For Smart Trainer uses, the settings menu in Zwift includes a slider called “Trainer Difficulty.” This is what Zwift officially says about it:
Trainer Difficulty allows you to scale the feel of the climbs from 0 to 100%. This won’t make you any faster or slower as it still takes the same amount of power (watts) to move your avatar (by default, Zwift treats the gradient as half of the true grade).
By default, this is set at 50%, which is why Zwift says it “treats the gradient as half of the true grade.” So when you hit a 10% grade in Zwift, it should feel like a 5% grade in the real world. Why does Zwift default to this? I’m not completely sure, but my guess is it has a lot to do with certain trainers (like the Tacx Vortex Smart) only supporting certain maximum grades. (The Vortex Smart can simulate a grade up to 7%, but that is based on someone weighing 75kg. A heavier rider will have an even lower limit.)
What Does It Do?
Lowering your Trainer Difficulty decreases the resistance changes on hills. You still have to put in the same amount of power to get up (and down) the hill, but the resistance will change less when you hit a hill.
Another way to look at it: where you might typically use 7 of your gears when riding at the default 50% setting, lowering it to 25% would let you ride and only use ~3 gears, since the uphills and downhills will feel less steep.
Increasing your trainer difficulty, on the other hand, will force you to use more gears. So instead of 7, you may use 10 or 12, since the hills will feel steeper.
What Does It Not Do?
It is important to understand that lowering or raising Trainer Difficulty does not make your ride easier or harder in terms of power output. You still have to put out the same cumulative watts to move the same distance as before.
“Trainer Difficulty” really is a misleading name for the setting–something like “Elevation Feel” or “Trainer Realism” may be better. As Chris Pollotta said on the Zwift Riders Facebook group, “It’s a cadence control more than anything.”
Getting Dropped On Downhills?
One common complaint from Wahoo KICKR owners is that they get dropped by other riders on downhills. (Anyone with a smart trainer will notice this, actually, but KICKR owners seem to have an especially hard time with it, probably due to the KICKR’s powerful flywheel effect.)
The challenge is that smart trainer riders (whose resistance is constantly changing to match terrain) are competing against dumb trainer riders (whose resistance is constant). A smart trainer attempts to mimic the feel of real-world riding, where it is difficult to maintain high power levels on downhills. For a dumb trainer rider, the downhill feels just like the uphill and the flats, so they can put out a lot of power on those downhills while the smart trainer riders spin out.
On uphills the opposite happens–smart trainer riders often pass dumb trainer riders, because the dumb trainer riders must shift to a harder gear to generate the increased power needed to keep up with the smart trainer riders. Most dumb trainer riders figure this out pretty quickly, though, and learn to shift as needed.
Smart trainer riders get a bit of a raw deal here, because they have no choice but to spin out in their hardest gear on fast downhills, while dumb trainer riders can fix their uphill challenges by shifting properly. But this is a necessary evil if Zwift wants to have lots of riders embracing the platform.
What does this look like when riding Zwift? As a smart trainer rider, I find over and over again that when I hit uphills, I pass lots of riders. And when I hit downhills, lots of riders pass me! This “yo-yo” effect can be especially annoying when you’re racing and it leads to gaps with groups you’re trying to hang with.
What’s the solution? Lower the difficulty slider to 25-40%. This will make hills seem less steep, and allow you to put more power into the downhills. Give it a try and mess around with the setting until it feels good to you.
Should I Change My Trainer Difficulty Setting?
I wouldn’t change the setting if you are happy with the “feel” of your rides in Zwift. If you think you’d like to adjust it, though, go ahead and give it a try–you can always set it back to 50%.