Fix physics simulation on the flat

It is well known that on flat terrain the importance of the rider’s weight, and therefore the w/kg ratio, loses much relevance, as gravity is not as determining a factor as in climbing.
In fact, the main forces to overcome are aerodynamics and rolling resistance.
Even at certain speeds (40km/h or more) the rider’s weight favors inertia, which supposes an accumulation of kinetic energy that means that less watts are needed to maintain said speed than if the rider is lighter and has less inertia.

This morning I witnessed a ridiculous and unrealistic fact regarding “simulation”.
Someone with a weight of 63kg and pushing 329W (180cm height, so no “aero” CdA advantage) has won by almost 2 minutes difference VS two professional cyclists, one of them weighing 81kg and pushing 393W in the ITT developed on completely flat terrain such as Tempus Fugit.
Anyone with minimal knowledge of cycling can know that in real circumstances, the professional pushing 64W more on the flat and weighing 20kg more, it is normal to beat the light rider by at least 3 minutes.

We know that many people love climbing and for them cycling is just that, but the reality is that not everything is climbing in cycling and we would like some realism in terms of simulation on flat terrain.
There are many physical-mathematical models and data in bibliography to predict behaviors in this field, and if the Zwift team does not know them or cannot obtain them, which is highly unlikely, surely some of us can provide them.

Thanks for your attention.

What bikes and wheel sets were the riders using?

…exactly same, as today we all rode with the 80’s :sweat_smile:

In any case, such differences won’t be explained by aero specs of frames and wheels… as Zwift people know for sure.

Aero frames and wheels can make a difference.

But does it really matter?

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yes, as Zwiftinsider guys proved, best aero wheels+best aero frames VS the worse frame+wheels would be around 40-50 seconds on the same Tempus Fugit route in a 2900-3000 seconds duration test.

That’s not the point, I’m sure.

I think it’s about using w/kg to predict speeds on the flats quite like if they were hills.

Even if Zwift fix this, people maybe stop to put 20kg less than their real weight in the profile :smirk: :joy:

What race was this, Can you share the Zwift power link.

How tall is the pro?

Zwift dont use w/kg to determine speed, Zwift use power W and many other factors like cda, weight ect.

On Tempus Fugit there are inclines and declines that have an impact on speed. I ride it all the time and I see the differences when doing steady watts, speeds can swing from 18mph to 26mph.

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This was the event, altough the pro’s are not listed:

See first and second:
1st, time: 22:47–> 327W 61.0kg 173cm
2nd, time: 23:20–> 329W 63.0kg 180cm

Professionals were: —> 8th, time:24:32 @347W and 73kg —> 9th, time: 24:34 @393W and 81kg
3rd One day race European Continental Championships - ITT ('19)

what a joke! :joy:

In my experience… @300W I was moving between 38-41kph… :face_with_raised_eyebrow:
I remember to see around +/-1% slopes only…
Note this:

  • Distance
  • Elevation

The guy in 1st 61kg 173cm tall
Pro in 8th 81.7kg 190cm tall

The pro is a lot taller than #1 thus the cd value is a lot higher.

1st place: 43.9km/h 24min 42.5sec

8th place: 42.4km/h 25min 28.3sec

This was done on a perfectly flat road, times will be slower for the heavy rider if they go up.
Thanks to

did you see the bike the winner used?


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Well you did a mistake, 8th pushed 393watts! —> so predicts 44.7km/h speed :wink:

But no problem… What I think is…Oh my God !!!

Really? :smirk: :joy:

Do you think that if a rider is 17cm tall, then his CdA is much worse to explain he is 1 minute and 47 seconds slower in a flat ??

Well, nobody can believe that in the real world …

I’m really sorry for the short and light people on Zwift, but … reality would be very disappointng, so don’t try it in a real ITT outdoors … :slightly_smiling_face:


1st–> 173cm 61kg, speed: 43,7km/h, time: 24:43
2nd–> 180cm 63kg, speed: 43,5km/h , time: 24:50
8nd–> 190cm 81kg, speed: 44,7km/h, time 24:10

Maybe still not as the real life, but more accurate for sure than:
1st, time: 22:47 speed–>46,9 km/h!!!
2nd, time: 23:20 speed–> 45,8 km/h
8nd, time: 24:34 speed–>43,5 km/h

As we see at Zwift :wink:

You are assuming that they maintained the same watts during the entire event, which I am guessing is not the case. I think it makes a difference WHEN and HOW you use the watts and also how much the watts fluctuate during the ride.


Are you serious? Really?

Well, then every short and light rider that are able to push 330W can beat most of the best pro timetrialists… :roll_eyes: :joy: :joy:

No way, man.
Please ask somebody experienced and involved in some real life cycling data

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I am not kidding and have been riding IRL and on Zwift for a long time and I know fluctuations in watts can make a huge difference.

It’s not about the average.

No I did not.

My arm is longer than 17cm?

YES, you did! :joy:
If you read again, I SAID that the pro’s were NOT listed in Zwiftpower, so I posted their data as I saw in Zwift Companion classification! :wink:

Ok, my bad. (who is not on ZP?)

Where do you get the pro’s height and weight?

You also need to consider that they are not riding at a constant power, the smart rider will produce significantly more power on the inclines.

You are still just working off of averages (watts and speed) and that is not giving you the correct or entire picture of what happened.

That’s the fastest TT setup possible, if the other person was on stock zwift tt or basically any different bike and wheels and they’re at a disadvantage vs the winner