I feel that Zwift should do some actual real world testing, the heavier rider doesn’t have to produce way more actual power than the lighter rider on the flat to achieve the same speed. Sure the aero is a little worse but nowhere near the level that Zwift currently pings you for being heavy.
A 60Kg rider and a 100Kg rider both doing say 2.5W/Kg are NOT going the same speed on the flat, sorry but the heavier rider is faster. Identical bikes if the 60Kg rider is doing say 30km/hr the heavier rider is closer to 35km/hr on the same 2.5W/kg, there is no way the higher drag coefficient cancels out the entire 100W difference at this speed. Once in the identical draft its only going to start making the speed difference greater.
Sure on hills its nasty its all W/Kg and when the speed drops to like 6Km/hr you can completely forget about drafting effects and any difference in drag coefficients. The real world heavy rider has to produce only slightly less W/Kg to stay level due to the bike weight being less of an overall percentage difference.
A change could be made to the Zwift HUD, instead of W/Kg on the flat, change to power, when you hit the 1% incline or above swap it back to W/Kg and for anything downhill it really needs to be power as well, the heavier rider is faster and this helps offset the drag difference.
Really only thinking of this from an improvement to Zwift overall otherwise basically heavier riders are going to just say stuff it and subtract 20Kg from their rider weight to compensate. I guess the argument could be that you “fix” the problem only to have them drop 20Kg anyway, at which point all the light riders will really start screaming. There is no ultimate solution to the problem until Zwift actively weighs the bike and the rider during the whole ride.
Sure its a complex calculation, I appreciate that Zwift has worked on it for years, for example the heavier rider has more inertia for short steep climbs after a steep decent, its great but overall I think Zwift disadvantages heavier riders which then just encourages weight doping.
Anyway just my 2 cents worth after 3+ years on Zwift.
I’m not saying you’re entirely wrong, but looking at the issue from the other end …
Go ask a 55kg woman doing a 2.5wkg group ride if she’s doing 2.5wkg to keep with an 80kg avg weight group doing 2.5wkg on Tempus Fugit.
She’ll fix you with a steely gaze, I suspect.
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And what percentage of women riding on Zwift are actually 55Kg ?
Just out of interest today I Googled the average weight of men in the USA, would you believe it the average ago of men in the USA over the age of 20 is 90Kg.
The average weight of Women is 77.5Kg. I’m pretty sure if Zwift crunched the numbers not even the average weight for men would be this low.
The rider dynamics is either based on Physics or its not. You are never going to please everyone but if you have to keep changing it all it proves is it was never right in the fist place.
Any chance the average weight of men and women who exercise regularly is less than the average weight of the population ?
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Sure. Let’s have this (also from Google)
Approximately 40-42% of U.S. adults are considered to have obesity
as our baseline.
Really?
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You are correct and that’s how zwift works the heavier rider will be doing less w/kg to keep at the pace.
In your example of 100kg rider doing 2.5 w/kg i reckon the 60kg rider will have to be doing about 2.7-8 ish to stay at the same pace.
Check some iTT results will back this up.
When googling average weight and attempting to apply it across the globe, using the US as the benchmark might not be the most accurate way to do it.
It’s probably a bit more accurate to generally look for the average weight of a recreational cyclist globally, which is probably a bit less heavy than the average US population weight.
That said, I also believe your main point is true, and that is… people on Zwift are on average lower than their real world weight. So the average Zwifter is likely lighter than the average recreational cyclist as a result.
And a good many of them are probably lighter due to misrepresenting actual weight.
I know for years my weight was not changed in game, even after my heart attack and losing over 30 pounds. I was doing myself a disservice by not adjusting my weight in game to my actual weight.
But for many, as has been speculated, the opposite is true. Many Zwifters are underreporting their actual weight to gain an advantage in game.
Yeah, I imagine that is true. I think there are a few folks who set their weight and forget it (then gain weight and never go back and change it), but probably many folks who are ‘somewhat aspirational’ when they set their weight - meaning they are either purposefully setting a lower weight, or are kidding themselves, using a weight they had in high school, and not checking it on a scale 
I do weigh myself every day after I shower. I fluctuate 2-3 pounds, and have for years.
I don’t go into the Zwift settings often, maybe once every 3 or 4 months, so my weight in game is almost never what I weighed that day.
But, 2-3 pounds won’t matter that much for someone like me who is not trying to be competitive in races.
The average weight for men in the USA aged 20 and over is approximately 199.8 pounds (about 90.6 kg), according to data from the Centers for Disease Control and Prevention (CDC). This average corresponds to an average height of 5 feet 9 inches (69 inches) and reflects a trend of increasing weight over the past few decades.
That has nothing to do with the population on Zwift. I don’t doubt it’s true for the US as a whole. The question you are asking is completely unanswerable for two reasons. First, Zwift knows the reported weights of riders and they won’t tell you anything about that. Second, reported weights are not actual weights and even Zwift doesn’t know how they differ. Zwift does not know the weights of their users.
Bell curve, its going to be offset by the number of people joining Zwift for the sole purpose of weight loss. Sure if you move up the categories and focus on racing only then the average weights will begin to decline.
This whole thread is, I fear, based on the misconception that speed on flat roads in Zwift is largely or wholly proportional to watts per kg.
It isn’t. It’s largely proportional to raw watts.
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I imagine it might be slightly offset - but any chance it will STILL be less and to the left of the general population weight bell curve?
Correct, less a bit of difference in the drag coefficient roughly based on height and weight, which on identical bikes in Zwift would be negligible. The lighter guys would be getting wasted on the flats so if you throw in short course flat racing its no different to 100M running and marathon running, or velodrome vs road, your physique determines the winner its just pure raw Watts on the flat.
So what do you want to change and why? I’m lost now. 
Change to HUD right hand side from W/kg to just W on the flat. The W/kg is masking the problem in making you think you need to do the same W/kg as the lighter guys for the same speed.
It sounds like you may be a assuming there is a universal constant for the gradient at which this changes, but it varies by speed, which means a low power rider like yourself will switch from Watts to W/kg at a modest gradient, but a fast rider (or someone working harder) will get into much steeper territory before that happens because speed will remain high. There are riders who can draft their way up the Alpe in a TTT. Maybe there is an elegant way to handle that but it sounds complicated. My guess is there is no chance of this happening.