Trainer power meter reading low on trainer road?

Is there anything about the trainer road app that would affect my trainer’s resistance in ERG mode? (ie make it harder at a given intended wattage)

Signed up today and did the ramp test today. Got to 294 watts. While I was doing it it just felt super hard for the watts, and my trainers (tacx neo) was reading lower than my power meter on my bike (just by eye, wasn’t recording my power meter).

I did this test a couple of times on zwift 8 weeks back, when I’m certain I was less fit, and completed 340, and 360 (but stood up for that one).

I tried the sufferfest version to check afterwards and got to 320 but was pretty knackered from the first attempt so probably would have finished 340 fresh. Also recorded this one my bikes power meter and last minute was within a few watts.

Anyway, any thoughts appreciated? trainer taking a while to warm up maybe?

  • First consideration is gearing. Are you using the same gearing in ERG in TR as you were in Z & SUF?
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Hello, thanks for reply. Yes I was. Big ring and not sure which cog but one with the chain pretty much straight.

Out of interest, can this make quite a difference? what gearing tends to make your watts higher/lower?

I would expect that using the big chainring will spin the flywheel faster and make it easier. I always use the small chainring in erg mode. It makes it more realistic.

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Opinions vary, but try pedalling at a single ERG level in max and min gearing, and you will likely feel that one is “easier” than the other.

Higher flywheel speed has also been shown to give more variation in trainer power data vs power meter data. Most seem to report more consistent data between devices at the small ring.

Big ring vs small ring in ERG is largely a preference option.

Faster flywheel:

  • usually closer to feeling like higher inertia road riding.
  • may be a bit louder with the higher drivetrain speed.
  • leads to more visible power graph variation as the faster flywheel makes Resistance adjustments tougher on the trainer.

Slower flywheel:

  • Pretty much the opposite of all above.
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