Power at Low Cadences

Hello Everyone,
I wanted to turn to the knowledge of the community to see if anyone can help me understand something I saw in today’s workout.

I did Carpathian + 2 this morning and really struggled through it, so on the last interval of over and under I resorted to doing several 3 minutes out the saddle pedalling.

I was on a smart trainer (Tax Neo) and using ERG mode so I thought the power would closely follow the target but when I was riding and, more evidently, when I analyzed the workout I saw that actually the power I was producing was way under the target:

Why is this the case given I was in ERG mode? Shouldn’t have the trainer just adjusted the resistance? Did this level mean my trainer didn’t have the capacity to produce that resistance (seems unlikely)? Is this a measurement error (felt hard, but also seems unlikely)?

Thanks for the help in advance!

Tobias

Trainers seem to react slower at slower cadence, I can’t really explain why but mine does too (though not this far off). Did you feel any flywheel slippage while doing these intervals? The Neo I tried was awful with this and I’m sure it would impact readings

Not really! I didn’t feel any and the power felt the same than in the other intervals (but I was considerably more tired so maybe they were).

I’m considering sending the workout picture to Tacx.

What gearing were you using for the seat and then standing efforts?

How “smooth” are you at standing like this? Do you have the “chain gap issue” where you get the slack and tap of the freewheel, or are you keeping good tension on the chain around the circle?

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Hey Chad,
Thanks a lot for the reply.

Given I was riding in ERG mode the gearing didn’t change throughout the workout and I’m pretty smooth when standing so I never notices any loss in tension. I will check this on my next ride, I haven’t changed the chain in a while to be honest.

I also sent an e-mail to Tacx.

Tobias

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Ok, but what was the gearing used?

34 / 22, does it make a difference in ERG mode?

Just want to learn.

Thanks!

I would shift when you stand and sit. That would keep the trainer flywheel speed more consistent and require less adjustments from the trainer when in erg mode. If you don’t shift you are going to see big swings in flywheel speed / power as you change positions and some lag with the trainer adjusting resistance. I have seen as well as you are now that perception of power / RPE when changing positions between sitting and standing does not always match reality. The power looks on target during the interval when you move back to sitting.

It takes a little while for the trainer to recognize a power drop and adjust cadence, and on the sawtooth intervals like that it will always be chasing the target power. I suspect if it was flat power over/unders the power would have more closely matched the target. But it does look a little laggy in responding.

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Gearing can matter, especially for some trainers.

The Neo is a different beast compared to others. The way it generates resistance may be impacted by gearing in unique ways.

Most trainers perform faster in a low gear like you use. The lower wheel speed allows the resistance unit to keep a good hold on things.

But since the Neo uses a virtual flywheel, it is not a guarantee that anything know about other trainers applies here.

I’m honestly surprised that it fell short on those intervals. And I don’t have a good idea why at the moment.

You may have better luck contacting Tacx Faqx (FB and web). Drew is the most knowledgeable guy outside of Tacx when it comes to the Neo.

Ditto, I recommend shifting in ERG and wrote an article on the how and why.

https://zwiftinsider.com/shift-during-erg-workouts/#:~:text=Get%20into%20an%20interval%20at,or%20use%20the%20small%20chainring.&text=Perform%20the%20desired%20standing%20effort,just%20like%20normal%20ERG%20riding.

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Never seen this on my Neo in erg. Just wanted to check that you only have the trainer paired with EITHER bluetooth OR ant+ and NOT BOTH.

I got weird behavior like this because of that

Thanks a lot @mcneese.chad, very useful and I’ll read the article!

@ryanppax, I think you might have hit the nail’s head. I was indeed running TrainerRoad through Bluetooth and Zwift through Ant+ (not controlling though). Was this the way you were running it when you experienced the weird behavior?

Have a good start of the week!

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One possibility is that the low cadence efforts on that gearing put the Neo into a situation where it can’t generate the necessary resistance at the “flywheel”, and it feels like slippage.

A couple of ways to test this:

  1. Ride at 150 watts at the same low cadence
  2. Ride at 300 watts at the same low cadence in a bigger/harder gear Eg big ring, lower half of the cassette.

If the Neo behaves normally in these situations, that points to some form of slippage. And if this is the case, seems like a defect in the trainer - as the power/cadence/gearing you’re riding at don’t look that extreme.

I’d be a little surprised if it’s the BLE/ANT thing, as the trainer was working fine when pedaling under “normal” cadence. But worth checking to confirm.

Good luck resolving things.

Both mine were paired in TR

I have a Neo and have never seen anything like this and I don’t typically shift when I stand.

Here you can see what happened when I stood during Hunter yesterday.

Elite Direto (ERG with low gearing) and I usually see a significant dip in power when initially when I get out of the saddle. It can take up to 10-20 seconds for ERG to bring the resistance back up to target. This is counterbalanced by a spike in power when i return to the saddle and increase cadence.

Thanks all for the answers.

@DaveWh I will try that this week and see what happens.

@russell.r.sage that exactly what I was expecting to see.

@biberg in my case it never recovered as you can see.

Have a good week!

Tobias

What gear are you in? If you’re in a significantly harder gearing then the trainer doesn’t need to make up a deficit that is beyond its limit.

Yes, the gearing was 34 / 22, so probably better to shift.

I think the point is, the Neo isn’t really limited. I could be wrong, but my understanding is it’s high and low ends do not require any shifting avoid ceilings or floors in a normal cassette range. I ride in the same gearing from my easiest recovery in the 70’s to whereever I top out on, nearly 1000.