Speed is roughly accurate in game, based on the obvious limitations (they can’t model for wind, changeable body position, etc). But versus BestBikeSplit it comes up accurate across different course profiles.
The drafting is far less accurate though (You actually have to work harder to stay in the draft versus real life).
In real life, on the flat, someone doing 3 w/kg at 200w sat behind someone doing 3 w/kg 300 would stay in their draft easily.
I was under the impression that this was by design,
i.e. that the “double draft” event setting was the more realistic one and the default earlier on, but racers didn’t like it and the drafting was pegged back. Though someone who was around in the early Zwift days may well say that’s not correct.
That’s not what I am talking about though. Both riders in the draft of the group (same air resistance they face if they are the same height), both have the same w/kg, does 60W less power translate into less speed or not? I’d like to see a zwift simulation of this. There should be about ~3 km/h speed difference, but I don’t think that’s the case in zwift.
How did you get to 3km/h?
bikecalculator:
Enter 7kg for bike weight, enter 180w and 60kg, you get 30.85 kph, enter 240W and 80kg you get 33.81 kph. So, everything else the same, lighter rider with 60W less power should go ~3kph slower.
But that is not in a group. In a group there is less drag. So rolling resistance and slope of road will play a bigger role, thus the heavy guy need to work harder.
If both riders are in the draft of the group, can’t we assume that they face the same drag, especially if rider height is constant?
Yes but it will be much lower than in the calculation (the calculation assume a single rider) thus having a smaller effect.
No. Rider drag is affected by both height AND weight. Skinny people are more aerodynamic than fat people.
I think that really depends on where you have your weight. Most of the drag is due to frontal area, so it’s not unreasonable that someone with more weight can have similar frontal area as someone who weighs less. Obviously Zwift needs to make simplifying assumptions here. Let’s not forget that heavier rider will also have more rolling resistance. Not sure if that’s how it works in Zwift though.
I’ve often wondered whether a lighter flat fronted rider might be less aerodynamic than a heavier but “rounder” rider if their widths are similar.
That was my impression too. Zwift is not designed as a hyper-realistic cycling simulator, it is designed to make indoor training more interesting (and as realistic as possible with that proviso).
Ergo, making the draft less advantageous forces you to work a bit harder … which is, essentially, the point of training.
Theoretically, yes. Same frontal area (A), different drag coefficient (Cd), yielding a different CdA. Assuming the rounded rider is a cylinder and his flat colleague a flat plate, the former would be way faster than the latter at same power.
But none of this exists in Zwift, as the aero model is based on height and weight only.
Clearly the optimization would be a person with golf ball like dimples… 
UCI have already thought of this, and banned it: ::
It can’t be both “designed to be interesting” and “as realistic as possible”. Even with that proviso.
Ironically, making the draft less realistic has probably had the opposite effect and made racing more predictable and less interesting.
I am pretty sure you have misunderstood what I meant.
Zwift’s stated goal from the outset was to make indoor training more interesting than it had been up to that point … i.e. throwing on some music or the TV and staring at the wall while spinning on the turbo trainer, or looking at your workout intervals on a training app.
It has never set out to be an ultra realistic cycling simulator, but tehy clearly wanted to make it as realistic as it could be given the focus was on making the experience of indoor training likewise as interesting as possible.
They didn’t even initially set out to make it a racing platform, that was a response to the fact that so many users were using it for racing anyway, it made sense to formalise it in some way. The unsatisfactory nature of the classification system is likely born of the fact that it was not intended from the start.
You’re both right.
Hope you did so many tests with your lighter friend riding paired, so you can have a proper knowledgement about what happens IRL facing de wind… 
It’s true about the draft, but riding alone like in ITTs still making taller and heavier way too much slower than IRL…
Well, after hundreds of races I never have seen a breakaway!
Only a certain number of best quality riders (10-15? with a proper relief work) can achieve some kind of cuts away from de pelotons.
It can be casual.