Does ZWIFT have an AGE or GENDER bias?

A relative of mine just opened a zwift account for me so that I could train on his wahoo kickr,
I put in all my personal data - I’m female, 18yo, just under 5’, 101 lb.
I was riding the TT bike on level ground, maintaining between 2.6 & 2.8 w/kg.
Then a rider (male, from the avatar) PASSES me and he’s doing ~2.0 w/kg while passing me and he maintains that while pulling ahead!
Later, another (male) rider, on a TT bike pulls level with me and stays there for over a minute, while putting out ~ 1.6 - 1.8 w/kg, while I’m doing a steady 2.2 - 2.4 w/kg.

From everything I understand about zwift, this should not be possible. I believe that speed is based on power output in w/kg, so 2 riders on the same bike and road having equal w/kg power output should be going at the same speed.
I’m on the short side, so I don’t think my height had anything to do with it.

Is there something that I do not understand here?
Could someone please explain why this happened, or is it a ‘bug’ in zwift ?

Thank you.

On flat roads, raw power has a larger impact than power to weight ratio.

See for one example calculator. e.g. a 100lb (45kg) rider at 112W (2.5w/kg) might be riding at 26kph. A 200lb (90kg) rider at 180W (2W/kg) would be doing 30kph.

Once you start going up gradients, power to weight ratio becomes more important, and your assertion that two people riding at the same power-to-weight should ride at the same speed becomes more accurate.

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It must be a newly discovered flaw, that Zwift is now checking people’s ages and handicapping them appropriately. :thinking:

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Only up a reasonable incline. On the flats, what that w/kg equates to in actual watts is much more significant. So if you’re doing 2.0w/kg, at your weight that’s roughly 90W. Someone weighing 75kg also at 2.0w/kg will be doing 150W. Chances are they’ll be taller than you, which slows them down somewhat, but they’ll appear to fly past you.


Also a bit of info here: How Does Zwift Calculate Rider Speed? | Zwift Insider


Oh… really ? OK, maybe that’s it!
Thank you … we’ll think about that and try and do the math - try and ‘get our heads aroung that’.
Thanks again.

Thank you. OK, I think I am beginning to understand .
We both thought from what we’ve read and seen on youtube that ‘watts/kg’ was the major factor controlling speed, with height (aero) having a small effect.
Thank you again.

I posted this question to zwift support, and they said that they would get back to me with an answer. Let’s see what they say :slight_smile:

Thank you for replying.

I guess from what you are all telling me, I’m just going to have to ‘muscle up’, and generate more power in order to keep up. Hope my power goes up faster than my weight :slight_smile:
Thank you again for all your advice.

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I would guess that when comparing yourself to physically stronger riders, you’ll probably find yourself more competitive on the hills. But in general, focus on your own improvements rather than what everyone else is doing.

Unless you’re racing, in which case you need

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Actually, you are correct, I do seem to catch and pass a lot of the riders that passed me on the flats when the gradient gets above 4-5%. (I give them ‘ride-ons’ as I go by :slight_smile:


Also, TT bikes don’t get the draft benefit, putting you at more of a disadvantage if other riders are pulling past you in a bunch.

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It’s really more of a weight bias than a gender bias. I’m closer in weight to a typical woman than a man. In real-life races, I’m competitive, but in Zwift races, I get beat by riders a full classification lower than me, who outweigh me by 100 pounds, just because they have 30 more watts on tap than I do. At 101 pounds, you are a featherweight, so the bias is going to be even more pronounced. And even in real life riding, on flat terrain, bigger and more powerful riders will have the advantage over you, since wattage as an absolute number is more important than wattage per kilogram. In general, Zwift doesn’t penalize weight as much as riding in real life does. The climbs don’t hurt as much, regardless of weight, but on the flats, the draft effect is much less noticeable, which works against lighter riders.

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Even going up steep hills on Zwift, a heavier rider will go somewhat faster than a lighter rider at the exact same watt/kg power output. I believe this was demonstrated on the Box Hill climb a GCN Youtube video.

Thank you. From watching some youtube videos we got the impression that ‘w/kg directly determines your speed’, so I was surprised to see riders with lower w/kg values passing me on the flats, as it seemed to contradict what had been said. I suppose that the only people who really know the relationship between w/kg and speed are the programmers at zwift.
And they can change their algorithms at any time.
So, just with American Muscle Cars, ‘Nothing Beats Raw Horsepower’ :slight_smile:

OK, but I do seem to catch quite a few riders on steep climbs who had passed me earlier on the flats. :slight_smile:

also, if it’s just a free ride, there may be people around you riding in group meetups with “keep us together” switched on, which means their wkg will not correlate with their speed at all.

unless it’s happening in events, i wouldn’t worry about it.

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That’s true heavy riders have a hard time going up hill especially if the grade is more than 5%.

Play to your strength and make them hurt on the climbs.