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:
| Gradient | 25% Trainer Difficulty | 50% Trainer Difficulty | 100% 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!
Interesting post. I race on zwift quite a bit using a wahoo kicker and always feel like I’m working really hard on the descents whilst quite a few people just cruise past hardly pedalling. OK I’m not the heaviest rider at 65kg which I understand is one factor to this but I was also told your trainer type can have a big impact. One of my friends has a tacx neo 2 and on the downhills the trainer drives for you so you don’t need to pedal apparently.
I’m assuming this means nothing for speed. If you coast down a hill out wouldn’t matter if your trainer difficulty is set at 0 or 100. It is a set parameter. The trainer difficulty is a setting of resistance if you want to pedal and add to that speed. Which like flats and uphill all it does is basically change your gearing.
Nah, the Neo’s downhill drive doesn’t make it easier to go down hills. Just makes the feel more realistic.
Lighter riders often complain of being dropped on descents, but it’s no different outdoors. Keep your watts up over the crest of the climb then get in the draft and hold the wheels, and you should be good!
Thanks for sharing! That actually makes a perfect sense and is in fact very smart to manage things. Well done to anyone who came up with that idea. It is exactly the case that outside, it’s fun to coast down the hills. Indoors: not as much…
on the other side, dumb trainer users have almost no chance to win a real bunch sprint with 13-17w/kg, because the resistance is too low (max 12w/kg I would say).
Perhaps, although I’ve known some top A racers who use(d) dumb trainers and win and sprints.
Depends on the trainer I guess? I have always used a fluid dumb trainer on Zwift with a power meter, the resistance increases as the wattage does. So, while I’m no Kittel, it’s not a limiting factor and I put out those kinds of w/kg…unfortunately not for long but that’s down to the body being the actual limiting factor not the trainer! What’s striking is that Zwift has taught me to put out nearly the same max watts inside as outside, despite it being a weight on trainer – i.e. I can’t stand up at high wattage without the rear… Read more »
@guest_32812 and a rocker plate!
Ha, maybe! Light hearted comment I know but as an aside I’ve tried a Neo and really didn’t like the (to me, unnatural) sway. In contrast I liked the static, solid, robust feel of a Kickr. I totally get why people go for rockers I just find it hard to imagine them being comparable enough to riding a bike outdoors (NB I’ve haven’t tried even one so totally unfairly speculating!). If it feels off or contrived I’d rather it be static. Maybe riding on a giant treadmill would do the trick? If someone could just design then give me for… Read more »
Rockr’s are more comfortable on a long ride too. I’ve found I can stay on the bike for 3-4 hours with out a numb bum with a rocker plate. The Kickr climb helps too.
Eric, do you think (or know) that TD also affects drafting? Because, as per your great articles, i can understand that when you draft (and double draft!) you can really feel the effect on your effort, and you can be with the group while pushing less watts. But i never feel, even double drafting, such big relief from it; would be my around-30%-TD the actual motivation for that? So, less TD, less descent gradient, and also lee drafting effect?
There is no draft feel on Zwift – that is, you don’t feel the resistance drop when you go into the draft, or increase when you go off the front. I’ve actually written about this, because I think it would be a really cool feature to have! See https://zwiftinsider.com/feeling-the-draft/
So no, Trainer Difficulty doesn’t affect drafting in any way.
Hi Eric – First, thank you for all of the information you post. It is truly helpful.
I am confused by you comments on the lack of Draft Feel. In a previous article you verified the reduction in power required on climbs, flats and descents to maintain your position in the draft (https://zwiftinsider.com/draft-savings/ ).
Wouldn’t this drop in wattage requirement be the “feel” that you describe?
I believe the “feel” is in reference to your smart trainer changing resistance. Yes it takes less watts to maintain pace. In real life you would feel less wind resistance making it easier to pedal. Like hitting a slight decline. If zwift would make a trainer resistance change when you draft it would have more “feel”.
Hi Rory. I apologize if I am being dense on this topic. But two questions: 1) If my wattage drops from 300 to 270 once I enter the draft, wouldn’t you feel that drop in power output? 2)If my cadence remains the same as I enter the draft, and my power output drops because I am in the draft, doesn’t that mean that the trainer does indeed change resistance? It seems that if the power output of a rider drops or is lower when in the draft of another rider, either of two things need to have occured; either the… Read more »
Resistance doesn’t change in the draft. Your power output only drops in the draft if you purposely drop it.
I hate to question the Zwift Insider but are you sure about that? This morning on the Fuego Flats (out to the town only) in which I stayed in the same gear and attempted to maintain constant 90 rpm cadence. In the first part of the ride I found myself passing or being passed by a number of groups so I was in the draft almost always. The second part of the ride I was mostly alone. During the first section of long flat road my watts were pretty consistent at 160. The second long flat section my watts were… Read more »
All I can tell you is what Zwift has told me–and my experience in game backs it up. Keep in mind on Fuego Flats there are a lot of slight inclines and declines (.4% up or down) which show up as 0% gradient. So it could be you were on slight inclines or declines, which would affect things.
Depending on the trainer you are using it might well be warming up too. For example on my primitive, dumb, fluid trainer with a crank based power meter the watts change considerably for the same gear/cadence for the first 20 or so minutes. In my case the watts start low, rise then fall a little then finally stabilise. In other words the resistance I’m pushing against changes as the trainer warms up so although my cadence/gearing may remain consistent my power doesn’t.
My understanding of zwift drafting is like this. I may be mistaken but Eric, correct me if i’m wrong. In real life you can feel the draft because the wind resistance decreases. You would be able to feel this even if you were cycling blind. Just like changes in gradient. Zwift requires you to look and decide where you want to be in the group. If you decide to ride behind some people then it will require less power to stay in that position. The trainer will not feel lighter when you enter the draft, It just allows you to… Read more »
I tried Bkool recently and there you really feel the draft in you resistance, it’s great!
Very interesting! It seems the tech team at Zwift really do know their stuff. 😉 Thanks (and also thanks to Shane Miller) for the explanation! The one thing I loved about my “dumb” setup I used to have was being able to power away on the downhills. Much harder (and more realistic) now that I’m on the NEO. Great that they kept some resistance so as not to spin out in races.
Thanks so much for posting this. I’ve known for a while that my KICKR Climb halves the descent percentages when on 100% trainer difficulty – something I find mildly irritating. But now I understand something broader is going on and it’s not just an arbitrary decision to limit the Climb and KICKR Bike. While I don’t love the limitation it places on the Climb, as a lightweight rider, I’m not sure I’d want to lose any more ground than I already am on descents and not be able to put any power into the pedals. So maybe the setting makes… Read more »
Some trainer needs to introduce a “stomach drop” + “sketchiness factor” where your trainer jerks like you are just about to lose wheelgrip. (Of course there is no braking so what would you even do about that.) #YOLO #meatmotor
Hello, Im wondering about advantage/disadvantage with Wahoo Bike on descents. This Bike has a Motor. If you go with TD 50% the Motor does not work in Descents like with 100%. Ive made a Test: If I go on descents with 30% my avatar goes in superduck position with 0Watts. If I go with TD 60% and above my avatar does not go in superduck position, but my trainer Motor does send Output Watts nearly 50 Watts without pedaling. So I wonder: would it be an advantage in races to set the TD on 100% so I have the full… Read more »
I’d say if the bike is adding ANY wattage at any time, you need to contact Wahoo and get that fixed. If you aren’t pedaling, it should say 0 watts.
Does this apply in the tuck? Will riders of the same weight descend differently, depending on trainer difficulty setting? Both descending 10% gradient but actually one is descending 5% while the other 10%?
@Tom Harvey’s question, this is exactly what I am wondering. Any insight?