ERG mode on Zwift =/= ERG mode on TR?

As far as I know, the ANT+/BLE specs do not have provisions for a power-match mode; this mode is done by the app placing a bias on its power demand (i.e. sending “z” rather than “x” as a power demand, to use your example above). Since the difference between x (the power required by the app) and z (the biased power demand that will cause the trainer to set a load that is then measured by the power meter as equal to x) is not constant, the app must incorporate a secondary control loop to iterate on the proper value of z. And thus yes, the trainer receives a constantly-updated power target. The “much longer time scale” is not necessarily this long; most good trainers can closely match the power demand in erg mode within 2-3 seconds, and the power match loop closes in within 5-10 seconds - this is based on the observations of the examples posted on this forum, and has no pretense to scientific facts…

I could confirm my starting hypothesis (about the ANT+ spec), but don’t really have the time now.

Ant knows nothing about power match, that is true.

As to the loop being small. Pretty sure it isn’t. Some people may be very good at putting out smooth power numbers. Power match is easy for them. Others? Not so much. It’s not just the hardware that is involved, is a person’s legs too. See https://zwiftpower.com/analysis.php?set_id=39686

Quick update on this issue. I’ve been noticing more knee pain with ERG on Zwift, I ended up switching to standard mode in the middle of a threshold workout. Strangely, standard mode felt “easier” than ERG :man_shrugging:.

In ERG mode I couldn’t really hold a cadence over 88RPM and it felt like I was fighting the trainer or pedaling through mud, not sure if that makes sense. When I switch over to standard I was spinning comfortably at 92 RPM but still able to hit my target watts.

Just for posterity’s sake, I calibrate my Favero Assioma Duo’s before every ride and perform a spin down on the Wahoo Kickr about once a week, usually post-ride because I keep forgetting that Wahoo wants you to ride 10 minutes before doing the spin down :stuck_out_tongue:.

I’m probably going to do my workouts in standard mode from now on, which is a bummer because I’m not good at hunting for gears and it throws me off a bit. Does anyone know why it seems harder on ERG mode? Is it a power disparity between the Kickr and Favero’s?

Thanks!

Swapping to Resistance would likely mean a change in gearing, and potentially a difference in flywheel speed. That can be a big factor in feel.

  • What gearing are you using in each of the two setups (ERG vs RES modes)?

Additionally, the difference on “loading” between ERG & RES can lead to different impact on the muscles.

  • Do you have a workout to share with the switch in place? Would be interesting to see the power graph between each mode, for equal effort and duration blocks.
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Thanks Chad!

In ERG I’m using 50x17, in standard I’m at 50x19. Can you see my workout here? I switched to standard mode almost immediately after the first interval.

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I have only done a couple of erg workouts on Zwift with my Kickr, but with my Quarq set as power source, it does feel “laggy” compared to TR erg mode. I think the control loop between Zwift setting a target on the trainer, and measuring the power on the PM is just slower. Somehow this makes it feel harder to maintain a given power when it seems to be correcting all the time.

One other option you could try is configuring your Kickr to use the Assioma pedals to control erg mode. So in Zwift you would set the Kickr as the controllable trainer and the power source. In the wahoo app on your phone, enable “control erg with ant+ powermeter” option for the kickr, and enter the ant+ id of your pedals.

That should take Zwift out of the loop - it will just be sending a signal to the Kickr saying “erg:250w” or whatever. Then the kickr should read the Assiomas to check it is on target. If you try it, let us know if that setup feels any different. :slight_smile:

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Yes, I can view the workout. I will take a look and see if anything jumps out.

Edit: Nothing obvious jumps out at me.

  • Your cadence is consistent within all intervals, so much so I wonder if it’s smoothed? Just seems there would be more cadence change for the power fluctuations I see, especially in a 10 minute long interval. Not sure it really matters, but if it’s smoothed, it may be masking variations that could be part of the picture. Perhaps it’s just the real relationship between solid cadence and the erratic nature of power, especially from pedals (which are the most active).
  • Average power and overall range within each interval also look solid.
  • Considering you only changed the gearing one cog, I don’t see that as much of a factor.

Sadly, I don’t see any clear differences to draw conclusions.

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Thanks again, Chad!

I have 3 second average for power turned on for Zwift, but I don’t know if that also smooths cadence. I’ll keep using standard mode because of the knee-pain issues from ERG.

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X, y, z… so, when you do a ramp test on TR, is it best to use the number spit out, or to adjust it according to any known or observed offsets?

Specific example: using a Tacx Bike Smart trainer, if I ride an interval in erg mode at a relatively steady cadence near my FTP then I get a 2-4 watt delta between target and average power for the interval (average is lower). With that in mind, when I do a ramp test should I use the reported FTP result, or use a number 2-4 higher?

Interesting. I was going to make a post about this today as I experienced something similar.
I been a zwift user for years. I always use ERG mode.
Today, I did my first trainerroad workout in ERG mode. It felt markedly different than zwift. In a good way.
Much easier to keep a high cadence and to accelerate than in zwift erg. Very strange. I had no issue holding 90+ and close to 100rpm very as in zwift below threshold efforts I am generally riding in the low 80ties.

In Zwift ERG it feels like I am fighting against something. If that makes sense?
Where as the ERG mode in trainer road feels very fluid. It feels more like riding outside.

I use a wahoo kickr. The newest model.
I don’t understand it…

Have you found the reason since last year?

maybe the power match?

I dont know if zwift has that concept…

  • Yes, Z has their one version of Power Match (trainer resistance set based upon power meter data).

That said, the implementation of that as well as ERG in general may well be different, and lead to the difference in experiences mentioned.

Add Reference:

You can also use ERG mode, which helps you to hold your target wattage during structured workouts. Zwift’s power-matching feature lets it control ERG mode with the data from your power meter.

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I only use zwift on free mode… because i have TR for ERG…

he is probably using the new power match, which is better (at least how i feel it) than the old one.

Yes, PowerMatch 2.0 in use for the TR session is likely, because I think it is the default in all apps now. From what I have read, PM2.0 is far better than the old TR one, that was still regarded as better than Z by many people. So it seems Z may have fallen another step behind with the release of TR PM2.0.

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I just need TR to release an elevation profile mode and I would be set to quit zwift!

(elevation profile where i pick how much virtual elevation and I can ride free mode using that profile)

Not exactly what you are asking for, but have you done any simple Resistance (or Standard if you have Wahoo over BLE) with shifting for control?

That is a ‘dumb’ way to have a “fixed resistance” that you can then dictate. Resistance doesn’t work as well as Standard, based on comments I have read. The Resistance is a very linear feel vs the more progressive Standard that mimics old fluid trainers (that mimicked outside riding).

Both are adjustable for the setting too, so you can fine tune the basic gearing range you want to use. Might be worth a test at least, to see if you can use it like you want.

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I agree, somewhat. :slight_smile:

I can’t speak for Joelrivera, but I would like a SIM mode, where workouts can be setup with gradient and power targets are described (not ERG), and the gradients change with the workout. So, you may have 250W at -0.5% and 250W at 5% and then automatically switch to something else for recovery, etc.

I use a Neo 2T, which unfortunately does not have “Standard” mode in TR. I like the changing gradients, as it’s a nice variation for intervals. “Standard” (progressive) mode is only achievable in SIM mode. :frowning:

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My idea is similar…
is basically a wo where you change the resistance, not necessarily the power…
So maybe mimic a 3% incline resistance but i can set the power i want to ride on…
That way we could input a wo similar to race routes or big climbs on race routes…

I really dont care about zwift as a game. The only reason I use it, its because it mimics roads better than ERG mode on TR.

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The goal is what - to practice shifting?

What you describe is “basically” what I suggested. Just choose Resistance mode instead of ERG. Depending on your FTP and chosen workout, as Resistance setting of 20-40% should get you close.

It’s not perfect, but will allow you to set the power based on your gearing and cadence input. You can load any workout you want, even the race simulation ones if those work, and follow it without the ERG control.

It won’t have the progressive loading like Standard offers, but you may find it’s close enough for your needs. Just try it at least.

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