Still waiting on an ultra light rider update

I’ve asked this repeatedly.

Is Zwift going to address the unusual game physics of ultra light riders anytime in the near future?

Here’s a stream including a supposed 37kg junior rider delivering a truly ludicrous performance.

The rider placed 3rd, a highly unlikely result at this bodyweight with appropriate real world physics.

Any chance @James_Zwift or @DavidP could look into it please?


Well, never mind ultra light, that was just nonsense. No one rides 6w/kg for an hour at a 135 average heart rate.

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Can you point out any specific timestamp?

Is Zwift going to address the unusual game physics of ultra light riders anytime in the near future?

What do you mean by “physics of ultra light riders”? The physics are the same for all! There is no specific formula for lightweight or heavy riders.

Now, if the user is lying about weight or have some sort of malfunctioning equipment that is another story.

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Zwift physics is broken for ultra-light riders. Their wattage, height and weight get translated into unfeasibly fast speeds in Zwift. Height is almost certainly very significant here.


I think this has been mentioned numerous times. The weight plus height combo appears to be some kind of magic bullet for speed on Zwift. If this had very little effect, then why would height and weight doping have been so prevalent in the past?



the original Zwift developers knew the formula had upper and lower limits where it became less accurate that is why we had a minimum weight setting of 55kg (i am 90% sure that was the weight)

But so many users complained and Zwift changed the lower limit and suddenly we saw why there was a lower limit.

My assumption (we know about assumptions) is the base formula was created and verified using pro and Cat 1 -2 racing cyclists that have a lot of data, as you move away from the average weight (i guess 75kg) you have less IRL data and it get harder to fit a formula.


I think it was 45, or 99 lbs.


You are correct @Mike_Rowe1 .

Not thinking clearly going up the Alpe. LOL


I am one of lifes naturally smaller riders, 165cm tall and around 61/62kg. My experiences of outdoor racing are fairly limited, but I have found that in Zwift races I appear to be far more competitive on the flat than in real life. However I have found that on the hills I lose the edge that I have riding outside.
I’m not sure whether this is down to the drafting effect or Zwift trying to balance things up, so that big and small riders can remain competitive in the various categories. I am pretty certain that I’m a better Zwift racer than my outdoor performances would show, even though my indoor and outdoor watts are just about identical.


I think the suggestion is that the physics model in use is less realistic for edge regions in both mass and height, rather than that there is a separate physics model based on mass.

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this is the average weight of a 10 or 11 year old boy… but I’m sure he’s legit :joy:

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I am currently 54.9 kg (48 years old, 168cm). I was 50 kg in my 20s. When I was a teenager (15-16 yo) I was something like 45kg…
Looking at his video, i’d say he is more than 34 kg. Weight cheating or just grew fast?
One of my sons went very fast from 40 to 50kg, he was already cycling, so he won everything in B for a few months (before getting more interested in partying, studying, biking irl with friends than zwifting)… he was always a little late on changing his weight (grew very fast and as he was exercising, he took a lot of muscle)

The video wasn’t taken by the 37kg rider; you’re looking at a different rider.

Oh! Sorry! :joy::man_facepalming:

Race summary at 1:06:20 showing 6w/kg average power for 60min at 134bpm heart rate average. Haha.

I thought the Zwift physics model worked until 45 kg.
Riders under 45 kg would start to have altered game mechanics.
Kind of like using ZP instead of a power meter.

Let them ride and do workouts but not race.

Ultimately, the game needs to be fixed or place some boundary limits.
These light riders are not cheating.
We actually want to encourage them but let’s not give them participation trophies because of poor game physics.


But some might be. Why not just remove the temptation?

Imagine the result if avg HR was up closer to a junior’s typical Z3 or Z4 (~150?)

Is the physics really broken if the kid does 6w/kg at 223w and still only finishes 3rd?

223w isn’t a shabby number (plenty of people in that race who had less). If the physics was broken then they should have smashed the field with that w/kg.

I think the real question here is how is someone who weighs only 37kg and has a BMI that would be classed as severely anorexic capable of producing 223w for an hour? Double arm amputee maybe?