Power through smart trainer or power meter?

I like to ride in Zwift while doing my TR workouts. Today I tried an experiment: I connected my left-side crank power meter (4iii Precision) to Zwift and used my Elite Suito smart trainer power meter for TR. I was surprised to see that the 4iii power meter was consistently 10-15 watts higher.

I then set up TR to run using the Powermatch feature and while the difference was less, the workout was much easier than when I was doing it with just the Suito power meter. For what it is worth, I was in ERG mode.

Any idea which is more accurate, and which I should be using?

Also, sorry if there are already threads discussing this exact issue but I couldn’t find any recent ones and I think TR recently upgraded their Powermatch feature.

PS: yes, I calibrated both power meters before the workout.

  • Not a chance we can answer that without at least a 3rd power meter in the mix.
  • Depends on your goals. If you are using the power meter for outside rides and races, using that same “tape measure” via the PowerMatch feature is best. This makes sure you use the same device in all your use cases.
  • PowerMatch changed, but it was well over a year ago IIRC. Regardless of the improvements made, it does not significantly change the core issue here… power devices often report different data.
  • Keep in mind, if all you are doing is “eye balling” the delta by quickly looking between two screens, this is far from conclusive. It is impacted by the smoothing setting in place in each app at the very least. Even if those are “matched”, the sampling and data presentation between them is not guaranteed to be “comparable”.

  • If you really want to head down the comparison rabbit hole, you need to take more steps.

  • With respect to the feeling you have, that is a direct result of changing from “tape measure 1” to “tape measure 2” within TR. You effectively shifted the data point that sets the resistance, and as such, will alter your experience. It’s totally expected based on the apparent delta from your rough comparison.

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Thanks for the reply. Yes, I do race and use power outside, so maybe I will stay with Powermatch. I am just surprised by how much easier it was. I have always felt I could hit higher power numbers outside, although I know there are other factors for that as well.

Not sure I am ready for the rabbit hole though. :slight_smile:

Firstly, because of drivetrain losses, and the 4iiii measuring “upstream” in the drivetrain, you can expect it to read slightly (1-2%) higher than the Suito, even if both are 100% accurate.

Secondly, potential L/R imbalances in your power output mean the 4iiii (which doubles the left leg) may not be reporting the same as the Suito (total output) , again with both PM’s measuring 100% accurate. Power imbalances are the more likely cause of the difference in reported power.

If you are doing a mix of inside and outside workouts, you may want to use powermatch for consistency,

But if all your structured rides are inside, and outside rides are just free rides, then you may want to use the Suito as your power source.

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That’s a good point. I race and ride outside with power, but I do not train outside. I strictly train inside. So maybe I am better off sticking with the Suito. And I don’t worry too much about power during my races. I just ride hard and then admire the data after the race. I don’t use power data during the race to inform my strategy.

  • Then keep PowerMatch in place with both your power meter and smart trainer connected in TR and move forward.

One key note though, in a case like this where you are effectively switching between device A and B for power data, you should consider how and when you got the data for your current FTP. If you tested and got results based upon the trainer, and then swap to data from a power meter (that is different more often than not), your training may well be “shifted” one way or the other.

As such, the prevailing recommendation is to redo your FTP test anytime you make a notable change in power data measurement and/or trainer device.

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Not much chance your left and right legs are putting out an equal amount of force. In my case my right leg usually puts out 2% more, so I’d be shafting myself out of some watts with a left sided power meter. I’d stick with the trainer.

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I stopped doing ftp tests and just rely on the AI detection feature, which I think also factors my outdoor rides, right?

IMHO there are no downsides to using PowerMatch. If you have 1 bike, it means you have 1 power meter and simplifies any analysis or estimates for pacing outside efforts. All upside, no downside.

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Yes, AIFTPD factors in all cycling workouts & rides imported into the TR calendar.

Ditto. I get the notable aspect that the pedals are single-sided, but if that is used when reviewing outside rides (workouts or not), it makes the most sense to use the same tape measure in all cases.

Introducing an X-factor of a different device (smart trainer), just because it is “better” in the light of providing real, total power… is not enough justification to include what is already seen as a delta in the data. To a degree it might boil down to:

  • Is “total power data” with a delta used part time better than “1/2 power data doubled” the same all the time?

Both are “flawed” in essence, so I’d chose the one that is a consistent flaw inside & outside.

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And this would be yet another reason to use Powermatch, would you agree?

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Yeah, that’s why it’s what I recommended it in my first reply above :stuck_out_tongue:

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Gotcha! Thanks!

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