“The resistance is there. So I’m not sure what Zwift mean that it’s only a feeling. It isn’t make believe resistance- so what does that mean?”
I think your confusion is understandable, because I wondered about all of this stuff and what it meant before I got a smart trainer and finally ‘felt it’ for myself.
I’ll probably do an awful job trying to explain too, but here goes:
From the link above, there’s this bit with ** emphasis added by me…
" It is important to understand that lowering or raising Trainer Difficulty does not change the power needed to get up the hill. You still have to put out the same **cumulative watts** to move the same distance as before… you’ll just be doing it in a different gear."
I keep my trainer difficulty set at 100%, and as resistance ramps up on a climb - it becomes increasingly difficult to turn the cranks. It takes more power to sustain a given cadence in a given gear as the gradient increases, and that increase in power is measured by my trainer and reflected in the number of watts displayed by Zwift.
If I downshift *and maintain the same cadence* while the slope remains constant, it is easier to pedal. I am, therefore, putting out fewer watts per pedal stroke - so my speed will decrease compared to what it was in the higher gear, and I have to turn the cranks through more revolutions to go the same distance. My speed up the hill is lower and I spend more time on it turning the cranks at a lower effective resistance level BUT the **cumulative** amount of work it takes to from the bottom to the top is the same - regardless of your gear choice.
Essentially, the Trainer Difficulty setting has the same effect. Dropping the difficulty doesn’t change the amount of work you need to do, it just offers you a (potentially) less difficult way to get that work done.
Pick an easy gear. Climb a 10% grade at whatever steady cadence you can sustain @ 100% difficulty and look at the Watts and speed displayed.
Keep the same gear. Climb the same 10% grade again (at the same cadence as above) at 50% difficulty. Look at the Watts and Speed.
Your power (and, in turn, your speed in the game) will be lower @ 50% difficulty if everything else is equal. But - as above, the total work done will be the same going from point A to point B - it’s just spread over more time.
If you want to *maintain the same speed* in both cases, then @ 50% difficulty, you have to choose a higher gear and/or cadence to get your power to match what it was going up at 100% difficulty (which you may in fact be able to do, because effective gradient is not as steep - but because you’re now turning a bigger gear and/or pedaling faster? It’s not going to feel any different effort-wise vs. 100% difficulty - because you’re doing the same work in the same amount of time!
The only good reason to use anything other than 100% (strictly IMO) is if you want to climb hills that are either a) *significantly* steeper than the max %grade your trainer is capable of simulating or b) you don’t have suitably low gearing to enable you to sustain a high enough cadence to get up the mountain w/o grinding painfully to a halt.
I hope that helps?