(Andrew Jarrod) #1

Hi.  Is the hill simulation resistance with a Smart trainer (I’m using a Neo specifically) setup to be accurate to the real world or is it dumbed down slightly to gamify the experience and make it more fun ?

I’d like to know whether when I’m riding up a 10% gradient in game, am I experiencing the same effort it would take on a 10% gradient in the real world ?


(Mark Hewitt) #2

Go into the settings and you’ll see a difficulty level. By default it’s set that hills should be simulated at 50% of their true grade. You can turn it up to 100% if you like.

(Andrew Jarrod) #3

Wow ! 50% ! I feel such a cheat.  

So each 8% hill was only 4%. Every 100ft reported of elevation gain is really only 50ft. 

I assume therefore that all Strava elevation information is wrong by the same factor and calories burned in Strava is also considerably warped. 

This makes me tempted wonder if I should break the Strava link  


(Mark Hewitt) #4

Yes and No. You have to remember that all you’re doing in Zwift is inputting a power number into the game and that translates to the speed of your rider. So although you may only ‘feel’ 4% in terms of what gears you need to be in etc, the power output you need to generate for the speed you achieve in the game is accurate for an 8% climb, so the elevation counts and the likes are accurate.

It’s a useful thing because a lot of trainers aren’t good at simulating steep slopes especially at low speeds, and indeed I don’t necessarily want a realistic 8% slope on the trainer, but if you do, then by all means turn the slop up to 100%.

(Andrew Jarrod) #5

Thanks again Mark for the explanation.  I wish I could say that I entirely understand the answer, alas…

I understand you saying that I’d expend the same energy to climb the 8% hill in Zwift as I would in reality.  Which is good.  And that I’d have to exert the same power to climb the hill too.  Also good.

But I don’t entirely understand how I do this with only 4% resistance instead of the full 8%.  Does this mean that I’m effectively pedalling twice as far to make up for the halved resistance.?

(Mark Hewitt) #6

I don’t claim to fully understand the physics myself ;). But yes, that’s basically it I think. Again it’s worth reiterating that the *only* thing that matters in Zwift is your power output, the slope on your trainer is only really there to add to the immersive feel of the game. People without smart trainers won’t get any slope at all and yet they still need to expend the same amount of power to get the same speed up each climb.

(Ben Crone) #7

You can think of the % difficulty as adding extra gears to your bike. At 50%, an 8% gradient will *feel* like 4% gradient but because you’re in a ‘lower gear’ it takes you longer to get to the top of the hill.

Imagine riding a real life hill on a road bike and then again on a mountain bike. Same hill, different difficulty, different time.

The physics part:

  • Regardless of trainer difficulty, each hill (zwift or otherwise) requires a given amount of energy to reach the top.
  • Power is the rate at which a rider is expending energy, so the power a rider outputs determines their time up the climb.
  • Power is the product of torque (force through pedals) and cadence.
  • Changing the trainer difficultly, much like changing gears, changes the amount of torque required to turn the pedals.

So regardless of trainer difficulty, zwift requires the same energy to reach the top of the hill. Similarly if you output the same power you will record the same time regardless of trainer difficulty.

All the trainer difficulty is doing is allowing you to tune the ratio of torque and cadence - exactly like your gears.

(Andrew Jarrod) #8

The fact remains though that on the normal settings (that everyone else is using too) an 8% hill is actually a 4%er.  So when you go out in the Spring and attack the 8% hill in the same way you do on Zwift, your legs will fall off.

(Ben Crone) #9

I don’t think you understand how power/gears work.


(Jeff Rensink) #10

Basically what they are saying is that it would take you the same amount of watts and time to climb the virtual hill that it would the real hill.  It’s just that you are putting out the exact same amount of effort in different gears.

All that seems to matter in Zwift is watts.  How fast your rear wheel is spinning is irrelevant.  So say it takes you 5 minutes to climb a hill while putting out 250w on average in Zwift.  Then you go climb the same hill in real life.  If you again average 250w, it’ll take the same amount of time.  So it’s the same amount of time for the same effort.

What’s the difference then?  You just happen to be in different gears.  Since you are “feeling” less slope in Zwift, it just means that you are spinning your wheel faster to hit 250w.  So to give a 250w hill effort in Zwift, you’ll be in a faster gear compared to doing the same 250w hill effort in real life.  But it will feel the same and take the same amount of time.

At least, that’s how I understand things to be.  Someone please correct me if I’m wrong.

(T hird Wheel [KRT]) #11

I am just wondering how this will affect gradients of 4% or lower (to say -10%) as at those gradients wind resistance starts to play a major factor.  A 4% hill becomes a 2% which might be 20mph which starts to become an air resistance issue which would negatively impact your average speed? On a negative gradient say -10% you actually on doing -5% which again would mean you lose out on speed due to a flatter downhill, less gravity effect meaning less speed?

In Zwift if you are using a powermeter like Stages, does it adjust the speed to the stated gradient? Or does it also do some adjusted calculation? 

(Mark Hewitt) #12

As myself and others have explained above, if the hill is 4% on Zwift then the simulated gradient is always 4%, with associated gravity, air resistance (no wind on Zwift) and every thing else involved with that.

A 10% simulated downhill is simulated as … 10% with the gravity effects present therein.

The ONLY thing the difficulty slider does is alter the resistance put onto the trainer.

If you have the setting at 100% difficulty and you climb the hill at 200W. Then you put it back down to 50% difficulty and climb the hill again at 200W then the time taken to climb the hill will be *exactly the same*, the only difference being that you’ll be able to use higher gears to do it.

(H Cinelli ZSUN) #13

While I understand the power/gear and difficulty setting relationship I’d like to elaborate on what Andrew might be getting at.  I know most trainers don’t do 10%+ hills realistically very well, especially for heavy riders like myself, but it’s one thing to get good at spinning up a 4% grade and another to spin up 8%.  Not to mention when the grade forces you to get out of the saddle, which we all love :slight_smile:   In that way, your legs will fall off if you are only used to half the grades in game vs real life because you’ve basically only trained high cadence / low resistance in zwift.  

(Mark Hewitt) #14

Indeed. You just have to be aware of that fact and don’t kid yourself that you’ve been training on 10% when you haven’t!

Of course it’s still only really an issue if you’re already in bottom gear and you can’t keep up your cadence.

(Johnny van Gesink) #15

I have difficulty set at 50% (default), but I climb the 10% climb’s at almost the same gearing as I would a 10% climb in real life. I feel that a 100% setting would be much harder in Zwift than in real life.

By the way, I use a Tacx Bushido Smart in combination with a Stages PM