Ah, Trainer Difficulty. Simultaneously the most misunderstood and controversial setting in Zwift’s menu.
What does it simple enough: Trainer Difficulty scales the gradients sent to your smart trainer. So if the slider is at 100%, your trainer is being sent the same gradient you see on the screen. If it’s at 50% (the default setting), your trainer is being sent 1/2 of the gradient you see on screen. So at 25% Trainer Difficulty on a 10% climb, Zwift is telling your trainer to replicate the resistance of a 2.5% climb.
Still confused how it works? Read Using the Trainer Difficulty Setting in Zwift
While explaining Trainer Difficulty to one Zwifter recently, I was asked so what’s the best place to set Trainer Difficulty? And I realized that’s not a simple question to answer! So I’m going to answer that question here, instead of burying it in a Facebook thread.
A Multifactorial Problem
There are several factors to consider when choosing your ideal Trainer Difficulty setting. I’ll discuss each below.
#1: Your Trainer
How much resistance can your trainer replicate? And does your trainer have problems with overheating on long climbs?
Higher-end direct-drive trainers can replicate gradients of 20% or more, but lower-priced smart trainers such as the popular Tacx Vortex Flow may only be capable of replicating the resistance of a 6-8% climb. If you set your Trainer Difficulty to 100% and your smart trainer can only replicate a 6% incline, that means the resistance you feel at 6% will be the same at 15%. Which isn’t ideal!
And this is a big reason why Zwift defaults to 50% Trainer Difficulty – because it allows even lower-end smart trainers to continue adding resistance as you hit steeper climbs, even if the trainer is capped at 6-8%.
Overheating is a problem we see in some trainers, even very popular ones. It happens when riding on long climbs at high Trainer Difficulty, which forces the trainer to work hard since applying the resistance break at low flywheel speeds takes a lot of mechanical force. If your trainer begins to malfunction on long, hard climbs, you’ve got two easily solutions: point a fan directly at the trainer’s flywheel to keep things cool, and/or reduce your Trainer Difficulty so the brake doesn’t have to work so hard.
#2: Your Weight
When is max incline not max incline?
The heavier you are, the more resistance your trainer must apply in order to replicate climbs. In fact (and this is a bit of a rabbit hole), most smart trainer companies use a 75kg rider when calculating their estimated maximum incline. If you’re a 100kg rider, your trainer can’t replicate the gradient listed in the specs – but if you’re a 60kg rider, it can actually replicate a higher gradient than specified.
So how should your weight affect your Trainer Difficulty setting? Just know that the heavier you are, the more resistance you’ll feel on the climbs. If you’re running out of gears and having to grind your way up hills, it’s probably time to lower your Trainer Difficulty so you can at least pedal at a cadence that doesn’t make your knees sore.
#3: Type of Route and Race
Are you racing on a flat route, or up a big climb? Is your race a TT, or a draft-enabled event?
It may seem odd, but many Zwift racers turn Trainer Difficulty up for flat races, and down for climbing races. Why? Because they want the gearing flexibility of low Trainer Difficulty on long climbs, while high Trainer Difficulty lets them “feel” slight changes in gradient on flat routes such as Fuego Flats.
High Trainer Difficulty on flat routes makes even more sense if you’re racing a time trial, because it lets you feel those false flats and apply a bit more power to keep your speed high. Without having your Trainer Difficulty set high on a flat route, you may be on a slight incline and not even notice the difference – until you realize your speed has dropped by 2kph!
#4: Outdoor Training Goals
Does your Zwift training replicate your outdoor target event(s)?
Many Zwifters train indoors for big events or races outdoors. That race may be a pan-flat criterium in Florida, or a massive multi-day Haute Route event in the Pyrenees. It wouldn’t make sense to set your Trainer Difficulty to 100% and attack major climbs in Watopia in order to prepare for the pan-flat crit. But it also wouldn’t make sense to ride flat routes or set your Trainer Difficulty to 20% if you’re training for massive climbing days!
Use Trainer Difficulty to replicate your event. If your event is flat, leave Trainer Difficulty low and enjoy that high-inertia feel of spinning along a flat road. But if it has a lot of climbing, you’ll want to keep Trainer Difficulty high, so you’re feeling similar gradients and riding at low inertia just like the outdoor climbs.
#5: Indoor Bike Gearing vs Outdoor
How does your indoor bike compare to your outdoor one?
Now that Zwift has been around for 5+ years, more and more Zwifters have a dedicated indoor bike as well as their outdoor bike(s). Often the gearing on the two bikes doesn’t match, (especially if you use an old ride for your Zwift bike like I do). Trainer Difficulty can help this, though! If you’re concerned about replicating the feel of particular climbs which you might be riding outside, you can use Trainer Difficulty to make your indoor bike’s cassette “narrower” or “wider” to match your outdoor bike’s gearing.
There’s probably a mathematician-physicist out there with a formula to figure this all out, but I would just do it by feel. Perhaps your indoor bike is an older rig with a 10-speed 11-25 racing cassette, but your outdoor bike has an 11-speed 11-32 for climbing. Assuming the climbs you’re choosing on Zwift mimic those you’re training for outside, simply reducing your Trainer Difficulty down to 75% or so should give you a similar feel as your 11-32 cassette would if you were using your outdoor bike on Zwift.
#6: Spinning Out on Descents
Do you need more to push against on the downhills?
Trainer Difficulty banter often ignores the fact that the setting affects the feel of downhills as well as uphills! If you’re spinning out on descents, reducing Trainer Difficulty and/or changing your gearing are the only fixes. (Well, that or just going slower…)
Little-known fact: Zwift only sends half the descent gradient to your trainer. So at 100% Trainer Difficulty on a 10% downhill, your trainer is replicating a 5% downhill. At 50% Trainer Difficulty, it’s replicating a 2.5% downhill.
#7: Lower for Draft-Enabled Racing
How much shifting can you handle?
I don’t have access to the stats, but my guess is the majority of Zwift racers run their Trainer Difficulty below 50% when racing. Why? Because it keep their effort more even, reduces the need to shift gears, and ensures they won’t run out of gears on descents.
Some racers are purists (or perhaps are training for hard climbing races outdoors) and ride at 100% Trainer Difficulty. But more racers are pragmatic, and a lower Trainer Difficulty should generally result in a lower VI due to less resistance fluctuation. For many riders this means the overall effort might feel easier at lower Trainer Difficulty, since maintaining steady power is easier than doing intervals.
#8: Training for vEveresting
Training for the big one?
The official vEveresting rules state that you must complete your effort at 100% Trainer Difficulty on an electronically controlled smart-trainer. So if you’re doing a vEveresting effort, or just training to do one… you’ll want that slider set all the way to the right.
What Do I Do?
So how do I handle my personal Trainer Difficulty setting? It generally stays around 30%, except when I’m doing a flat TT and remember to bump it up to 70-100%.
At these settings I never spin out on descents, I never run out of “easy gears”, and I can feel slight changes in gradient during TT races where it matters most. (I’m fortunate to ride a nice Wahoo KICKR 5 in an air-conditioned space, so I don’t need to worry about overheating or maxing out the simulated gradient.)
What’s your Trainer Difficulty philosophy? Do you set it and forget it? Change it for racing on various routes? Share below!