Trainer difficulty on Zwift // What is it? What does it do? // What is the best difficulty on zwift?

Hey y'all!
We chat about trainer difficulty and why you would increase or decrease it, what it will effect and how it will change your experience in Zwift.
Its a hot debate with people getting called out for lowering it down, but it can be a useful tool when you understand exactly what it does.
What are your experiences with trainer difficulty? What settings do you run?

[@kaiyu4001]

For most of us, because of all the other fudge factors, trainer difficulty is just like using a different cassette. It isn't the exact same thing. The distinction is screechy/niggling, but it goes like this:
Power = Force x Velocity
If you take Force and break it down into aero and climbing components (just for simplicity), then:
Power = (aeroForce + climbForce) x Velocity
A cassette swap acts on aeroForce + climbForce.
Trainer difficulty only affects grade, therefore, it only acts on climbForce.
Because cassette swap and trainer difficulty usually move in the same direction (their effects are coextensive), trainer difficulty adjustment looks like a cassette swap to normal people.
When they move in the same direction, it is like a cassette swap (and that's how many people use the setting).
But because they act on different variables, it's not a perfect match, and so it's not a cassette swap. There can also be some fun mathematical oddities, like when you lower the climbForce requirement even though you can comfortably output the power. (It can lead to higher velocity and thereby higher aeroForce.)
All of that said, I'm comfortable explaining it and thinking about it as a virtual cassette swap. It's how most of us use it. The distinction doesn't matter.

[@Scott221]

Science! Love it Kai!
Yep this is another factor. But the most basic explanation of trainer difficulty is how it will affect your training and what you will experience on the bike.
When you get in the real world, you can’t virtually swap a cassette, so why do it when you’re training.

[@kaiyu4001]

@@Scott221
I think the “why?” just boils down to what we each individually use Zwift for.
For example, the issue is completely moot when I’m on a training plan since I’m in ERG mode anyhow.
Generally though, my trainer bike is geared differently than my road bike.
And during the winter, I might just be looking for Z1/Z2 rides, but I can only ride Tempus Fugit so many times before my eyes start to bleed. So It’s nice to be able to change the scenery without having to actually climb a mountain.

[@Scott221]

I know what you mean about tempus fugit :) I think we’re all the same! Absolutely, the why is the most important thing - as-long as you’re having fun and being consistent, you’re half way there.

[@razerbaz]

Not sure if there is something wrong with my trainer its the same as yours, but if i move the slider to 100 % i cant move the pedals ,i changed to a 11/28 but it still wont react like yours.

[@inscribedpizza]

To make it more understandable, could you demonstrate how are in game speed and power output affected if you keep a given gear and cadence (erg off) on a constant slope at trainer difficulty 0%, 50% and 100%?

[@Scott221]

Hi :) Thanks for the comment.
To answer your question, if you kept a constant RPM of 100 and stayed in the same gear - as you increased the difficulty, your watts would increase.
This is due to the torque increasing on the trainer, therefore the cadence and gears you have selected will output higher power, as you are working against a harder force.
I hope this makes sense?

[@inscribedpizza]

@@Scott221 thanks for the explanation, so it simulate to have longer (increasing difficulty) or shorter (decreasing difficulty) gears? I'm not sure what's the effect of training difficulty on my setup since I don't have an erg capable trainer 🤔

[@Scott221]

@@inscribedpizza If you cycle up a 10% incline with the trainer difficulty set to 50%, you will feel a 5% incline through the pedals. If you set it to 0, you feel no incline through the pedals.

[@donwinston]

I still don't understand why Zwift does this. If you want a "real" experience why would you want anything but 100%? I always have mine set to 100%. Didn't know this doesn't effect the downhills.