This is doing my head in. And really upsetting my training schedule. Before Christmas, my ERG worked fine. I could hold a steady 5 watts either side of the target, at the correct cadence. There was an update - I have the older Zwift hub, by the way - and now it won’t hold at all. I head to 85 rpm cadence and I seem to be pushing 250W+ when my schedule is asking me for 175. I attach a picture to show you how wobbly this is now. It says I didn’t complete this morning’s workout because it wouldn’t hold steady and it wasn’t exactly a difficult one. I run this off an HP Pavilion laptop. I have updated everything I can think of, including the bluetooth drivers. And moved the wifi away from the bluetooth rays. This is getting ridiculous. The top shows the power wobbling all over the place; the bottom shows how smooth it was before the December update. Please help.
the bottom picture looks to have ERG mode smoothing on which gives you those nice crisp lines. Does the Zwift Hub have an ERG mode smoothing setting like Wahoo does?
I’ve never heard of the Hub offering ERG mode smoothing but I had the same thought about the graph. It is too flat to be real. Looks like a Wahoo trainer with smoothing enabled.
Next time you do a free ride on something flat like Tempus Fugit, slowly ramp up to, say, 90% of FTP and then just ride as smoothly as you possibly can for 5 or 10 minutes. Try to hold your cadence and power static. Maybe do this once a week for 2 or 3 weeks to get good at it.
Once you’ve finally got that nailed, look at the power trace for that last ride on your ride report. That’s as smooth as you can be. Your workouts in Erg mode can’t possibly be smoother. If they appear to be, it’s not real.
Thank you for your advice. I have been using Zwift for nigh on 2 years. I can assure you I am quite good at it. I did not have this ridiculous variation when doing set training programmes before. From 25 August 2025:
If I could upload a video, I could. I use my Zwift for all my tri training speed block work. The lack of ERG hold is new; and the fluctuations in power considerable. I can’t spin at 80W at 85 rpm. If I hit 85 rpm I am pushing a sliding scale of between 120 - 160W. This has only been happening since the December update.
Upload a Zwift log file to trainerdx.com, hit the share button on the report, and post it here if you would like advice about it. You may need to mangle the URL a little like add a space in the ‘https’ part to get the forum to accept it.
Thank you. Really appreciate it. By the way, having Companion App open or not makes no difference. Moving the WiFi router away from the hub makes no difference.
There are no connectivity problems between Zwift and the trainer in that log file. The PC is weak and not performing well (even a phone might outperform it) but my guess is that doesn’t matter for the problem you are seeing.
Did you do any firmware updates to the trainer since you saw those super flat graphs? I’m curious if there was ERG mode smoothing before, because nobody can produce a power graph that flat. It’s something ordinarily seen on trainers that have ERG mode power smoothing enabled (ie, a fake power graph) but I’ve never heard of a Zwift Hub supporting that feature. It’s something you see on Wahoo and Elite trainers, where the trainer is configured to report incorrect power numbers in order to make a pretty graph.
The DC Rainmaker review for the JetBlack Volt trainer says it supports ERG mode power smoothing. The Zwift Hub is more or less a rebranded Volt, almost identical trainer. That makes me more convinced that this is a situation where the trainer was previously doing ERG mode power smoothing and now it’s not for some reason that I can’t explain, but that probably means the current graphs you are seeing are reality and the old ones were bogus.
PC is just an HP standard laptop. And I don’t think there was any ‘smoothing’ before. It just held steadier. The fluctuations were not so rapid. It won’t let me upload a video.
No firmware updates. The Zwift app did a big update. It took a long time to load. I have also uninstalled and re-installed that but no joy.
Really hard to guess what may have changed since nobody said anything about it, but I suspect your trainer is fine, working as it always has just not reporting artificial power numbers in order to make flat looking graphs. If it really bugs you, replacing it with a Wahoo trainer would allow you to get the same behavior as you saw before because Wahoo trainers let you turn that feature on or off in the Wahoo app, but the Zwift Hub doesn’t have a way to do that.
@Paul_Southworth and @David_Galbraith Thank you for all your help. I think, though, I have not explained myself very clearly. It is not the graph that is bothering me. It is the fluctuations on ERG mode while on the bike. If I am doing a set workout, say a VO2 Max session that requires me to hold at 105% FTP for 3 minutes, the ERG should ‘lock’, for want of a better word, me in to that block. Instead the fluctuations are wild and rapid. I can hold a steady cadence of, say 90rpm, but the power will oscillate across up to 100W. The screen flickers between telling me more power and less power constantly - even after the 10s flux; this is felt though the bike, and this is what is driving me mad. As a result, the records are indicated as a failure to complete that block. I note, from a few Google searches, that this is not an uncommon phenomenon. What I can’t find is the fix.
But thank you for all the advice so far. I have again reinstalled the app, uninstalled Garmin Express in case it was interfering in the background. Taken the bike off and cleaned the chain and ensured no friction on the hub.This morning I just used the gearing and I can assure you I can hold the wattage without feeling wild power fluctuations.
