Zwift ERG & Sudden Low Cadence - screwed?

Triathlon Forum
1

So, finally upgraded from a 2020 Tacx Flux, that both sent bad Watts to Zwift and hence ERG did not work at all.

The new (second hand) Taxc Neo 2T seems to be sending the right watts in “ERG Off” mode and feels much better pedalling.

However, in ERG mode, chugging away happily, at say 260w and 85 RPM, suddenly like en 2-3 seconds, the cadence drops to 30-40 RPM, and I really have to push like 300-320 to “get back to 85 RPM, and slowly the watts comes back to 260w”

I turned “Trainer Difficulty” Off
This can happen in uphill or downhill.

Am I doing something wrong, or is this how ERG works? It screwd up my Z3 intervals yesterday, and I had to go back to manual (ERG off) mode.

Thanks

2

I like to pedal 100 or higher. I swear that Zwift was always trying to power break me down to 95 in erg mode. I have a saris H3 and I asked them, but the reply didn’t seem to understand my question so I don’t know if the way I felt was real.
I switched to trainer road this year, and erg mode works flawlessly. The h3 was known to be the best at erg modes de over tacx, wahoo, and elite. I don’t have much experience with any of those to know. With Trainer road I could achieve a cadence I wanted and not feel like the resistance would try to slow my cadence unless I fought it. With Zwift it always had to be a conscious effort to keep a high cadence.
That’s probably a different problem than yours but I’ve never heard anyone else say anything about this. If you drop your cadence into the 60’s (I’ve never had a slow down to 30-40), erg mode will apply the resistance for the lower speed of the freewheel. If you want to make that freewheel speed go faster again (higher cadence) there is going to be a lag as you pedal up and get hit with a lot of resistance until the trainer adjusts back to the speed change of the freewheel.
Trainers can perform differently at different speeds in their ability to provide a realistic feel. I thought that was my Zwift issue so I had more success in a lower gear (lower freewheel speed). However I switch to trainer road and it doesn’t make a difference in speeds below 25-28 mph. At least it struggles to provide resistance for my zone at a great speed that would go with a high demand for resistance. I have to think it’s a Zwift control thing for this reason that trainer road behaves differently.

3

What do you mean by the cadence dropped? You mean you dropped your cadence? Or there was an error in how the trainer was measuring cadence?

4

What I mean, is that the resistance on the Tacx suddenly forces me down to 30-40 RPM. I can keep pushing 280-300w.

What do you mean by the cadence dropped? You mean you dropped your cadence? Or there was an error in how the trainer was measuring cadence?

5

Ok, just wanted to check. I’d be curious if you were able to dig into the raw data to see what power was being reported. Sounds like it thought you were going too easy so it increased resistance, maybe a temporary dropout of the power data alone? Best, although unpopular, option is to throw out erg mode and ride in manual mode. If you have a power meter, you could try setting that up as your power control on the bike and see if that helps though.

6

Ok, just wanted to check. I’d be curious if you were able to dig into the raw data to see what power was being reported. Sounds like it thought you were going too easy so it increased resistance, **maybe a temporary dropout of the power data alone? **Best, although unpopular, option is to throw out erg mode and ride in manual mode. If you have a power meter, you could try setting that up as your power control on the bike and see if that helps though.

Have you got a pedal/crank power meter, or just the trainer for power? I’d very much agree with the above if the power (or cadence) transmission fails then zwift will ask the trainer to increase the resistance and that’s the issue. That said, after a few seconds it takes erg mode off temporarily, you can spin it up and then when you hold it steady it gradually transitions back to erg. (all this based on my Neo OG - I’ve been a big user of Erg for 5 years now) .

Have you got a link to a session in garmin connect or on strava I can have a look at?

7

Thanks a lot, this help is very appreciated! I do have power meters (P2M and Quarq crank based) on my “outdoor” bikes, roadbike, triathlon bike, and gravel - that I could mount in the HT to test anything, if needed. But the triathlon bike mounted currently in my HT has not power meter.

Here is the .fit file downloaded from TP

The drop in RPM occured in the warm up and maybe (if I recall well in all my heated/sweaty anger) in the first set. This is the proposed training set: OULT training:

Ok, just wanted to check. I’d be curious if you were able to dig into the raw data to see what power was being reported. Sounds like it thought you were going too easy so it increased resistance, **maybe a temporary dropout of the power data alone? **Best, although unpopular, option is to throw out erg mode and ride in manual mode. If you have a power meter, you could try setting that up as your power control on the bike and see if that helps though.

Have you got a pedal/crank power meter, or just the trainer for power? I’d very much agree with the above if the power (or cadence) transmission fails then zwift will ask the trainer to increase the resistance and that’s the issue. That said, after a few seconds it takes erg mode off temporarily, you can spin it up and then when you hold it steady it gradually transitions back to erg. (all this based on my Neo OG - I’ve been a big user of Erg for 5 years now) .

Have you got a link to a session in garmin connect or on strava I can have a look at?

Screenshot 2024-07-12 at 09.24.58.png

8

Here is the moment in the WU where this occured the first time, around minute 9:00 - Power is pink line, cadence is yellow line. TIA

Screenshot 2024-07-12 at 09.37.57.png

9

You’ve got some power drops, and I’m also seeing that the cadence is dubious too - it halves from your normal 80 to 40 around the same time.

Are you connected by bluetooth or by Ant+? What are you running zwift on?

And then the next bit that can help sort it out is if you also record the session on a garmin watch/headunit. So to do that you’ll need to connect the watch/edge via Ant not bluetooth.

I’d strongly suggest the following if you are on a PC.

  1. Use Ant+ not bluetooth
  2. change your home Wifi 2.4g channel to channel 3 (get it away from channels 9-12). Get the ant dongle close to the trainer. I have a 3m usb extension cable and then have the dongle in a little ziplock sitting under the BB (I use Neo and a Quarq powemeter).
10

Got it. Thx

Connected on PC via Bluetooth, as I do not have a dongle. Is that just any Ant+ dongle or any specific you can recommend??

I can try and record a future sesh on my Garmin.

Where does my wifi come into play??

Thanks a lot for this help! T

You’ve got some power drops, and I’m also seeing that the cadence is dubious too - it halves from your normal 80 to 40 around the same time.

Are you connected by bluetooth or by Ant+? What are you running zwift on?

And then the next bit that can help sort it out is if you also record the session on a garmin watch/headunit. So to do that you’ll need to connect the watch/edge via Ant not bluetooth.

I’d strongly suggest the following if you are on a PC.

  1. Use Ant+ not bluetooth
  2. change your home Wifi 2.4g channel to channel 3 (get it away from channels 9-12). Get the ant dongle close to the trainer. I have a 3m usb extension cable and then have the dongle in a little ziplock sitting under the BB (I use Neo and a Quarq powemeter).
11

What I mean, is that the resistance on the Tacx suddenly forces me down to 30-40 RPM. I can keep pushing 280-300w.

What do you mean by the cadence dropped? You mean you dropped your cadence? Or there was an error in how the trainer was measuring cadence?

What you’re describing sounds a lot like what they call the erg spiral of death.

Erg mode helps keep a constant power by constantly adapting the resistance to your cadence. If you lower your cadence, it increases resistance, if you increase your cadence it reduces resistance.
The issue arises if you’re reducing cadence too quickly and/or the power target is too challenging.

It also takes a little paying attention. If, for instance, you’re doing a workout while watching TV, you might easily find yourself grinding at very low cadence.

Shifting gears can also cause issues. It can be very tempting and instinctive to switch gears during a workout but erg mode will keep applying its logic.

Is it possible that you’re using power targets that are beyond what you can actually hold (even if just a little challenging)? Presumably if your previous trainer wasn’t accurate, you’re trying to hold power targets that aren’t feasible for you now that you have a more accurate trainer.

In general, challenging workouts are easier to complete without erg mode.

By the way, trainer difficulty and inclines have no impact on erg mode.

Also, the way the trainer works in erg mode is that the app sends a power target to the trainer and the trainer does its magic. Erg mode functionality is relatively independent of the connection to the app. If the app suddenly loses connection to the trainer, the trainer simply would stay at the last power target received.

Does the above help or do you think it’s an actual issue with your trainer?

12

In general, challenging workouts are easier to complete without erg mode.

This is the best thought in this entire thread. While IDK if they are easier or not to complete in ERG, ERG mode is not = to outside riding when it comes to power application.

I do love when my athletes competitors do all their workouts in erg.

13

So you recommend not using ERG?? I can live with that.
For what I am doing indoor, which is between 260-350w (Z3 to mid Z5), it´s not a lot of shifting required really.

I have big mountains just in my backyard if I really need to hurt myself :slight_smile:

In general, challenging workouts are easier to complete without erg mode.

This is the best thought in this entire thread. While IDK if they are easier or not to complete in ERG, ERG mode is not = to outside riding when it comes to power application.

I do love when my athletes competitors do all their workouts in erg.

14

Marco - thanks. I read about the Spiral of Death. But doubt this is the case here. I literally just started warming up and BOOM, it was like hitting a 20%+ wall.

15

I’d definitely recommend not using erg. I’ve always felt there’s something additionally beneficial from being forced to stay on top of your gearing to do the intervals yourself. Great practice also for learning how to stay in touch with yourself and better use RPE as well.

16

So you recommend not using ERG?? I can live with that.

I wouldn’t say I don’t ever say don’t use erg, yet I’ve never written a workout that was erg specific or told my athletes they needed to ride in erg

ERG mode is not = to outside riding when it comes to power application or even cadence.

If I have an athlete do efforts, or just ride, then look at their power it’s obvious which workout was erg and which was not. If I compare a power file erg to non erg and then both an erg and a non erg to an outside power file, the outside one looks a lot different than the erg one does

17

Got it. Thx

Connected on PC via Bluetooth, as I do not have a dongle. Is that just any Ant+ dongle or any specific you can recommend??

I can try and record a future sesh on my Garmin.

Where does my wifi come into play??

ANT+ and bluetooth both use frequencies within the same range as 2.4G wifi. So if your router is close to where you train then it can swamp the signals. So changing the wifi channel to be at the other end of the spectrum to the ANT/Bluetooth is a simple change with no downside.

Any ANT+ dongle will work. I’ve one garmin and one non garmin and there’s no difference in reception. One is a lot smaller than the other but I can’t remember which is which to be fair. Obviously the no-brand one was a fifth of the price of the Garmin one.

18

In general, challenging workouts are easier to complete without erg mode.

This is the best thought in this entire thread. While IDK if they are easier or not to complete in ERG, ERG mode is not = to outside riding when it comes to power application.

I do love when my athletes competitors** do all their workouts** in erg.

Interesting posts and I wouldn’t even dare to argue with either of you noting your experience. But the bit I highlighted is the key. Easy for people to read the post and miss that bit and think it’s better to never do erg mode. Perhaps it is athlete dependent, and also on how many sessions you are doing a week, what the mix is. I 100% agree that there is a massive difference in feel between doing intervals outside, inside ‘free’ and inside on erg.

But I think of it a bit like swim sets. It’s a lot easier when you are not leading the lane, and are just pushing yourself to stay on the feet as opposed to swimming on your own. But squad swims have been hugely beneficial at keeping me motivated to swim 3 times a week and push harder.

The part I’d ask is if the interval power levels are designed optimally for the athlete, then erg mode would surely lead to them working out with a higher level of compliance with the intended set. Erg sets shouldn’t replace the training to hold target power for the duration of the race. But in terms of maximising the benefit for the time (and energy spent) then they are valuable to me. I wonder if it depends on how you’re balancing life. I’m not a full time athlete. I have a job and so my ‘cognitive battery’ is drained by that. So in the week, I get up 4:45am to do my zwifting before work. And in that time then being able to decouple the brain is handy. Same for 45min recovery rides. Conversely, on a weekend then I either ride the local club groupie in the off season, or go outside and do my ride to any target power guide from my coach using the average lap function - not even a programmed workout. That said, I’ve been cycling 45 years and having ridden with plenty of other road and triathletes then seem to have a much better natural awareness of cadence and gearing.

19

Got it. Thx

Connected on PC via Bluetooth, as I do not have a dongle. Is that just any Ant+ dongle or any specific you can recommend??

I can try and record a future sesh on my Garmin.

Where does my wifi come into play??

ANT+ and bluetooth both use frequencies within the same range as 2.4G wifi. So if your router is close to where you train then it can swamp the signals. So changing the wifi channel to be at the other end of the spectrum to the ANT/Bluetooth is a simple change with no downside.

Any ANT+ dongle will work. I’ve one garmin and one non garmin and there’s no difference in reception. One is a lot smaller than the other but I can’t remember which is which to be fair. Obviously the no-brand one was a fifth of the price of the Garmin one.

Wifi and bluetooth can both work in the 2400-2483 range, with wifi occupying a 22Mhz block of that. Bluetooth on the other hand can hop across those frequencies. So I don’t think you’ll see much benefit to changing wifi frequency, although that might depend on if you have neighbors with additional routers near you.

What I recommend is to check the network settings on the device you’re using with Zwift - your PC, AppleTV, or whatever. Make sure it is connected on the 5ghz band. That’ll ensure bluetooth / ANT+ have the 2.4ghz band mostly to themselves. Also make sure your phone is connected to the router on 5ghz - this is particularly important if you’re using the Zwift Companion app.

A couple more tips for the OP: if you’re not using the Zwift Companion app, give that a try or vice-versa.
And finally: if you have recently used the Tacx app on your phone, it will interfere with Zwift. So make sure you’ve closed / killed that, or restarted your phone so that app is completely shut down.

20

Lots of great input here - much appreciated! I will get an Ant+ dongle and play around with my wifi, etc.

Will chime in here, if/when I learn more!