Think you know everything about how Zwift’s Trainer Difficulty setting works? Our favorite Aussie lama Shane Miller just released a video showing how Zwift treats gradients on downhills differently than uphills. Watch it now:

To summarize the video: Zwift only sends half the gradient to your trainer on descents. So if the screen shows you’re on a -10% downhill, Zwift is only going to send -5% to your trainer.

BUT… and here’s the big but… your Trainer Difficulty setting will further reduce the gradient if it’s set below 100%.

For example, if your Trainer Difficulty is set to 50% (Zwift’s default), Zwift is actually sending just 1/4 of the downhill gradient to your trainer, because it first halves the gradient, the halves it again. Here’s a simple table showing the actual gradient in game, and the gradient sent to your trainer based on different Trainer Difficulty settings:

Gradient25% Trainer Difficulty50% Trainer Difficulty100% Trainer Difficulty
10% (Uphill)2.5%5%10%
-10% (Downhill)1.25%2.5%5%

But Why?

Shane explains in the video that this setting was put into Zwift early on to avoid riders spinning out on descents. In order to put out watts, we need resistance to push against. But on steeper/longer descents, smart trainers would just spin out, leaving us with nothing to push against. Just like outside!

Except outside, it’s fun to coast down the hills. Indoors: not as much. We’re often looking to keep pedaling and continue our effort, and we don’t want a long descent interrupting that.

Digging Deeper: Saving the Smart Trainer Users

That’s the simple explanation of “why.” But let’s dig a little deeper and consider a typical Zwift race situation with riders on dumb trainers (using a power meter on their bike, of course) and riders on smart trainers.

We understand that when these racers hit a downhill in game, the smart trainer riders feel the resistance drop, while the dumb trainer riders feel no resistance change. Simple enough.

But what if Zwift didn’t reduce the downhill gradients, or offer a Trainer Difficulty setting? Smart trainer riders would be at a major disadvantage on downhills, because they would find themselves with nothing to push against while the dumb trainer riders had plenty of resistance.

For more on this line of thought, read “Hanging with the Group Over Gradient Changes

So that’s why Zwift halves the descent gradients. And it’s also another reason why Zwift created the Trainer Difficulty setting in the first place!

Your Thoughts

Did you know Zwift halved descents? Does this seem like the best way to do it, or can you think of something better? Share below!