Fix physics simulation on the flat

I don’t have the faintest clue. Just looking at the R2 of these correlations is enough to say these are “very rough approximations”, and I don’t have the urge to go read the papers to see over which body weight and height range these were developed. I’d venture whichever one Zwift uses is being extrapolated way outside its development range.

Don’t forget also that all of these formulas put a much higher impact on height than mass. Everyone keeps harping at speed differences vs weight, and ignoring height.

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Yeah. Some of them have a frontal area proportional to height. You might be right about the range. These estimations are probably developed based on data for one kind of rider (adult man) and might not work as well for extra low (kids/woman) or extra high riders.

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Get a room nerds!

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With this knowledge in mind, I know exactly what to do as soon as they hide my height on ZwiftPower :wink::dash:


It was mentioned up above somewhere, but all these calculations (except for TT) have to account for the fact that draft is reduced in Zwift. That’s what their algo is tuned for.

(Please don’t take this as an endorsement of either the algorithm or the draft mechanics.)

The basis of discussion all the way to the initial post was for TTs. You are right in stating that drafting also plays a role in other cases, and that the model used is far from perfect.

Interesting enough, the initial argument included the common misconception that heavier riders “accumulate kinetic energy which means that less watts are needed to maintain said speed”.

I think what is meant by “accumulate kinetic energy” is that the kinetic energy can be converted to potential energy. If the ITT route is not totally flat, there will be a conversion to gravitational potential energy when going uphill and converted back to kinetic energy again when going downhill. This is why we try to have good speed when entering small hills, e.g. the Esses in Zwift, so we don’t lose too much kinetic energy (velocity) going up, and don’t have to apply much extra power.