Bug: ERG mode has intermittent drops in resistance and reported power (Wahoo Kickr)

I don’t know if its normal/how others ride, but I do change gears occasionally even when in ERG mode. I don’t know if its in my head but it “feels” very different in different gears. I prefer the “feel” of the big ring at the front, and then I kind of move around on the cassette occasionally but clustered around the middle (so with a clean chain line on my 2x11 setup).

That’s how I rode today (almost) but the feeling was very different and not as pleasant. Very hard to describe the difference but felt like I was using more cardio and less “legs” even though power output was the same. I can’t think of any reason why that would actually be true but I prefer the feel of the big ring and it feels like it maybe needs more torque to affect small cadence changes? I don’t know.

That’s interesting, yes it does feel like an overshoot/undershoot issue relating to the flywheel perhaps - I wonder if essentially (despite my relatively weeny power numbers - I’m not power monster like many out there!) if I’m exceeding the flywheel’s ability to damp the inertia in time or something and cause these spurious readings?

It really feels like something that should be trivial to solve - in my head, its as simple as if you’re in ERG mode at a set power, then that is the power the trainer should report - you’re either still pedalling (and hence at the power required) or the cadence has dropped to 0, and you quit the interval. It almost seems unnecessary in ERG mode to do anything else in terms of power reporting.

I only mentioned normal as you had said it further up.

It is very bad practise to shift gears when in erg mode, pick one and stay in it. It is like opening the window when using air conditioning!

I do know what you mean, i think it is down to how much of the chain you pull over the ring at the front, you kind of pull the chain up and over the big ring where as it is more just being pulled down on the small ring. This is just my guess and is likely very wrong btw!

For what it is worth i prefer big ring when in erg mode but it does have a much worse experience overall so I stick to small ring and biggish cog at the back. It is even more noticable if you use a seperate power meter (which i do) that the trainer is trying to over compensate to the changes in your pedal stroke.

GP Lama does tests on trainers at different flywheel speeds which highlights why smaller gears are better for most trainers.

Just to clarify, the issue doesn’t occur when I change gears, and I don’t change gears often, only occsionally when standing up out of saddle to deliberately increase resistance briefly - its unrelated to this bug and a red herring, wish I hadn’t mentioned it now :smiley:

No you do a better job of describing it than me, it just “feels” better and more natural/like riding outside. Its the same reason that I didn’t like the Tacx Neo that I tried I think and preferred the Kickr - that doesn’t use a flywheel at all (to my understanding) but just pure electro-magnetic resistance (I think?). To me it just felt like being in the small ring on the Kickr, only worse, and not at all natural.

That’s a interesting point, if I used pedal-based power to read power, but used the Kickr as the “controllable” device, would the ERG mode in big ring work without the dropouts then do you think?? Its a hell of an expensive way around the issue, but I’m wondering if that would be one option for solving the issue to bear in mind, even if its not financially viable for me immediately! :sweat_smile:

It depends what is causing your problem - if it is caused by a big and sudden change in the power you’re putting out and the trainer over compensating or struggling to hold the power to the target it will likely make it worse as the pedals would be more reactive to spike in power…

Have you tried using the big ring and a bigger cog at the back, when i had a tacx flow i found erg mode would be fine in big ring and then the 2nd or 3rd biggest cog at the back. Cross chaining isn’t ideal but was ok for erg mode (at least i found it was)

I did briefly try that but the cross-chaining was pretty severe on my setup in that configuration to the point that I wasn’t comfortable riding like that, the cog (or something) was noticeably louder indicating (I would think) that something wasn’t happy and i’d cause premature wear so not a long term solution I think.

I think i saw something on GCN about how cross chaining doesn’t really increase wear on parts. I may have dreamed that though!

It may have been rubbing your front mech. properly indexed gears should be able to use all gears without too much excess noise.

Cross-chaining was more of an issue with old-fashioned chains with bushings which were a lot less flexible. This can be easily demonstrated by taking a single-speed chain (which still use the traditional construction) and a modern 10/11/12-speed chain and seeing how easily the latter bends sideways compared to the former.

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It has taken a while but Wahoo have confirmed that this is a niche/edge-case bug in their trainers and how they use “chain tension” to try and calculate both power and cadence. However, they also confirmed that they’ve got no development resource to fix it, due to it being a relatively rare issue.

So somewhat surprisingly/generously they’ve offered to simply refund my trainer in full. Which leaves me with a bit of a quandary - I need a new turbo trainer, and ideally one that won’t be subject to a similar issue. Does anyone have any guidance on this? I believe I’m correct in thinking that the Tacx Neo has no flywheel and uses purely electromagnetic resistance, is that right? And if so, would that mean that it should not be susceptible to this issue in the same way since there is no flywheel to “get ahead” of the pedal/crank cadence?

I have no real upper limit to budget but I do want a turbo trainer and not a dedicated trainer bike, so I’m open to suggestions on what trainer I should look at if my main requirement is riding in ERG mode (controllable) in big ring without issue.

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I’m going to try one more thing before I give up on the Wahoo Kickr - I’m going to try and get hold of some power meter pedals, and use these as the power source, but keep the Kickr paired as the “controllable” device. I’m hoping that since the power meter pedals shouldn’t have the odd drops in power that the Kickr suffers from (due to apparent issue with detecting input via “chain tension”) that this combination should work. I’ll feed back and update this thread either way since it can help anyone else affected now or in future.

Cross-linking for reference to another thread I just found from a user having the exact same issue, so I am not alone in experiencing this!

Just an update on this to say that my plan (using power meter pedals as the power source and the Kickr as the “controllable source”) did not work unfortunately.

When using this setup, it allowed me to set it up this way and the devices showed correctly in the pairing screen, but the Kickr simply wouldn’t hold a steady power in ERG mode at all. Perhaps that’s by design.

You can see here the problem - this was all in ERG mode, but the section right of the vertial line was when I gave up and switched the power source back to the Kickr.

So unfortunately that’s me out of ideas on this one. It looks like I simply need to accept the issue, or accept Wahoo’s offer of a full refund and switch to a different product such as Tacx Neo.

Unless anything changes, I won’t update this ticket again but hopefully it will be of some use to anyone else searching for same issue in the future…

I use pedals as power source in erg mode - it works but some trainers really need you to be in the smaller gears and for you to pedal quite steadily. if you’re someone who moves around a lot on the pedals or has a slightly erratic pedal stroke with inconsistent power it probably won’t be ideal for you.

I have used separate power for Elite Zumo, Elite Drivo, Tacx Flow, Tacx Flux and Tacx flux 2 all of which worked well with power meter pedals as power source and the trainer as controllable (obviously!)

maybe give it another go - it can take a second or two to stabalise and the graph will not look like the wahoo did with smoothing on - but then that is the trainer lying anyway!

I see that Wahoo has released a new firmware for their latest Kickr 6 only, and it addresses random drops of resistance in SIM mode however, not ERG mode.

  • Fixed: Loss of resistance sub-3 mph / 4.8 kmh in SIM mode

I also started to get these random drops in resistance in SIM mode recently, usually on some sort of sustained climb (but not under 3 mph). I never had this issue with my Kickr Core, but when I did a warranty replacement this past summer they sent me a Kickr 18 instead of a Core, and now every once in a while I get these random drops.

Thanks yes my issue seems to be restricted to ERG mode (or at least that’s where I spot it, the “noise” in Slope/sim mode would make it a lot harder to spot) and definitely doesn’t only occur at super low speeds, it often occurs when riding at a (virtual) 35-40km/h

Probably my final update on this - I have abandoned the Wahoo Kickr ecosystem after over a year of attempting to get this situation resolved. I now have a new trainer (Saris H3) and ERG mode… works perfectly. ZERO dropouts. So it 100% is not an issue to do with either Zwift or Bluetooth signal or anything else, its simply a hardware fault with the Kickr. Since I have had two Kickrs and BOTH have had this issue, I am pursuing a warranty claim and return of both units

I would advise anyone else who plans to make use of ERG mode to avoid Wahoo Kickrs. Theyre great trainers in every single other respect, but have a serious flaw in ERG implementation and have stated they will not (or cannot) fix, which indicates to me it is a fundamental hardware flaw and not something that a software/firmware update could ever resolve.

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