Help me understand

Hi guys,
I’m using Trainer Road for a week now, but there is something I can’t understand. I have Tacx iGenius smart trainer and my FTP is 231 watts.
Today I did Avalanche Spire workout, I started with 34 in front and 20 on the cassette, cadence between 85 and 95 … I was ready to give up in the middle of the workout. It was too hard, almost impossible for me to reach the target.
Then I switch the gears to 50 in front and 13 on the cassette which is supposed to be harder, but not I finished the workout without any problems, even the average cadence in this second part was higher (100-110 rpm). It was easy for me in this second part.

What I miss or what is the right thing to do?
P.S.: I’m on ERG mode.

I use a Tacx Vortex and find I can handle workouts better with large chain ring and middle cassette. Small chainring feels like I’m riding through mud.

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While it’s about a different trainer, the concept here is the same:

It’s all about inertia. Watching that video should clear it all up.

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Thank you for the video it’s really useful. I understand the idea behind, but still can’t answer myself where is the truth.
Is the inertia something bad or good? Am I getting the most from the workout if I’m cycling using inertia or not?
My understanding is that in the end, the important things are the watts and to complete the workout reaching the targets but I can do this easier using the inertia or trying to do the same without inertia and to give up in the middle…

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Different people will tell you different things–some people seem to think that low inertia makes you work harder, which should theoretically provide “better” results.

I don’t think it’s quite that simple, because with lower inertia you’re starting to work different muscle groups.

At the end of the day, I’m in the “high inertia” group. I ride a 1x with a 50t chainring, so I generally use 50x21 or so for most rides. I’ll go a little lighter on endurance or recovery stuff.

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And based on that, we have a length thread diving deeper into the topic.

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Short answer is that we simply don’t know. I think that people should play with each option and choose what they like best.

The differences are likely minimal in the grand scheme, and akin to the “marginal gains” realm that is extremely hard to pin down.

Without some very structured and measured testing, we will not know for sure if it makes any difference, or how much in the case that it does matter.

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That’s it. I’m changing my gearing.

I train in ERG mode and am in the small chain-ring and in the 4th cog. I want something to feel easy (or easier) for a change. I’m going back to the big ring.

I don’t care if it’s real or not. I want the placebo :smile:


Check out the thread linked to above about big ring vs small ring.

Separately, I actually think that some trainers (and power meters) measure power differently between big gear vs small gear. I’ve seen enough people talk about pretty noticeable differences in how easy a workout feels between big gear vs small gear. And I suspect it’s not all due to inertia.

I think it’s related to how power meters can sometimes measure power differently between oval vs round chain rings.

In mathematical terms, it comes down to the algorithm used to measure and integrate the multiple of power and angular velocity over the pedal stroke.

I have no proof on this, just suspicion, so I’ll stop there :thinking:

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