Zipp High Desert Speed Challenge

And to add to that I would be surprised if Zwift look at your weight to calculate your CdA (frontal area) together with your length. the reason I think so is because a 6ft 200lb rider will have a larger CdA (area) than a 6ft 120lb rider.

nope, being heavy does mean you also have a bigger frontal area. And remember you still have to accelerate more mass.

Edit: I found the formula.

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Using the calculator provided above, a 175 cm 85 kg rider has a CdA 6.5% greater than a 170 cm 70 kg rider. If the smaller rider is putting out 250 watts, the bigger rider should match their speed at 266.5 watts. So on a flat road 16.5 watts should make up the difference. I’ll buy that.

I’m averaging 290 watts and getting beaten by smaller riders putting out 250 watts. That’s a 40 watt difference. Doesn’t seem right.

Maybe I just suck at racing. I’d prefer not to think so. And in most of these group rides it would be difficult not to be in the draft 99.9% of the time so I don’t think tactics can explain the difference.

For sure there are some other variables in a group ride. Perhaps someone with an ANT+ simulator will run some experiments on Fuego Flats.

Control: 170 cm, 70 kg, 250 watts
Test 1: 170 cm, 85 kg, 250 watts (What’s the time difference?)
Test 2: 170 cm, 85 kg, 263 watts (Does that equalize the times?)
Test 3: 175 cm, 85 kg, 266 watts (Add 5 cm, is the time the same?)

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There is some tactic in these TT events, this route has that little climb in the middle 2% at the waterfall. So there the lighter rider will also have a bit of advantage. I saw people lose a lot of speed going up that little climb if they just keep there power constant, you have to attack that bump.

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Well, I own an ANT+ simulator; I’ll try to come back with some results, but I tell you, is not that simple.

We’re able, as unprivileged users, to only set up a time-based workout. Unfortunately with a time-based workout, else if on a given route, like say Fuego Flats, you cannot be sure that your ride will always start on the same point. Actually, the ride will mostly start on a random position relative to an arc. That means the inbound chronometer is useless and you need an outbound chronometer.

I lately fired up some tests on performances, for my own weight and height and FTP, of the Tron bike against Venge + Super9.

Results look like skewed and not repeatable. As an example, with the Tron, I have a full Watopia Climb loop ranging from 35’55" to 36’01"

This is to say I don’t really trust my own test platform. But who knows, maybe I’ll learn something in the way.


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That would be great!

I don’t know the limitations of the ANT+ simulator… Can you set-up a workout so that it includes the 7 km Fuego Flats timed “sprint”? Or use (or create) a Strava segment?

I’ll do my best. More later.

But I repeat, we can’t have distance or segments based workout on Zwift, at least as an unprivileged user.

So what I’m going to do is: start on Tempus Fugit; wait for the sprint finish line and then take a screenshot; complete one whole turn and take a screenshot.

The bike will be Zwift TT with 808/Super9.


Why would you need a distance based workout on Zwift? Workouts on Zwift SHOULD be time/watt based.

You could also do a search and vote up the request for creating manual laps within Zwift.

Also, lets keep this thread on topic.

:confused: A 6’4" rider weighing 200lbs has a larger frontal drag than a 5’4" rider weighing 200lbs?


6’4" rider weighing 200lbs TT CdA= 0.267

5’4" rider weighing 200lbs TT CdA = 0.2399

I don’t believe that if the riders are holding a good TT position.

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That is what I found in the Literature. Zwift may use something different that I don’t know. The certainly did not do wind tunnel tests. :slight_smile:

Lead in Finish Line Lap Time
Control: 170 cm, 70 kg, 250 watts 03:44,0 29:18,0 25:34,0
Control: 170 cm, 70 kg, 250 watts 03:44,0 29:19,0 25:35,0
Control: 170 cm, 70 kg, 250 watts 03:41,0 29:14,0 25:33,0
Control: 170 cm, 70 kg, 250 watts 29:14,0 54:49,0 25:35,0
Test 1: 170 cm, 85 kg, 250 watts 03:58,0 30:40,0 26:42,0
Test 1: 170 cm, 85 kg, 250 watts 03:54,0 30:34,0 26:40,0
Test 1: 170 cm, 85 kg, 250 watts 30:34,0 57:13,0 26:39,0
Test 2: 170 cm, 85 kg, 263 watts 03:59,0 30:07,0 26:08,0
Test 2: 170 cm, 85 kg, 263 watts 03:59,0 30:07,0 26:08,0
Test 2: 170 cm, 85 kg, 263 watts 30:07,0 56:15,0 26:08,0
Test 3: 175 cm, 85 kg, 266 watts 03:51,0 30:03,0 26:12,0
Test 3: 175 cm, 85 kg, 266 watts 03:45,0 29:57,0 26:12,0
Test 3: 175 cm, 85 kg, 266 watts 29:57,0 56:09,0 26:12,0

Here we’re. Ride on! Paolo



Clearly Zwift is not using the Cycling Power Lab formula. We should probably also consider rolling resistance, but going from 70 to 85 kg, rolling resistance should only increase by about 2%, so that won’t account for the difference.

If I have some time I’ll try to fit your data to some equations and calculate the power increase (according to Zwift’s physics) that would be required for a 175 cm 85 kg rider to keep up with a 170 cm 70 kg rider.

Does Zwift ever announce the winners of their challenges where irl prizes are involved? If so, where?

I’m still waiting for my notification that I won some Assos bib shorts…

Thank you!

To be continued on Ant+ simulators & speed tests


Full stem weight with rider in full TT gear: 81kg
Bike: Shiv TT, Front Zipp 900 w/ Vittoria Corsa cx tubular tire with a slow leak, rear Zipp 900 w/ Bontrager XXX tubular tire.
Rider: ~181- almost 182 cm, POC tt helmet, BioRacer SpeedConcept suit, Specialized Sub-6 shoes

CdA: a slow .223 with the custom 13cm risers. I would be almost offended if my avatar had a CdA of .24 or .27 :joy: