Zwift reported power fluctuates

In the last two workouts I’ve done, there’s been in a difference in the behaviour of Zwift. Even though the trainer feels correct, and is maintaining a constant resistance, the power reading on the Zwift UI is not stable at all.
Previously it took about 10-20 seconds to stabilise on the correct power, and maintained that level for the duration of the interval, but now it’s just constantly going over/under all the time. It tells me the trainer is in ERG mode, which as I say, it feels like it is. Just that the Zwift reported power is not stable.
Anyone know what’s going on?

Any chance that you somehow switched from “3 sec(ond) ave(rage)” power reporting to “Instant” in the in-game settings?

Just checked this. It’s on 3 second average power setting.

Hi Andrew

You are not alone - I could never get all the stars on my workouts due to this. I’ve given up trying to switch everything off EG all other bluetooths nearby and moving the router etc,etc, I just freeride and do badges now. Good luck sorting this.

Yeah sorry to hear about your persistent problem with this, it could really make this app a lot less useful for me, as I’m doing 90% workout plan sessions.

The annoying thing is, up until the last two workouts, it was behaving perfectly.
But an update: this morning I used the Wahoo app (I have a Kickr Snap). I noticed that the ERG smoothing setting was switched off. Now I could be wrong, but I’m pretty sure that was previously on. Anyway after switching on this setting, I tried a workout session and the power was stable.

However the thing that still confuses me, the ERG smoothing setting is for stabilising the power reading during acceleration/deceleration. But what I found on these bad workouts was that the power value was all over the place, literally ALL of the time. My suspicion is still towards a problem with the Zwift app.

GPLama has a video about Kickr ERG smoothing. Remember that every pedal stroke is an acceleration… That said, the workouts you did (especially on the 1st) do not look like ERG was even activated. The power profile is all over the place! Are you really really sure that ERG was activated for those workouts? Perhaps the next time you’re in a workout (during the warmup block), toggle ERG off and then back on again using the bottom-of-screen menu?

Yes that’s exactly what I did during the workout. I thought, is ERG actually on here? So I checked via the menu, and it was on. So I tried switching off, then on again. No difference in behaviour.
But I agree, it does look like ERG was not engaged at all, the power is all over the place, not controlled at all.
But the strange thing is, that the resistance I was getting from the trainer was constant, even on uphills, so I believe the trainer was in ERG mode. Certainly when I finished the workout on a 10% gradient, I could feel the difference as it went into normal mode! :wink:

Hmmm… You will feel a difference riding a “10% slope” between workout and free ride whether or not you were using ERG for the workout, since in general workout mode artificially flattens the route.

There was a suggestion by Mike_Rowe on another thread a couple weeks ago, which I think you saw—but I don’t know if you’ve been doing this or not (?)

…do … a spindown with the Wahoo Utility app on your phone. Then disconnect from your phone, force close the Wahoo app, and fire up Zwift. Do that about once every 2 weeks

(referring to calibrating your Kickr—not sure if it’s a solution)

Generally, are you making sure to quit the app every time you ride? This seems to cover a few seemingly random quirks. Otherwise either there is something obvious that is being overlooked, or it’s a conundrum.

I use the Wahoo app to do a spindown calibration before every ride.
Yes indeed, the workout mode will engage ERG and artificially flatten the route. But my point was, I could really tell when the workout finished and ERG was disengaged. So I don’t think it was the trainer at fault.
Yes I quit the app every time I finish riding.
As I mentioned, the ERG smoothing was off, so I switched it on. I’ll see how future workouts go.
Thanks for your suggestions.

I won’t belabor the point any further, except to reiterate (in case I misunderstood) that all workouts (with or without ERG) artificially flatten the route, so the fact that you noticed a big difference at 10% slope between workout mode and free ride mode doesn’t suggest per se that ERG mode had been activated—only that the workout had ended.

Hopefully someone else with more / better information will chime in—best of luck.

Ok I see your point. It’s just that Zwift was telling me that the trainer was in ERG mode. Plus the trainer resistance felt like it was at a constant setting, which kind of confirms this. I don’t really know what was going wrong here, and the previous comment about other people having the same problem leads me to assume it was caused by an issue with the Zwift software.

For anyone else who got this problem with a Kickr Snap trainer, I used the Wahoo fitness app, selected the connected trainer, and set ERG smoothing to on. Problem solved.


Thanks. I’ll try that. My power readings were all over the place this morning. It was the first time I tried the workout mode.