Big watt variations in erg mode

Just to be clear, I’m pretty sure my problem has nothing to do with zwift. I’m looking for help from other people who had or have the same problem.

I have a brand new tacx flux 2 but when I use it in the training mode in Zwift (erg mode on), my power output has a variation of power of 30W. If the erg mode is setted to 150W, it can oscillate from 130W to 160W. This problem occurs on different trainings and I didn’t have it when I was rolling on a Tacx flow (wheel on trainer).

I know it’s not a Zwift problem because it also happens on the tacx app. The trainer seems to be fine since Garmin tried to give me another one and it didn’t solve the problem. Someone at Garmin support said that this was an update issue that made the trainer more precise by removing a smoothing effect on the trainer.
But I don’t see this problem mention by anyone else on internet forums.

Has anyone else experienced this problem recently?

Hi Louis - for your Zwift experiences, do you have power smoothing set to On? The setting is used for display purposes only and doesnt alter actual power delivery. I use a Kickr and the Wahoo app’s smoothing setting does the same.

I found threads that I didn’t saw in first research. A lot of people seem to experience this after havig used a wheel on trainer. Is it a cycling technique issue?

I’ll try to look for a smoothing effect on the tacx app!


I’m definitely not smooth but dont have that level of variation. Its probably a combination of trainer accuracy, pedal stroke and maybe lack of smoothing effect.

Today in the zwift training, it was asking to spin in intervals in a free ride segment. And when I was slowing down too fast at the end, my avatar was completly stop with a foot on the ground. Is that normal? Will smoothing effect correct this?

One more question, can smoothness affect the reading of the cadence as well? When I was spinning, it was sometimes giving me a 70 cadence speed while giving me 110 at other times when I had the impression of going at the same approximate cadence.

Its not normal on my Kickr but could be for your trainer. Smoothening only effects the displayed numbers, not actual. So for example, if you have your power/HR graph on the screen while riding, 3-second smoothing just takes the peaks and troughs out of the picture to look tidier/easier to read.

Hmm, I thought it was power only. But even if it was cadence, that variation seems way off. I wonder if you are also having errors with your sensors not being picked up consistently. Do you use BT or ANT ? One thing to do is minimise anything that uses wireless tech around your Zwift environment. Things like wifi, Bluetooth devices all put out noise that can impact your sensors.

I use BT. A friend of mine also suggested to use ANT. Do you have any interesting ressource on ANT. I would like to know more about it. If not, no worries, I’ll try to find some!
Thanks again for taking the time to answer me!

Just found this - Shane is very clued up on techie things so will be worthwhile content and despite age, it will still be relevant I suspect.

You could see if any of yoru friends have a ANT+ USB dongle (if you are on an ANT compatible device like a PC) to try out. I use some no name ANT dongle I got locally and use it with Garmin HRM, and Wahoo cadence and Kickr. Some people get good results with Ant, some get good results with BT :man_shrugging:

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