Power Numbers Too Low on 2 different trainers

Hey there. We have 2 tacx flux trainers which are both reading incorrect power numbers. Watts/kg will jump from 7, to 1.2, 3, while holding the same cadence and power. The watts are generally WAY lower than they used to be (we’ve ridden zwift for years and know our normal watts.) We’ve calibrated through the tacx utility app and tried doing the same within zwift, but it gets stuck on step 3. I haven’t found any other forums or topics to help solve this. Also internet speed is not the problem as I’ve tested it multiple times.

Hey, I am new here, in fact this is my first post ever, but I hate to see technical issues impeding someone’s ability to do what they want to do, so this is going to be mostly general advice based on some assumptions (which I’ll state) in the hopes that you can do some things that’ll help fix this issue for you. I use an older Kurt Kinetic trainer, Specifically, a Rock and Roll Smart 2, so I’m not at all familiar with your gear, Your mileage (from this response), like your current watts, unfortunately, is gonna vary. Hopefully it helps. I will say upfront that you appear to be reporting two different issues: an interval polling issue where your w/kg is jumping around and a second issue in which your total wattage is down overall.

I’ll start with a question first - in your calibration step above, what is step 3? Calibrating your spindown interval?

Second (set of) question(s): When did this stop working correctly and did anything change? You mention riding Zwift for years. Are these new trainers? Did you physically move your setup? Did you add any new technology into your house / pain cave that could be interfering with the bluetooth connection between your trainer and Zwift? Have you moved the trainers closer together? Do you have any other device paired to your trainer other than the device on which you are running Zwift? Do you / your significant other have each other’s devices paired with each others phones / appleTV / computers?

Without knowing anything else, the sort of problem you’re presenting feels like it would be consistent with an inconsistent stream of data from your trainer to Zwift or potentially with some bluetooth interference.

If nothing has changed in your setup - you haven’t added anything new recently, and you and your significant other haven’t paired each others trainers on your own devices, then I would strongly recommend trying the following:

  • ensure there’s no other tech gadgets nearby that can interfere with the communication between your trainer and whatever it’s paired to for Zwift. Turn other stuff (iPads, computers, burner phones, whatever you have nearby off).
  • ensure your trainer’s batteries (if it has that - mine runs off of a CR3032) are fresh.
  • delete and re-pair your trainer with your device that is running Zwift.

Load up and run Zwift and see if you can resolve or isolate the polling issue first (w/kg numbers jumping around). Go tempus fugit or otherwise super flat area, keep your cadence flat and see what your w/kg is doing in game. If it is still jumping around, make note of whether there seems to be any periodicity to it (is it happening every 5s, every 60s, or seemingly at random).

I think if you can clear this issue that your overall watts issue may come into alignment. Before I write the rest of this novel, I’ll give you a chance to try some of this and respond with more info.

Hey Jesse - I realize this post is from last year, but i’m hoping you might get a notification! Thanks for all the info you provided regarding the technical side of things.

I have an Elite Qubo Power Mag Smart B+ - it’s a non-interactive trainer so it can’t be controlled by Zwift. It does have a build in “power meter” of sorts, so it tracks power, cadence and speed. It’s worked great up until a month or so ago. Now when I ride, my watts are super low, and I know if I were to do an FTP test it would decrease dramatically. I thought it might be the trainer, but I think it’s more technical. I tried it today, and it seemed back to normal. It stays that way for awhile, and then the power drops permanently. So frustrating. I’m using apple tv and the companion app on my iphone, which i set in airplane mode. I think it has to do with what’'s connected, and the internet and bluetooth. I’ve pretty much read anything and everything about this though, and I can’t figure out what it would be.

What I do know is that when I changed the battery, the paired trainer changed from Elite 220 to Elite140. And if i log on to Zwift on my phone instead of apple tv, it connects as Elite Trainer. So odd. I also have no clue how to delete and repair my trainer. I want to start over, but I can’t find any info as to how. I see that was one of your suggestions, so just wondering if you had any advice/tips.


Hey, Lisa! I did get a notification!

There’s an XML file in your Documents / Zwift folder called knowndevices

Make a backup of it (copy and paste it as a new name) and then edit the file and remove the line with your trainer, e.g. delete the line: </DEVICE/>[1] [307743042] [0] inRide 66</DEVICE/>

You can save the file and Zwift should automatically find and re-add it when you next start Zwift. You may also be able to delete the file entirely and Zwift will recreate the entire thing. If it doesn’t work or breaks even more spectacularly you can always copy back your old file.

I don’t know if that’ll clear anything up for you, but it’ll give you something to try.

Editing a file like that isn’t going to be possible on Apple TV.

You could try deleting and reinstalling Zwift. Or if that doesn’t help, factory resetting the Apple TV and installing Zwift again.

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I completely missed that part, Steve. Good catch.