Zwift is not fair to lighter riders


I have said it before and I said it again.

No one ever said that the same w/kg should go at exactly the same speed. It is an easy way to compare to compare effort between different riders. There is a lot more to play on steeper hills the heavy rider will need more watt.

People are to focused on w/kg.

The zwift equation does not use w/kg to calculate speed it uses weight, power , length and all the terrain parameters. Yes watt and kg is in there but not as a w/kg term.


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So you can see in the formula above where Power § and weight (Frg) is used.

I assume Zwift use a simular equation.


I think allmost all will know this, I certainly do. But you refering to the static computation while I am interested in the dynamic behaviour, since it seems the magic goes over there.

Yes @AlexanderPerdon, bigger riders will produce more watts, but they will also go slower on the hills. That is why IRL climbers is small and light but track cyclist are big guys.

The Track is a long flat road so your weight is not against you.

There is a reason why track cyclist weight more the Climbers.

robert-foerstemann 96kg

Chris Froom 68kg


@AlexanderPerdon: By dynamic do you refer to acceleration. You can test this. Change your weight to 100kg and see how long it take to go from 0km/h to 40 km/h then try it at your current weight.

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Yes, but how to simulate pushing more raw wattage :wink:

Anyway, I will get some problems at ZP when I play around with my weight. I don’t want to risk DQ just to verify this.

ZP wont care if it is not a race.

So to add to my argument ZP Top ranking racer.

1st Stevie Young 78kg
2nd Adam Zimmerman 57.2kg
3rd Greg Leo 59.9kg

If Zwift was not fair the the light riders then the top 10 would all be 100kg riders.


I know there’s often discussion about a rider’s ability to output power on a trainer as opposed to a ‘real’ ride, but I do know that if I try to use my real world FTP as a basis for any trainer-based training it’s a waste of time, I’m wrecked before I’m even half way through a session. I don’t mean the measurement of my power output is wrong, I just mean I can’t output as much sustained power on a trainer as I can on the road, be it due to lack of cooling, rigid position, different muscle usage – there are many theories.

The bottom line though is that I reckon my trainer FTP is probably at least 15% less than my road one, though maybe a bit less by spring after a winter in the garage. I never seem to be able to get the value right on trainer training programs though!

There’s a great article on why outdoor and indoor FTP are likely to be different (generally indoor FTP will be lower indoor):

People who race in Zwift usually have the trainer difficulty setting set anywhere from 0% to 30%. There are smaller A racers like PDF (the Poison Dart Frog) who weigh very little and often work as domestiques and can crush larger riders on the hills and even on the flats. Watch some of the Zwift Community Live races and see how well light riders can do. The constant attacks make me exhausted just watching them.

That being said, I know Zwift is also working on a new draft algorithm for races so maybe you will find some advantage for lighter riders if you can try that out. From what I seen it make it a lot harder to break away from the group, but it is a work in progress.

Try to play with that calculator, it shows pretty weird results when it comes to higher wattages, just as any other calculator available online (try to calculate how much watts Wiggins would need to set his hour record lol). And even on lower wattages, those calculations are quite off from real world numbers you would get riding on empty indoors velodrome.

I know we already discussed that in the topic I made some time ago, yet something works wrong here, I can guess that calculations are simplified in Zwift, because there is already so much data processed in real time. But I think that in the end that is not important, since this is just a game, and no clue this is the best cycling game available out there.

Anyway, I think physics of Zwift will get better with time just as any other feature of that product.

440 watts. Using the calculator as is, I came up with more like 500 watts. But apparently the best in the world can make 440 watts do the speed that the rest of us might need 500 watts to accomplish. The radio buttons on that calculator do not have choices for the world’s best bike tech, the world’s best coaches and fitting and training and a TdF and Olympic track champion. Those calculators apply better to average riders in average positions on average bike tech.

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0-30% would indeed explain some why some other rides seem to have advantage on “flat” and rollercoast-type of road. Simply because they are able to continue their wattage for a longer period.

@nvm I can indeed remember that I read a topic a while ago. But to see it in practice makes it real to me. Yesterday I also had this strange experience that while pushing 0,5-1 watt/kg more on a 7-10% hill in London, it took far longer than IRL to overtake the other (heavier) rider just because he was pushing more watts than me.

@AlexanderPerdon: It is not set in stone that if 2 riders of different weight doing the same w/kg will go up a climb at the same speed. w/kg is a rough estimate to compare riders. Look at the formula I posted there is a lot more involved than w/kg. w/kg is not even in the equation.


I know that and I never claimed that 2 riders of different weight doing the same w/kg will go up at the same speed. That is mainly because of the bike which is more or less the same for both riders and relative more heavy for the lighter rider.

However, if you would calculate the speed using 6kg bike for a 60kg and 8kg bike for an 80kg rider, you will notice that a climb of at least 7% the difference in speed is quite small. So yes in the end the speed within the formula is completely w/kg based. Only because of pratical reaons (allmost same bike weight) the lighter rider has a disadvantage. But that I am total aware of and it is acceptable. But in Zwift it seems there is more “magic” around this.

Just put 20 pounds weights around your waist and then make yourself 20 pounds heavier in the game and problem solved. You will weigh like everyone else.


Bicycling mag did an article in the early 90s that came to the same conclusion Zwift does…i.e. if we define a cyclist’s fitness as watt/kg then a heavier rider at same fitness level has an advantage (most on downhill, moderate on flats, slight when climbing).

This is a fine starting point for Zwift dynamics, and should be reflected in solo riding. However, in drafting situations I think Zwift assumptions break down. (My understanding is that zwift gives an equal percentage “break” to all riders drafting so a lighter rider has to do higher w/kg than a heavier rider to stay in the field).

I think where that misses mimicking the real world is twofold:

  1. Smaller riders (correlated with weight) benefit disproportionately from drafting vs. larger riders. Zwift does account for height but I think this drafting benefit disparity is not expressed sufficiently in Zwift.

  2. Steady state vs. constant mini accelerations. A solo effort will definitely favor a heavy rider but riding in a field IRL is comprised of continuous mini efforts resulting from the need to accelerate/decelerate constantly. IRL this tends to favor a lighter rider. In Zwift the effort in a field is often just a steady hard effort and your avatar moves right through people forward and back as a reflection of effort. It’s more like a giant group TT.


@Derek_Brauch Great post, you have some valid points here.

I want to add that I have a strong feeling something really goes wrong with the draft effect with the result that a group goes faster and faster and far beyond the speed as being pushed in wattage by the front riders. This is because riders just overtake eachother and while in draft you still can push high wattages while IRL the resistance will be far lower. The riders with higher FTP will benifit the most from this.

Yes there is a slingshot effect resulting from the drafting that launches riders to the front on a continual basis that is not present IRL. IRL when you get a run on the rider(s) in front of you you stop pedaling as there isn’t a physical path to the front (or, often, a desire).

I try soft pedaling when I get near the front but I usually end up at the front anyway which then kills my momentum and I subsequently get shot to the back suffering the opposite effect.

All of this said I think Zwift is a tremendous program and has allowed me to continue to ride whereas time constraints had knocked me out of the sport last year.

I still would like to see a Zwift crit course with zero power zones in the corners.



No need to try being a 90kg rider. That’s my every ride! LOL

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That made me burst out laughing.