Inertia in Erg mode - is slower always better?

I’ve recently started using a Kickr Core, a big upgrade from a basic fluid trainer.

I understand that for a given power using a faster gear spins the fly wheel faster and so the effort “feels” easier.

I have watched the video about muscle recruitment and how that changes with flywheel speed, regardless of power. The suggestion there is to try and replicate the event you are training for.

My question is, wouldn’t it be better just to leave the bike in a lower gear and suffer it, assuming I can still manage the prescribed training?


The idea behind ‘replicate your event’ is that if you’re turning over a big gear (generally road riding) the high inertia of a bigger gear better simulates your outside riding.

If you’re turning over a little gear in your events (short punchy climbs, mountain biking) then the lower inertia better simulates the constant accelerations.

It isn’t necessarily easier or harder - it’s just different - they both work your muscles slightly differently.

All of that said, I’ve used both extensively and haven’t really felt a huge difference in my outside performance (spent an entire winter on the little ring, then the next winter on the big ring) so I’m not sure how much difference it really makes

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Maybe I’m crazy but i feel like erg mode reacts faster when im in the little gear so i leave it there.

My outdoor rides are generally flat with some rollers, I’m in in the big ring about 85% of the time. Indoors I test and do workouts in the little ring exclusively. I find that the lower inertia means the trainer responds faster to changes in wattage demands. I’m convinced that training in the big ring would make the workouts feel easier and there are plenty of anecdotes and videos to support that claim, but I prefer the responsiveness. In tough workouts, I like to believe it’s making me stronger. All the indoor gains I’ve made have transferred to outdoors and I don’t think I’ve suffered for not training in the gearing that I typically do outdoor work in.

Not crazy at all, that effect is very real.

The reason is that the slower flywheel speed (and related inertia) are easier for the resistance unit to control vs a higher gear and faster flywheel (and the greater inertia).