Editor’s note: this article originally ran on Jordan’s website at meatmotor.com. We appreciated Jordan’s alternative view of Trainer Difficulty and loved his willingness to sweat for science, so we asked if we could share his findings with our audience.
Jump Straight to the Gearing Results
Perhaps there is nothing more misunderstood in the Zwift world than trainer difficulty.
Some people have (wrongly) postulated that if they are racing with the Difficulty slider at 100% against someone racing at 50%, they are at a disadvantage. This is not mathematically true. In Zwift, watts are watts. The difference is the feedback in terms of resistance your legs get on an incline (and decline).
On Zwift, keep in mind you have a virtual rider who is propelled by watts. You also have the real world you in which you create those watts.
There are two ways to generate more watts. (1) Press harder on the pedals (force/torque) or (2) spin the pedals faster.
Zwift Trainer Difficulty is said to be a decrease in the gradient of a hill in terms of what is presented to your legs in terms of resistance on the trainer.
- At 100% Difficulty on a 10% gradient, you feel the full 10% in terms of pedal resistance.
- At 75% on a 10% gradient, you are only experiencing a 7.5% gradient in terms of pedal resistance.
- At 50% Difficulty, that hill is now a 5% gradient in terms of pedal resistance.
And so on…
Here are how things even out. Your on-screen-rider is STILL going up a 10% gradient and needs that amount of virtual watts to get up the climb even though your Trainer Difficulty can make the gradient feel reduced to you the real-rider.
So if you are racing someone and they are at 100% difficulty, and you are at 50%, their trainer resistance will be higher, and they will be putting out more force and watts than you at the same cadence as you. To keep up with the 100% rider in the same IRL (in real life) gear as you, you will need a much higher cadence to output the watts needed to drive your virtual rider up the climb.
So a good comparison/analogy is to see trainer Difficulty as your available gear selections. But realize that your available gear selection changes based on the gradient of the hill.
At 100% difficulty, you are locked into your real-world gearing on your bike. So if you are riding a steep climb in your granny gear of 34×28 is too difficult to spin at 80 RPM cadence, all you can do is reduce your cadence. Just like IRL, you’ll be slogging up that hill at some incredibly low RPMs (aka the dreaded 50 RPM climb). This is usually not the most advantageous physiological means to get a bike up a hill. There is a lot of taxing on the muscular system at 50 RPMs cadence.
But, with the Difficulty reduced to 75%, you now have a bigger granny gear at your disposal, and at 50% an even bigger one. You can now spin at higher cadences than you could on your real-world gears. (But don’t forget, you’ll have to spin faster to go the same speed online).
[adinserter block=”1″]
But Just How Much Bigger Are the Gears at Each Percentage?
Ahhhh, time for an experiment and a report.
Test method:
- Climb up a specific segment of Alpe du Zwift that is a 10% gradient at the same cadence but with different difficulty settings. In this experiment, cadence is the constant in the equation. I chose 80 RPMs because it seems like a good balance between grinders and spinners. I chose the 10% segment because that is a solid round number.
- Trainer Difficulty is the variable. The test was performed at 100%, 75%, 50%, and 25% difficulties.
- Speed will be the outcome. Spinning at 80 RPMs at 100% difficulty makes your virtual rider go faster than spinning at 80 RPMs on 75% difficulty. So the speed in mph is the important piece of the experiment.
- Once we get the speed for each difficulty level, we can reverse engineer the speed at cadence to approximate the gear using Sheldon Brown’s Online Gear Calculator.
Note: I ran this test twice at each Difficulty, but it needs more repetitions to be definitive. Also, the gradient does affect the results. A lesser gradient would be a smaller equivalent gear difference. But 10% is a pretty classic climbing percentage, and Alpe du Zwift is the most iconic climb (granted the overall ADZ climb averages 8.5% overall). When I have time, I’ll rerun this on this segment and at other gradients.
Setup data for the experiment:
- 77 kg rider on Zwift.
- Sheldon Calculator inputs using 700ccx25 tire and 172.5mm cranks. Yes, I am using a direct drive trainer IRL, but I had to pick something for that value.
Test results:
- Runs at 100% Difficulty and 80 RPM Cadence on 34×28 (2 run average)
Speed achieved in Zwift 7.98 mph - Runs at 75% Difficulty and 80 RPM Cadence on 34×28 (2 run average)
Speed achieved in Zwift 6.54 mph - Runs at 50% Difficulty and 80 RPM Cadence on 34×28 (2 run averages)
Speed achieved in Zwift 4.65 mph - Runs at 25% Difficulty and 80 RPM Cadence on 34×28 (2 run averages)
Speed achieved in Zwift 2.69 mph
Then we reverse-engineered the equivalent gears on Sheldon’s calculator.
The Results
| Difficulty Setting | Gear Equivalent on 10% Climb | Watts Required for 80 Cadence |
| 100% | 34 x 28 (real-life test gear) | 311 watts |
| 75% | 34 x 33 | 248 watts |
| 50% | 34 x 46 | 177 watts |
| 25% | 34 x 77 (aka the whopper) | 93 watts |
This is what you really wanted to know. Thanks for sticking around.
[adinserter block=”7″]
Summary and Insights
You can get some whopping big granny gears in Zwift using the Trainer Difficulty setting. For riding inside the Zwift world, you can virtually swap out your cassette just by reducing the percentage. Spin like Froome or grind like Ulrich, whichever you prefer to go fast.
On a 10% climb, reducing the difficulty to 25% means that you have a massive gear available to you. Granted, you will need to spin the snot out of it, because at 80 RPM and 2.69 mph it will take you 2 hours and 47 minutes to arrive at the summit. Of course, you can always run at 25% difficulty and simply use a bigger real-world gear. Heck, run your big ring and feel like a pro.
When racing, you can reduce Trainer Difficulty, just realize on every incline you’ll have to spin faster than your competitors due to the decrease in gradient effect. As you see in the chart above, you are at 25% difficulty and your opponent 100% spinning at the same cadence, you’ll get dropped like a hot rock.
One caveat, if you are going to do some massive real-world climbs, you might not want to not dial down the difficulty on Zwift. Instead, get used to grinding your real-world gear limitations once you run out of gears.
Questions or Comments?
Share below!
This needs to be pinned at the top of every online forum. And no Zwift user should be allowed to post anywhere until they pass the Trainer Difficulty Exam.
I am glad you found it valuable. Thanks!
Climbed Ven-Top yesterday and ended up with 25% TD so I could spin in the high 60’s at 11%. Don’t think I’ll be doing Ventoux any time soon.
I was thinking exactly that when going up Ven-Top at 50% the other day. Need to loose 10kg before ever attempting IRL Mt Ventoux. Some day I will re-try Ven-Top at 100%. Some day, just not today. 😊😊
I feel the key point here is being missed; if you are putting out 200w, it does not matter what gear you are in IRL or what the trainer difficulty is set to, your speed will be the result of the power, you weight and height, the gradient, and the zwift algorithm that combines these factors. The most practical result of reducing trainer difficulty is that you do not need to change gear as much to maintain power at same cadence. At the limit, if trainer difficulty was zero, there would be no change in trainer resistance with gradient. IRL it would feel like you are constantly riding on the flat whilst in zwiftland your avatar’s speed would vary with the terrain. This would of course be very dull and make your smart trainer a pointless waste of money. On the other hand if you set difficulty to max, then you will need to change gear more often to maintain your cadence in a good range. And at the limit (for example the radio tower climb) you may find that you do not have a low enough gear IRL to keep your cadence comfortable. In which case reduce the trainer difficulty.
FromYou are correct. The point of the experiment is that it was done in a granny gear. The main problem with climbing IRL and/or on Zwift is that you run out of gears and then end up climbing at a ridiculously low cadence that is inefficient. This test was to see what equivalent easier gears you can gain on a 10% climb by dropping the TD so that you don’t “gear out.”
Keep in mind that really easy gears are also inneficient and impossible to hold irl because loss of balance.
Nice experiment. I would like to have it tested another way around.
Set the watts at e.g. 250w
Put the bike in granny gear
Record the different cadences at 100%, 75%, 50%, 25% and then calculate the equivalent gear ratios for each difficulty.
This would then show that a 34/28 is equal for example to a 34/30 at 75%
This test could be done for all the common granny gears. 39/25 etc
Somebody could build a calculator. Enter your desired climbing watts, enter your current granny gear, enter the max gradient of a climb and the Trainer Difficulty could be calculated for you.
Definitely agree. The article states you need to spin faster but gives no clue as to how much. 311w is 80rpm @ 100% 126rpm (???) @ 50%.
That gets to be quite complicated math for everyone to use, because the equivalents will vary by each .001 KG difference in weight of the rider. I can definitely run it that way for a given weight, but beyond that, we’d need some access to the Zwift algorithm. Also because the gradients don’t hold true over an entire climb, but rather vary, the ratios vary. While it could be perhaps calculated at max gradient, your average gradient power wouldn’t match up. Or you could calculate it at average gradient and you could still gear out if a section, is say, 18% on a climb that averages 9%.
The maths would indeed become complicated (without the algorithm)! That is why I said someone else should come up with a calculator 😉
Simply, Zwift should never have used the word difficulty. It could have been implemented as a granny gear calculator, but then they might have confused the novice riders and insulted grannies! A no win situation….
But thanks again for this post. I think the link to this article will be pasted often in the FB comments!
I had the same thoughts as well. I have a NEO Bike and can electronically change the gears pre-ride. I always thought what gear should I swap for 32 for…maybe a 40 for steep climbs.
One issue that still puzzles me is; back when I started on zwift, the trainer dificulty was at default value” whatever that normally is” back then I was putting out crazy watt number like 450/470 watts, than I became awhere of the trainer dificulty setting and I set it approx 80/90%. Since than I started to see more realistic wattage from my training session… any one able to explain this please! really would like to understand it.
The default is 50% difficulty. The only way to explain this is
1. Your trainer is better calibrated now or your powermeter is better calibrated, whichever you are using to input power.
2. You are simply more efficient as mashing bigger gears physiologically (highly doubtful).
There is another thing that is important to mention, and that is inertia. The better smart trainers simulate the ‘feel’ of a climb by altering the inertia and the effort required to overcome that inertia and spin the flywheel. It is a simply a linear increase in resistence (which is the case for a wheel on trainer). This is another reason why it is important to state that what changes with TD is the gradient sent to the trainer. That gradient can be interpreted by the trainer in different ways, but on a good turbo like my Tacx Neo Smart Bike, 90rpm for 250w on a 10% climb and 90rpm for 250w on a 2% climb (different gear selected) DO Not feel the same.
That should read ‘It is not simply a linear increase in resistance’
Yes, that math gets crazy quickly because of different flywheel weights, friction, etc. And 90rpm at 250w on 2% would result in a much higher speed than at 10%.
But physiologically speaking, 90rpm @ 250w is the same regardless of the gradient. (Example: If I blindfolded you and could somehow still get you to put out 90rpm @bradmays watts, you’d have no idea if you were going uphill, on a flat, on downhill if you were inside with no Wahoo Climbr present. The watts ARE the measure of how “hard” things are. If it were “harder” it would require more watts (generated either by higher cadence or more force).
Sorry Jordan but this is not correct. There are physiological differences between riding on the flat and riding up a steep gradient, this is why people tend to self-select a lower cadence on a climb even when not in their lowest gear. This is also the reason why trainers have heavy flywheels, because it feels like riding up a 20% slope through sand without it.
There have been a few scientific studies looking at the differences (I can’t be bothered finding them now) and it comes down to inertia. When riding on the flat at high speeds people tend to apply force to the pedals through a smaller range of the pedal stroke using the inertia to carry them through the rest of the stroke. They therefore use a slightly higher cadence to apply the shorter force intervals more often.
On a climb, particularly a steep one, this inertia is lower or absent. The force applied to the pedals therefore has to be more continuous. It tends to start higher in the pedal stroke and continues for longer. The difference is not massive, a few degrees probably, but enough to make a difference. As with everything people will naturally have different strengths in how they make power, and what they have trained for.
The difficulty setting is therefore not just a gearing range selector as many people think. The top indoor racers tend to use a lower difficulty setting as it allows them to stay in a narrower “inertia” range (for lack of a better term) where they are more efficient. They still have to make the power, but they can do it at their optimal cadence at all times.
It would be cool to see downhill equivalents to. Is riding at 25% TD like having a 52×5?
No, it’s the opposite. You need to run a taller gear to make up for the lower TD. This effect is much more noticeable during flat workouts with specific wattage requirements. When we’re supposed to be generating 120 watts in a group you’ll be in your top gear spinning your ass off.
Mark is correct. It’s the opposite. There is a great video on that here: https://zwiftinsider.com/trainer-difficulty-on-descents/
This is great info. I always feel like I’m cheating using the 50% setting. But, I’m also riding a 53/39 crankset and an 11-25 cassette, so 50% just gives me a granny gear like many are using IRL.
You are not cheating really. Just IRL it will stink when you can’t access those additional virtual granny gears and are climbing at 35 rpm cadence. BTW, that’s beast mode gearing you use. Congrats!
Yep… Learned the hard way that I could have really watched my cadence/power when training on all de Zwift all those times before trying to PR up my Diablo. It was a big “derp” moment for me. Lol
i run my power much lower; so im never off the big chain ring; and i never have to worry about dropping a chain
Yep I just realised that my trainer bike set up is such that I could turn down TD a bit for those unrelenting climbs and it’s not cheating! (53/39 and 11-28) My new roadie for outdoors is a bit easier
good post, key take away for me – racing – As you see in the chart above, you are at 25% difficulty and your opponent 100% spinning at the same cadence, you’ll get dropped like a hot rock. So true need to pay attention and ramp up on every climb to not get dropped fast
The increase in resistance can and does send a signal to the brain to be alert, something might be fixing to happen (to use Texan language). Without any change, you might get caught mentally asleep. It’s why I’d never race on 0%.
Having always raced on a dumb trainer with the same pm I use on the road, you very soon get used to looking ahead and anticipating the increase in watts with every kick up 🙂
How does this factor in muscle fatigue?
A higher %TD results, inevitably, in lower cadence, which, in turn leads to quicker muscle fatigue. Studies have shown that muscles are far less fatigued at 100 RPM than at 60 RPM while pedaling at at the same watts output. As a result you get tired more quickly at lower cadence/higher TD and thus slow more quickly.
From a personal experience perspective, I spent my first two years on Zwift at 100% TD; having dropped it back to 50% since 2020 started (after a long chat with a fellow Zwifter) I find my FTP miraculously went up (from 260 to 290 – almost overnight). As it is less fatiguing so I can hold the watts for longer. Does anyone else find lower cadence/higher TD = getting more fatigued faster?
I have a MASSIVE article that looks at all the recent sports science legit studies on cadence, efficiency and speed/time to exhaustion in the works. Lots of discrepancies in the studies, so it is taking a bit. But I promise, it’s coming. (We’ll have a TL;DR one or two-sentence summary version, too.)
Opposite here. I find it much easier to maintain power at lower RPM. I can get a better FTP uphill at 60 RPM than doing FTP test on the flat at 100 RPM
I am the absolute opposite. Climbing ADZ on 50% vs 100% makes me lose 10 minutes. This is an abysmal difference. People need to realize that we are all different. I weight 66kg and as such i am very light. Grinding works great for me as i can sustain near my FTP (3.3w/kg) the entire climb. My muscles aren’t taxed because they don’t have to pull too much weight and my lungs are OK as i am not into high RPM’s. If i drop to 50% the added RPM’s will kill me after 30 minutes. I cannot match my watt output as it demands 80+RMPS while i usually climb at 50 rpms with heavier gears. All my rides have better times and higher average watts at 100%. I once changed my main Zwift device and for an entire month i had an horrible time trying to figure out why i was falling apart in performance. Even my Garmin made me fall from a score of 55 V02Max to 52. When i checked the settings i saw that the device had not taken in the settings previously imputed. The next ride after i put 100% my average watts for a regular ride was much more in line with the past. And this also explains why i had better performances while on Erg mode. Erg mode just erases the trainer difficulty and demands you to mput X watts no matter the gradient.
I’ll be honest on my last ascent of y 24 hour alpe Du Zwift challenge I went down to 25%
This is interesting article but does it miss one aspect of indoor training – at 100% gradient I usually have 1 or 2 gears spare when riding indoors compared to IRL.
I can spin “comfortably” up the alpe in 36×28 on 100% gradient, but doubt I could on 10-12% IRL.
Could just be me, different trainers, or general turbo stuff.
Yes, a IRL vs. virtual test at 100% would be fabulous. I just need someone to purchase me the ticket to France once COVID ends. ha!
GCN did the comparison https://youtu.be/YaoqPzDtRbs
Really interesting inside v outside comparison of alpe du huez/zwift but doesn’t answer the gearing question…
He mentions the average cadence difference overall between his efforts but also says he was out of the sadde more IRL where you’d expect lower cadence as a result
Indeed. At 100% difficulty i never go upwards the 3d gear while climbing ADZ. And this allows me to put much more watts. At 50% i would have to spin much more to match the watts and this would kill my lungs. In real life there’s no way i would be climbing 12% gradients in 3d or 4th gear with my heart rate perfectly under control around 155/160 BPM. I would probably be in 2nd (i always try to keep the 1st for when i am half dead and thinking about death) with my HR at 170+. This is a MASSIVE difference 20 minutes in when you still have 40 minutes ahead.
This is so useful as it perfectly lines up with my IRL experience of finding that my preferred cadence of around 78 rpm runs up against my threshold on longer double-digit gradient segments as that equates to around 300w with a 28 tooth gear. I bought a 32 to try for longer, steep climbs, and it seems from the data that I could climb comfortably at sweetspot for a while on a >10% climb with those extra teeth (especially as I’m a bit lighter than the 77kg model for this test).
Interesting. Do you that 78rpm is your self-selected cadence generally? That would definitely put you towards the bottom end of the spectrum in terms of self-selected cadence. I will be doing a poll as part of the upcoming Cadence article. I know polls are the same as the science part, but it will make a nice inclusion to say, “Science says this, but reality says that.”
Oh my, is that considered low? Then I’m ridiculously low 😀 On my “best performing” outdoor ride recently (55.5 miles with 3,100ft of elevation gain completed in 2h55m/19mph average) I ended up with an average cadence of 66rpm. Personally, I find I can grind for hours no problem but really start suffering when I have to spin for long periods of time. Zwift has helped me get used to higher cadences, but left to my own devices I rarely stray above 70 😀
Funny enough on easy rides I’ll tend to be lower, low 80’s, but I usually spin 95-110 RPM in races, with sprints up to 135 RPM.
Me and my mate mostly get in the 80’s every zwift ride….
A fun fact for TACX NEO 2 users … One cool feature of those trainers is that the trainer motor spins up when you go downhill which gives a touch of realism but I suspect my whizzing down the back side of many big climbs contributed to bearing failure in my unit due to the high spin rates for long periods. Credit to Garmin to replacing my NEO 2 under warranty but now when I’ve finished a big climb and just want to freewheel down I set my trainer difficulty to zero and enjoy the wear-free silence as I descend at the same speed. Thank you for the article Jordon …
Another option is to unplug your Neo, that also stops the freewheel.
Easier than dealing with an apple tv remote! 😉
The professional cycling coach I worked with for 3-plus years taught me that riders should never be grinding up a hill at a low cadence. Instead, the winning play is to find a gear you can spin at about 90 rpm and use that for climbing. I find I’m actually faster up hills both outside and on Zwift using such an approach. As a result, I love the trainer difficulty setting and have left it at 50% since the day i started Zwifting back in the fall of 2017. BTW, my granny on all my bikes is a 32–including the one mounted in my trainer for Zwift.
There is one less explained element here. You always assume the comparing riders are in the same gear combination, but one with lower difficulty can output the same power if they are in a higher gear. I personally believe that the difficulty can help with reducing the amount of gear shifts.
Also, as a good analogy, one can think of climbing at a reduced difficulty by imagining zigzagging up instead of climbing straight. You experience a smaller incline, but you have to go longer.
IMO, the only impediment is that one can get performances in Zwift that cannot be replicated IRL with he same gears. And when on an actual 15% climb, realize you cannot make it.
Yes, the assumption is that they are gearing out at 30×28 in this case. Of course, if they have different gearing (ex. one rider has a 32) those results will be different. I wanted to run an apples to apples comparison.
I think it’s also important to note that a lot of folks are still using wheel-on trainers and the effect is the same– you end up being able to “spin” up the steep ascents if you want because your own gearing determines your difficult setting. But you would still have to either soon higher at same getting it else bump up the gearing to make the same watts/speed up the hill as sometime on a smart trainer. Would be fun to see the pseudo “difficulty settings” on a wheel-on trainer at different great ratio choices.
Curious. How are you seeing wheel-on trainers being different? Do you mean a dumb wheel-on trainer or wheel-on smart trainer? If it is a smart trainer of any type, gear length of travel in inches is gear length in travel of inches (an absolute value) regardless whether it is direct or wheel on. So wheel-on and direct should have the same ratios (minus wheel slippage, of course).
If it’s a dumb trainer, your gear length is simply your available gear length (aka an 30×28 equates to 28.3 gear inches and 2.3 meter development while a 30×32 is 24.6 inches 2.1 meter development). It would be awesome if you could clarify, thanks so much.
Also important to note, gear spin at a certain cadence always equates to an exact minimum speed because of gear length. So if you spin a 700c/25 wheel with 172.5 cranks at 90rpm 30×28, you will be traveling at least 7.6 mph. (The reason I say exact minimum is theoretically you could be spinning as you coast down a hill and not engaging the freewheel; on a fixed gear bike you’d always be going exactly 7.6mph) But whether a 5% or 20% IRL, you’ll be going 7.6mph at that cadence and gearing.
This is good stuff, though now using my gravel bike (30-34 granny on the kickr core) I can just set it at 100% and forget it. Nice to have climbing gears even in the virtual world with Ven-top…
The chart mentioned above explained a different perspective i.e. gear equivalent for each TD settings at 10% gradient..
But lets look at it at a power output perspective, do you agree that for a rider ascending at a 5% gradient with 100%TD, will yield the same effort using the “Same Gear” if the same rider ascends at 10% gradient with 50%TD, maintaining an output of 200w and 80rpm??
Basically answering the ultimate question, whether the change on the % of a TD “virtually” (assuming a 10% grad):
(1) changes/decreases the Gradient (although the actual gradient will still be displayed) on the route
or
(2) simulates a higher ‘gear’ from the actual physical gear of the bike (connected to trainer) allowing a rider to climb from the “same gradient” with lesser effort
Thanks!
1 is the answer. It changes the gradient of the IRL bike to 1/2 that of the Virtual bike, but that will appear to be less resistance. However, the same watts/time must be generated to get your virtual rider to the top of the climb. This experiment was to show the equivalent GRANNY GEAR that my virtual rider would be on, on that 10% climb reduced to different difficulties (aka IRL being on a 5% climb using 50% difficulty. This was all about running out of gears experiment.
So I ran an IRL model of the numbers, b/c I am a nerd like that. Interesting that it wasn’t an exact 50%.
The 150 lbs. rider riding up a climb of 5 miles at 200w (no wind in equation.) would arrive at the top of:
5% climb at 34.8 minutes / average speed of 8.62 mph requiring 399 kJ / calories.
10% climb would arrive at the top at 62.59 minutes / avg speed of 4.79 mph requiring 717kJ / calories.
—————-
OR if we make ride time equivalent… say 60 minutes.
5% rider will cover 8.62 miles @ 200w
10% rider will cover 4.79 miles @ 200w
The 10% will rider will have gone +3% more than half the distance of 5%.
—————
Or if we make 5% half the watts (100w) of the 10% rider
5% climb time 66.12 min / 4.54 mph
10% climb time 124.07 /2.42 mph
So the 10% climb numbers aren’t exactly 50% of the 5% climb., rather 53%, slight advantage to the 10% climber.
Darn you! Its 321 am EST and I’m reading @ mathematical formulas and bikes. But I’m really here to thank you for using and posting Sheldon Brown’s gear calculator and just mentioning the beloved East Coast cycling legends name. Every couple of years I get stuck wandering around his archived pages online, and lament never meeting such an interesting and intelligent soul and cyclist. Thanks for the memories ! Great article! (I’ll read it again at noon w a few cups of Joe in me!)
.
Sheldon, may he RIP, was a legend. Even here in Texas we know that. 🙂 Another great tool is http://bikecalculator.com/
Fellow Sheldon-loving Texan here. That man was a real gem, and a kind soul to boot!
I’ve always explained this as a virtual front chain ring – as it does affect all gears.
I’ve still had to explain to my S/O about 20 times that it isn’t cheating!
It’s not “cheating” until your opponent runs out of gears. At that point, your ability to spin at a cadence that is physiologically more efficient than the poor rider out of gears and grinding at 30rpm is “kind of “cheating if your virtual gear is much beyond what you’d run IRL (aka a 77 rear virtual cog). ha!
Interesting article. But I’ll say this – regardless of how it works, I can climb alpe du Zwift a hell of a lot faster with trainer set to 20% than if it was 100%. It didn’t make much of a difference when I had a basic, wheel-on trainer but now I have a Kikr core it makes a huge difference. No question about it, if I’m racing against someone set at 100% and mine is set lower, I’ll have an advantage.
This is because you are able to stay at a cadence that is more physiologically efficient for you. You aren’t running out of gears. Keep going. Have you got the wheels yet? Somehow I did on the second attempt, but I hear people bemoaning that they have like 16 pairs of gloves. haha!
Great stuff. Thanks
Your solution only uses watts as a variable, but most riders play with TD so that climbs become comfortable. At that point they want to know how TD virtually changes their cassette, and what gearing would they need IRL to ascend a particular climb with the cadence used in Zwift. A generalized table can be created using a riders actual gearing at a specific TD and grade showing the virtual changes in their cassette as grade increases. This should be easy to program and am surprised it hasn’t been done already.
Actually speed is the real variable and how we reverse engineered the gearing because cadence at gear produces an absolute speed (caveat: except on descents where an 80 rpm cadence might not be engaging fully). So if I know the speed and cadence, I can equate the gear. (Just like if I know cadence and gearing, I can equate the speed.)
The equation calculation would be more complex than presented. Because the reduction in gradient fluctuates in a non-linear way on say Alpe because, while there is an average gradient (8.5%), there are moments of more 12% and less (reduced to 6% at 50% TD) and 7% (reduced to 3.5% at 50% TD). Since these are non-linear in the amount of extra gearing you get. Also, their KG would have to be fed into the equation.
This variant IRL affects the effort and strain of riding the route. If a 2% rise comes immediately after a short 2% descent, the rider can use the downhill momentum to “roll over” the following rise with reduced effort than if that same gradient was hit coming from an 8% section. (For the theoreticians, there’s an even deeper trickiness: the “fractal” perspective.)
You could get an approximation using average gradient, but it won’t be exact. You could also calculate it at maximum gradient to make sure you never run out of gears.
We did the experiment cadence at 80rpm b/c for most, that is a comfortable enough climbing cadence.
If you really want to nerd out, you can rearrange this formula: P = krMs + kaAsv2d+ giMs
Your article is focusing on experienced climbers getting efficiently up climbs with their preferred cadence. I was speaking to cyclists who do a big climb in Zwift and wonder if they could do a big climb IRL. The lowest gearing you use is 34/28 which is moves your rear wheel 1.21 rotations where many novice riders using TD setting under 50% would need a 1 X mtn bike gearing that allows gearing ratios under 1 to ascend IRL. The table I suggested would just give zwifters an awareness of the virtual gearing they are using.
Fantastic post. Really enjoyed reading it. And I agree with your end advice. Keep closer to real world settings if you want to climb in the real world. As I started reading I thought I should get away from default setting. Been up Alpe d Huez on 34/28 and was quite doable. Have the gearing on my bike on the trainer. Wtf. Loved the humor too. Lol.
Thanks so much. If we can’t be little funny and laugh at ourselves, what’s the point of living. #findjoy
“There is a lot of taxing on the muscular system at 50 RPMs cadence.”
Yeah – isn’t that the point?
I feel the point is to go as fast as possible as physiologically efficiently as possible so you can go that fast longer (or go even faster). The old adage holds true. It never gets easier, you just go faster.
Does anyone know:
Is the difficulty setting only effective on climbs? Or does it also change the behavior for descents?
I wonder, whether you could simulate higher gears on a low difficulty setting to still be able to pedal downhill (as the simulated gradient is lower), while at a higher difficulty setting (as the gradient is higher) you cannot spin fast enough to put pressure on the pedal.
Yes, it changes the descents too. If you are on 100% TD it can be very hard to keep up with people on 50% or less TD when descending, because you’re spinning out and they can push more watts against the extra resistance they’re feeling.
Good video on descending on Zwift here. It reduces the gradient of the descent to a degree, as well. Here is a solid article on that: https://zwiftinsider.com/trainer-difficulty-on-descents/
Thanks Jordan! Zwift changes my gearing because IRL I have the appropriate gears for a 650c wheelset. But that’s about 7.5% lower gearing than the same groupset on a 700c bike.
Zwift takes wheel size out of the equation because trainer difficulty assumes 700c because that’s the vast majority, so fair enough. It’s taken me a few years to realise this though! Trainer difficulty can help level that out. But it’s trial and error because I can’t work out what the realistic compensation amount is. I don’t think it is 92.5% (i.e. taking on 7.5%) and anyhow, that slider isn’t that accurate.
What trainer do you have?
A Wahoo Kickr, Gen 1
Zwift works on power, so wheel size is irrelevant to the trainer putting say a 200w load onto your bike.
If we used a wheel on trainer, we could ride Zwift and the trainer would put a 200w load on the roller whether we had a 650 or 700c wheel.
What we need to compensate for is the change in rollout gearing.
If we ride the wheel on trainer and our threshold wattage up a climb is 250w for our 650 wheel with a 34/28 gear combination, that same 250w with a 700c wheel will make that 34/28 gear combination feel harder and we will be going faster.
We need to add teeth to the cassette on our trainer as compared to what we run on our wheels so that we have the same effective bottom gear.
From this page: 650×23 = 1944 circumference and 700×23 = 2096 circumference
1944/2096 = 92.748%
If your cassette maxes at 28t then 28/92.748%= 30.189
If you chuck on a 30t cassette you should get close to your lowest available ‘on road’ gear compared to your trainer gear.
So I think change your trainer cassette rather than mucking with the slider, especially if trying to everest or anything (needs to be 100%).
Happy to be proven wrong!
Can you re-do this test with the Stages Bike using the Dream Gears?.. lol.. just kidding.. great article!
Sure. I’ll give you my address. Order it and ship it on over. I LOVE testing!
Curious. The numbers in the article do not correlate exactly to the “unmarked” slider position estimate percentages, ie 50% does not appear to give 50%, etc.
Practical experiment up Ventoux with a buddy this week. We rode adjacent all the way, no idea of bike gearing, same W/kg, same speed, 90 minutes duration.
Rider A: 90kg. Avg 240W, 2.7W/kg. TD 100%. Avg cadence 77
Rider B: 75kg. Avg 200W, 2.7W/kg. TD 30% Avg cadence 84
I expected much bigger differences in cadence, ie at “30%” I expected to feel 3x easier or have triple the cadence. Not the case. Seems 50% may not be 50%? Suspect the slider is like hot sauce, just forget the percentages and slide to taste 🙂
Maybe as a follow up, Jordan can plot the results on a graph to see how the “real feel” percentages/cadence correlates with slider position.
Good idea. Keep in mind that the gearing I showed was for ONLY a 10% segment of ADZ. Those ratios won’t hold true at 5%, or 8% or 12%. Ventoux sections vary in gradient. I want to repeat the experiment at 5% gradient to see what those numbers are, what gearing ratios are, power numbers are and compare them to 10% (Then maybe 15%). I am on KICKR Core so my difficulty caps out at 16%.
Paying no heed to the gear ratios is a huge flaw in your assumption.
As far as what you feel at the pedal due to the static (climbing) loads, the change in gearing is directly proportional to the change in grade. So going from 100% to 50% trainer difficulty is exactly the same as reducing the size of your chainring by 1/2 or doubling your rear sprocket. Exactly the same. Twenty five percent trainer difficulty equals four times larger sprocket, or 1/4 size chainring. One percent trainer difficulty equals 100 times larger sprocket, or 1/100th size chainring. That’s why it’s somewhat nonsensical to think about trainer difficulty in terms of gears when you get to the really low settings. But it is mathematically correct, at least as far a the static (climbing) loads are concerned. However, as you go to the low end of the trainer difficulty setting, you are trading static load for dynamic load. It is the load provided by your trainer in reaction to wheel speed and simulates wind resistance in real life. You are effectively riding a much longer distance at a much higher speed while your avatar labors up the virtual hill. It might help to sort that out if you were to try a similar experiment but instead of looking at speeds in the game, try counting pedal revolutions up a given section of hill.
New experiment idea. Will do. Revolutions for segment ADZ.
I believe the same effect on TD occurs when going down the Alpe. In other words a higher TD will make you go faster with less effort.
Yes, but there is an article here that shows it is not the same benefit in terms of gradient increase as it is in gradient reduction. Zwift reduced it so people won’t spin out going down the hill.
This is good but really just buy and put on the appropriate cassette in the first place and put at 100%.
I live in Texas. For IRL rides, there are no ADZ type climbs near me. A CAT 2 is 9 hours drive away. So IRL a 34×28 is fine and what I prefer. On those steep climbs on Zwift, I like have access to a 32. If I didn’t ride IRL, I would switch cassettes.
Thanks for this Jordan, very interesting article. I use a LifeCycle IC8 indoor trainer on Zwift and as such have no TD option. My gear changes is all done by the turn of the dial but it does simulate a very large gear range. Downfall is though that I have to be ready for the hills and manually crank up the dial to increase the watts otherwise I am dropped very quickly. Always wondered what kind of gear set I would have to run IRL to to simulate my usual Zwift riding.
Very useful article thanks. I use Zwift as a means of improving my outdoor riding so almost always ride at 100% TD because those are the gears that I’ve got outdoors and there’s some 20%+ slopes round here to get up! I don’t doubt that when I’m down towards 60rpm on the Alpe that it’s inefficient but I am improving, slowly!
The chart at the end is useful because it tells me that anything below 75% is beyond the gearing that I could realistically fit on my bike (without a major reworking of the drivetrain) so I’ll use that if I’m wanting to spin my legs a bit more.
Glad it helped! More tests coming!
Thanks for this article. I hadn’t really been aware of this setting, and certainly didn’t understand it. Changed to 100% difficulty because of article, and after getting used to having to change gears all the time found it a more real riding feel – ultimately my average power was exactly the same as my similar rides just before the change
Glad it helped. Your average power shouldn’t change unless you start running out of gears and find yourself spinning at a cadence that isn’t as efficient for you. Keep pedaling!
Does this ‘extend’ the gradient range trainers can do? Eg. My flux s tops out at 10%
With trainer difficulty at 50% will I feel the gradient increases in zwift all the way up to 20%?
Thanks Jordan for clarification. It is very useful and helpfu. I did Ventoux 100% and 10%. !00% was more demanding for legs but it was disaster to changing gears. 10% i could focus more to maintain power. So for ride for pleasure and for preparing for IRL mountains (as you mentionde) the higher difficulty the better. For racing it is better to use lower difficulty to keep in the pack instead of changing gears as sometimes there are less then sec and you are lost and race is over.
This article states that at 100% trainer difficulty you would feel the full 10% gradient and I could be wrong but I always thought Zwift halved any gradients therefore a 10% incline for example is actually 5% when the trainer difficulty is set to 100% and furthermore if you reduce your difficulty to say 50% then a 10% incline now is 5%
1/2 on descents only. Not on ascents/climbing.
Many people say that because by default your Zwift TD is at 50%. But if you move it to 100%, it’s true gradient on ascents.
I assume it would be just another calculation to do a different equivalency, to show the real life gear necessary to push the 311 Watts at 80 cadence for the lower trainer difficulty levels. I would find that interesting, and it might help to drive the point home to people that still don’t get it.
How does this transfer to non-controllable trainers such as an Elite Kura, where it’s a case of resistance being ‘controlled’ by gear selection?
It has no effect.
Can someone please help? I can’t get rid of this ‘5’ by my gears… does anyone know how to change this?
I did my first 35 rides or so on 50% because I didn’t know any better. I’ve changed it to 75% now for the foreseeable future because I don’t want the first hill to hit me like a sock full of wet sand to the face when I start riding IRL again!
Thing is though that when I lower my TD to 25%i never actually use my smallest gear because I’m not gonna spin like crazy. You should still be shifting into your ideal gear.
I think that the point is being missed here. All of what is said in the article is absolutely true. However! In actual practice nobody is going to leave their cassette in the same place after they change trainer difficulty. I like to run my TD at around 30% for two reasons. One, I’m not that powerful and appreciate more lower gears and Two, it means I don’t have to shift my gears as often or as far, especially racing. I hit a steepy in a race and one or two clicks (virtual) is all I need. If I was set at 100% I would have to shift 4 or 5 gears going from flat to 10% incline. On a relatively flat course with less than 5% changes in incline I rarely have to shift at all. So TD provides proper gearing on really steep stuff and is more convenient the rest of the time.