“Trainer Difficulty” is absolutely the most misunderstood item in Zwift’s settings menu (Menu>Settings). Visible only to smart trainer users, Zwift’s support docs explain the setting like this:
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).
Trainer Difficulty is set at 50% by default, 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 feels like a 5% grade in the real world.
Why does Zwift default to 50% and not 100%? I’m not completely sure, but my guess is it has a lot to do with lower-end smart trainers only supporting maximum grades of ~7%.
What Does “Trainer Difficulty” Change?
Lowering your Trainer Difficulty decreases resistance changes on hills. You still have to put in the same amount of power to get up (and down) the hill, but you will “feel” the hill less.
Another way to look at it: the Trainer Difficulty setting determines how much shifting you will need to do. 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 and you will need to shift more to maintain a healthy cadence. As Chris Pollotta said on the Zwift Riders Facebook group, “It’s a cadence control more than anything.”
What Does It Not Do?
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.
That said, a higher Trainer Difficulty will result in a higher VI due to more resistance fluctuation, which usually means your overall effort will feel more difficult. Because maintaining steady power is easier than doing intervals!
“Trainer Difficulty” really is a misleading name for the setting. Perhaps “Gradient Feel” or “Trainer Realism” would be better.
Getting Dropped On Downhills?
One common complaint from smart trainer owners is that they get dropped by other riders on downhills.
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’s the solution for smart trainer riders? 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.
For more on this topic, read Hanging with the Group Over Gradient Changes.
Should I Change My Trainer Difficulty Setting?
No need to change the setting if you are happy with the “feel” of your rides in Zwift and you aren’t struggling with yo-yoing in and out of the pack on group rides. 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%.