I’m not sure where any comment I made would make you think I thought differently here. They have to model CdA as some function of weight and height. I have no idea what assumptions they make in terms of CdA based on weight and height.
That said if they model dynamics via any method I’ve seen, watts and whatever CdA assumptions they make are going to be the most important factor when on flats, w/kg will be the most important factor on steep climbs.
good luck with your hypothesis. whatever it is
Thanks, it’s in the title 
i mean your actual hypothesis, once you figure out what that actually is. because the topic of “light people have it easy” or “heavy people have it easy” for that matter too, shows up on these forums about twice a week
If they model CdA as a linear function of weight (and ignore height completely) then it immediately follows that w/kg is the determinant of speed on the flat. That’s just elementary maths.
(They don’t actually do this of course. But my point serves to refute your claim.)
“He who refuses to do arithmetic is doomed to talk nonsense.”
I’m still not sure what you are refuting.
The A is frontal surface area, which scales allometrically (disproportional) as a function of volume. In scientific literature, CDA is proportional to weight to the power of 1/3, meaning the bigger you are, the lower your relative surface area. What I suspect is that zwift uses a higher scaling coefficient (more like 0.8-ish),
Which means cda scales too linear w.r.t weight
my point is that watts / CdA is W/kg if CdA is modelled as a particular form of weight. So saying one matters more than the other is gibberish. It’s like saying the volume of a brick matters more than its length, breadth and height in determining its weight.
Zwift also explicitly uses height. It’s certainly debatable how good its formula is, but the silly claim that speed on the flat shouldn’t depend on weight (made repeatedly by Gerrie, as he does again just above) is tedious and wrong.
I don’t understand that perspective. Can you link to any model that says w/kg is a good way to predict speed on flat surfaces? We’re not talking about linear models, so what you will see is it’s better to talk about raw power and CdA, where there isn’t a linear relation between weight and CdA in general.
If you can measure CdA of course there’s no reason to use weight. But equally, if you can’t measure CdA then you have to estimate it somehow.
I mean, obviously zwift does use CdA in its physics - that’s part of how bicycle speed is calculated. But the value they use is a model that depends on weight and height because that’s the only relevant data they have to estimate it.
It’s a bit oversimplified, because weight influences rolling resistance and also indirecty CDA because weight has a volume and cosequently a surface area. But it’s at least approximately true that raw watts should be the main predictor.
Nice, now we’re talking! How do you post links btw? I’m somehow not allowed to
Well, the essence of it all is that CdA is in reality not even close to linear w.r.t. weight…
The more mass you have, the lower your surface-area-to-volume ratio.
