Tacx Flow Smart power problems


Just started the indoor season today.
Using the flow smart and new for the season, favero assioma.

I have been using the flow smart for the last indoor season. Really pleased, until i matched it with my power meter. And it is not the difference/accuracy between the power meter and the trainer that is bothering me, it is that the trainer cant keep up with the power demanded by the app/meter.

Example: Ramp test in erg mode. The flow is not able to match power to the pedal. Constantly lower.
Tried again this day with a new workout, deerhorn -4. Same problem. It equals out so the tss is the same in the workout, but the problem is that i constantly are over or under the power i should be at, so i have to change gears. Thought the point with erg mode was to not have to change gears…

See the workouts here:

Anyone got a fix, or do I have to just use resistance mode? :frowning:

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Hi! I’m also a Flow user, since Jan 2018. How did you find it before you got the power meter?

I don’t have a power meter but I do have to use the gears here and there in order to achieve the required power. I generally mean jumping a front ring for hard stomps etc. Additionally, I have to use an easy gear in order to maintain low enough recovery intervals.

This is all down to the limits of the trainers resistance and “wattage floor”. Since I have increased my FTP over the past 10 months I have found a gear that works for nearly everything except 120%+ threshold work, and in that case I just pop up onto the bigger front ring for that period and back down for recovery.

I have exactly the same issue:

  • same trainer
  • similar powermeter (favero BePro)

the trainer could follow target power perfectly before i started using the powermeter whereas now it happens very often that the actual power is lower than the target, even in steady state conditions

is there any way to ask for a fix here on the forum?

I see something similar, same trainer and same power meter (Assioma duo). I just put it down to being a cheaper trainer!

It seems to get you to the power target in the end but does take a while and if I change cadence the resistance doesnt react very well and power drops off before catching up again. Just seems very slow to react.

I was going to do my next ramp test in resistance mode As that was where I noticed it most.

In longer intervals it works fine once it has got you to the target and as long as you don’t change cadence!

mmm not sure that this is because of the trainer quality…
in the end (at least for me) it worked perfectly without the powermeter, so it sound to me more like a control/software issue…

I have a similar issue with Tacx Vortex Smart thought it was fine until I got a power meter then realised somedays no matter what I did with power match it would be under by 10% sometimes over. Sometimes it would track perfectly for a couple of intervals then drift, other times I need to keep changing til I ran out of gears. I found it happened less with Bluetooth from my phone than Ant+ with the laptop. In the end I started using the trainer as a dumb trainer, setting resistance at 65% ish and then using the gears and my PM.

Geez, that’s definitely not the behavior I see with power match on a Kickr Core and PowerTap P1 pedals. The variations you see there are much larger than the TR software shows so it might be specific to your setup or your hardware.

For comparison here is the variation I see with my setup and PowerMatch


Just a shot in the dark here, but I could see simple signal processing and delays being an issue with power match. If you take the Drivo II trainer, for example, it supposedly takes a power reading hundreds of times per second. The resistance it needs to apply is constantly changing, since wattage is a function of your pedaling cadence and smoothness. Our legs aren’t perfect, so it’s not like the trainer just “sets” the resistance and stays there, it fluctuates that resistance constantly to compensate.

That said, without an external power meter, you still get up and down power fluctuations… sometimes only 1-2 watts +/- if you’re really smooth, sometimes it’s 10 or 20w if you’re in the large chainring or are fatigued and not pedaling super smooth. From what I have read on DC Rainmaker, Ant+ FE-C (not sure about BLE) Erg mode works by the controlling device (in this case TrainerRoad) sending the trainer a given wattage to hold. The trainer then holds that wattage until it is given another command; TrainerRoad does not constantly send updates telling the trainer what to do.

Now, you add an external power meter. That power meter is communicating directly with TrainerRoad via BLE or Ant+, processing that signal, comparing it to what the trainer is reporting, and then has to constantly send the trainer updates for wattage. That adds a delay, both for the sending of the data from the power meter to the the phone/computer, TR to process it, and re-send a new signal to the trainer, the trainer to interpret that command, and apply the resistance change.

On top of all that, you can have signal interference which causes delays, micro-drops, and packet loss. You can see this by uploading a Zwift log (if you Zwift) to Zwiftalizer and scroll down to the signal section. It shows you a percentage of data loss, signal strength, and how many times a connection was lost to any of your devices.

From Elite’s customer service: “…you have to consider that the software itself has its “time” (it must acknowledge that the first interval is finished, verify the power of the following interval, calculate the resistance command to send to the trainer and finally send the message). Also, the communication itself has its own delays (due to interference for example).” So they claim that for the Direto and Drivo, intervals under 10 seconds may be too short, due to the all of the above (and actual physical adjustment within the trainer to control the resistance). Adding an external power meter to constantly correct the trainer adds a whole new level of complexity and delays.

I could be way off base here, but I bet this definitely plays a role for some users depending on their specific conditions of devices, trainers, and connection stability.

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@Crownan Before i got the power-meter it was smooth, and i rarely had to change gears. Maybe on some vo2 intervals.
But it was showing the wrong watt though. Got a real surprise when I startet the outdoor season, bought a pm, BAM, 20w drop in ftp.

The problem is though that if I go into a big chainring, the watt is way too high, and wont come down, so say sweet spot work will be waay to hard.

@mclaren121uk This is exactly my problem, with better words.

@sciuste Works perfect without pm for me too…

@Rob1 Exactly same problem as me, but opposite as to phone vs computer, where phone is more accurate for me. I think it is sad that we both bought smart trainers and have to use them in “dumb mode”…

@trpnhntr Your workout seems so smooth and is what I have seen in others workouts too. This is satisfaction, both for fitness and for the mind.

@jmvcolorado Thanks for the insight. I am a smooth pedaler now, but when I started my “career” (haha), I saw what you describe with cadence/power and the correlation when one of those changes. I maybe wrong here, but this should be a quick fix programming wise… And 10 sec delay, as elite cs wrote, is totally acceptable in my head. The problem is when it never manages to find the correct wattage for a whole darned workout…

Hey TACX-employees or TR-technicians. This is obviously a problem for several tacx users with power meters. Could you please share insight or solution if you have? Seriously bad PR for a trainer that cost 350+ dollars.


I have a Tacx Vortex and added Garmin Vector pedals into the mix. Many issues mentioned above then cropped up. The worst was struggling to the end of an interval and the resistance not easing off for some time. I have changed to a magnetic non erg trainer and although it can be tricky hitting exact power it is better than not being sure what will happen next. I could save the pedals solely for out door use but Ilike having comparable power to mix up turbo with outdoor rides.

Edit: I noticed on a trainerroad update this week that a problem with Tacx erg mode was fixed. Tried Baxter and resistance tracked well on powermatch. Happy bunny, I was just about to sell the Tacx

I’ve been looking into this very issue with my Stages power meter and Tacx Vortex and a very interesting thing came up…

I set up a short workout with minute long intervals with varying step sizes so that I could see how small and large steps affected performance as well as how well power tracked at different percentages of FTP.

The first graph shows the power with Powermatch turned on (Trainer in purple, powermeter in Blue):


This shows the power readings from the power meter and the Vortex without Powermatch enabled (trainer in purple, powermeter in Blue):

Finally, a comparison of the two power meter files:

As you can see they are largely of the same shape with the same overshooting when making larger jumps.

I have to say that I find the way the trainer reports the power to be less taxing mentally than when I see the power jumping way too high for a few seconds even although there is very little difference in the power that you’re putting out when the jump is made.


This was really interesting, Mike! Thanks :slight_smile:

Nice to know that it evens out. Good job!

@KingKennedy Same problem here with Tacx Flux S and Favero Assioma DUO on ANT+ connection. ‘Auto’ power match simply ‘does not compute’ well and constantly gives lower power (e.g. instead of 330w it gives ~305w).

Every other workout I try ‘auto’ power match for a while but it keeps giving same low power.
It tracks reasonably with ‘manual’ power match (+11) but not across the board and I want to make it work for my next ramp test.

Is there any solution to this issue?

So, to chime in here, I’m about ready to throw my Tacx Vortex out the window on every single workout. I’m using favero assioma uno, but I’ve tried with a powertap hub and same issues. First of all, endurance power is fine. Any endurance or lower workout tracks fine on ERG mode. In fact, anything below about 270 is fine.

But, when I get above, everything seems to break down, even in recovery intervals.

For example, while doing sweet spot intervals yesterday, my graph looks like this:


As you can see, it’s all over the place, mostly high, during the intervals themselves, and it took almost 2 minutes to come back down to recovery power even with cadence super steady. I way overcooked the workout and was about to quit before switching to resistance mode and finishing there. This is in the big ring, small ring can’t produce enough power with this trainer for anything over endurance, so maybe that’s why endurance works, :slight_smile:

Thanks for any tips!

I have (finally) diagnosed what’s the exact problem in my case (Tacx Flux S + Assioma DUO). During warmup period ERG is all over the place and only after few minutes it slowly starts giving good values as shown in the photo.


I have noticed the same thing if I switch from resistance to ERG during workout - it needs a few minutes to start giving correct values.

It seems to be a quirk with my current setup. Important thing is that it keeps giving good values after the warmup. :slightly_smiling_face: