardest gears on my 2x11 speed road bike. The system does not seem to be able to offer resistance at anymore than 380 - 400 watts. It seems to work fine at efforts below these power levels so generally fine when cruising during group rides. However, the moment it comes time for sprints, the unit only seems to apply resistance up to 350-400 watts before I notice the Flux 2 stops applying resistance and holds the power at 350-400 watts for the remaining sprint (so frustrating). The same problem occurs in ERG training mode where below the power levels described above the unit seems to work but as soon as the power required reaches above these, the unit struggles.

This was not the case when I first purchased the unit where I was easily putting out between 800-1000 watts on really hard sprint efforts. Anyone experienced anything similar??

Hi @Jeffro_Albania Welcome to the Zwift forums!

I work at ZwiftHQ and I’m looking at your session logs on our server. I’m seeing both an AppleTV and an iPad running the game app, sometimes during the same session. Is that the case?

Are you using the iPad to run Zwift Companion, or the game app itself?

Hi shooj, Correct. I use my iPad for the companion app. The iPad also has the game app installed but I was not aware it was running at the same time.

For troubleshooting purposes, would you try uninstalling the game app from the iPad? Let’s eliminate that as a possible conflict and go from there.

Will do and revert back with feedback…

Fingers crossed its something so simple.

So I did a session on Zwift (apple TV) today after uninstalling the app on the iPad.

The problem remains.

I think I will have to return the unit under guarantee.


Wanted to loop back to this point. I’m going to ask that you download the Tacx Utility app and let’s for sure check that it’s on the latest firmware.

Would you do that, and report back?

For sure shooj , will do mate.

I’ll come back to you this evening.

Hi shooj. Just checked the firmware via the utility app and can confirm I am on the latest firmware.

Let’s assume for the moment that the firmware and software issues are not the root cause, and that your hardware is talking to the game correctly and vice versa.

Would you check something in your game settings? The most immediate variable to solve a “my trainer doesn’t generate enough resistance” complaint is your FTP setting in the game. Too high, and you can barely turn over the pedals in an “easy” workout. Too low, and you won’t get enough resistance when you expect it, such as in a sprint effort, or a climb.

You can bump your FTP number up manually to see if this theory has merit.

A more accurate method is to perform an FTP test in-game. It’s a full-gas test, but at the end of it, you’ll have a measure of your true abilities, and the game will feel more realistic.

Yeah, cheers mate… The first thing I did was do an FTP when I first got the trainer. That was going on 4 months ago now so I should do another one. Question : do I turn off ERG mode during the FTP test? I’m pretty sure it was off the first time. Thanks for your help shooj.

Ah, that’s why your FTP number might be awry.

ERG mode should be left on during an FTP test. The game will control your watt target and raise the target incrementally as it ramps up.

All you need to think about is park your butt on the saddle and keep your cadence high.

Depends what FTP test you are doing. If you are doing either the FTP Test (Long) or FTP Test (Short) then after the warm-up periods the trainer will switch to SIM mode for the test portion (20 min). If you do the ramp test the trainer stays in ERG mode the entire time as it ramps up the watt target each minute of the test and you go until your legs fail you and you can’t pedal/match the required wattage anymore

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So just to be sure…

Do you agree with Shuji that I should have ERG mode on? or are you saying have it ON for the ramp test and OFF when doing the FTP test (long or short)?

Sorry for the confusion

ERG mode is on for all FTP tests. If you select either the long or short FTP test when the 20min block for the test comes up the trainer should automatically switch out of ERG into SIM mode and you ride as hard as you can for a sustained 20 minute period (shifting to increase or decrease your watts, these tests are about pacing). In the Ramp Test your trainer will always be in ERG mode as the test will incrementally increase the required watts until you fail to meet the requirement. Then it uses that point of failure to calculate your FTP

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Great! Understood.

I’ll try to do an FTP test in the next day or so and revert back with feedback.

Hope that fixes the issue and I can avoid sending the unit back.

Thanks all for your input.

I am having the same issue with my Tacx Flux 2. Cannot get the watts over 400’ish no matter how much effort I put in on a sprint. Slower speeds seem to hold resistance just fine. I have recalibrated twice and still the same problem. Firm ware is also on the latest version.

I got this trainer about 1 week ago and my watts have not been the same as my old trainer. On the Saris M2 I could hit 1000 watts on a regular basis.

Jeffro let us know if any of the suggested ideas work for you. I am not sure how to take the game off of Erg mode ect. I an new to Zwift. Any advise is greatly appreciated.


Hi @GMiller

You might also try bumping up your FTP number manually to see if that changes the resistance. You can do that in your user profile.

ERG is only enabled in workout mode, in free ride your trainer will be in Sim mode.

What RPM do you do in a sprint and in what gears are you, what power can you get when going up a small climb? Sorry for all the questions but I could not find your profile on the companion app.do you have a profile on Strava then I can look there.

Bumped up the FTP to: 320

Now able to get the Power up to 529 before it drops out on me.
Cadence at this point is: 85 to 90

I got into contact with Garmin. Sent them copies of the training/riding files from Zwift along with the serial number of the unit and receipt. They are replacing the unit under warranty or allowing me to upgrade to the new NEO T2 with some additional funds. Garmin stated that there is a resistance mechanism that is not working properly. Great costumer service from my experience.

Appreciate responses and the support from the Zwift forums. You’re awesome!

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