Still waiting on an ultra light rider update

Racing
116

It is based on a rider wearing an aero kit, in an aero position.
I compare my road bike (7.8kg) equiped with aero cockpit, 45/55mm wheels, vittoria corsa 28mm tubeless tires, and me with aero cycling kit, aero road helmet, used to riding hands in the curb of my bars, elbows at 90 degrees… an aero position.
My average speed is identical irl and in Zwift when I ride in the « fastpack » (on tuesdays we have these fastpack rides, everyone riding in a big pack with powerful relays in front).

I think that if you have ideal conditions like I have, you will get your best results and they will be identical to Zwift.

1 Like
117

Basically what you are telling us is that your are not able to sustain for a long time an aero position on your road bike (we don’t even know if your road bike is aero…), so you doubt the results of others.
I can tell you it is possible to ride for a long time in an aero position. I do and a lot of riders do. I am not even talking of Ironman riders in itt position for 180km…

People should stop thinking only about their experience.

I understand that it is not because I am able to keep this position for a long time that you can. But Zwift is a game, in which it is normal to do as if you were trained.
If you want bad aero, just use the safety bike.

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118

Very very good idea! (The breakaway power up)… or you could have it at the beginning and decide to use it when you want (it could be like an aero helmet, working longer, but only if you don’t have any draft AND don’t give any draft to anybody)

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119

FYI:

I see that ZwiftInsider has done some speed tests:

Possibility #2: Zwift’s Calculations Include Assumptions Which Do Not Reflect Your Outdoor Rides

We compared those numbers to two different online bike calculators, setting them to 25 degrees Celsius, 50m elevation, 8kg bike weight, riding in the drops, and default values otherwise. Here are the results:

  • 300 watts, 100kg rider
    Zwift Carbon, 32mm carbon wheels: 38kph
    Specialized Venge S-Works, Zipp 858 wheels: 38.9kph
    BikeCalculator.com: 39.16kph
    Kreuzotter.de result: 37.1kph
  • 225 watts, 75kg rider
    Zwift Carbon, 32mm carbon wheels: 35.8kph
    Specialized Venge S-Works, Zipp 858 wheels: 37.2kph
    BikeCalculator.com: 35.77kph
    Kreuzotter.de result: 34.8kph
  • 150 watts, 75kg rider
    Zwift Carbon, 32mm carbon wheels: 30.8kph
    Specialized Venge S-Works, Zipp 858 wheels: 31.4kph
    BikeCalculator.com: 30.55kph
    Kreuzotter.de result: 30kph
  • 150 watts, 50kg rider
    Zwift Carbon, 32mm carbon wheels: 33.7kph
    Specialized Venge S-Works, Zipp 858 wheels: 34.4kph
    BikeCalculator.com: 31.44kph
    Kreuzotter.de result: 31.7kph

As you can see, Zwift speeds are generally within 2kph of the bike calculators, with the greatest difference being at the 150 watts/50kg rider test where the difference between one calculator and our fast test setup was 2.96kph.

Note that this is on a course with a 50m elevation.

120

I want a “sit behind my team car until the commisars see me” powerup when i’m dropped.

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121

Interesting article. What’s a bit odd is the article premise is to explain premise that Zwift speeds are 1-4 km/h faster, and then go on to show against the Zwift Carbon bike:
Scenario #1: Right in the middle of the 2 calculators
Scenario #2: .03 kph higher than 1 calculator, 1kmh higher than the other
Scenario #3: less than 1 kmh higher than either calculator

For the lightweight rider, where there is an obvious 2-3 kmh difference, there’s no explanation for the somewhat outlier result difference. I’d hazard a guess that if you tried an even lighter weight rider, the kmh difference would increase further. Would like to see a 200 watt, 40kg rider example.

EDIT: worth pointing out also that all examples used a 175cm height rider because it’s a national average – whether that makes sense for a 50kg vs 100kg rider is another story.

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And that is the only thing we can read from that test. A trend towards greater difference for the lighter rider.

There could of course be that both the calculators are wrong/worse than Zwift’s calculations, but it is hard to know for sure. It looks like the BikeCalculator.com is closest to the Zwift Carbon results.

A few more data points, with also varying heights, would be nice.

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and drop the height from 175 cm to something like 165 cm…Ducati beating is my guess.

128

I think this tells you all anyone needs to know.

129

These test is not hard to do, with all the people just on this thread it should be able to knock this out in a week.

Just set the weight and height pick a bike and do a ride in ERG. Create a meetup with no other riders visible.

don’t wait for someone else to do it.

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131

Congratulations. You are the most aero small human on Earth :joy:

I asked the broad question with a very clear objective.

To demonstrate that the Zwift model is based on absolutely ideal circumstances. You must understand that you are categorically an outlier? Very aero and very small. There are a vast range of riders in real life. You are basically saying Zwift picked the math perfectly for you.

I’m saying, they should have picked something better representing the middle of the bell curve. Absolutely, not me, nor you. An average cyclist. Which is unsurprisingly, a vast majority of the user base…

Because aero load increases exponentially, there ‘could’ be a small benefit to changing the overall in game CdA load to being higher? I am unsure of the math, but hypothetically, could it not help to reduce the overall power required to break away from a group?

I’m struggling to get my head around it.

One of the issues I suspect that is causing the very light riders exaggerated game speed is rolling resistance. I suspect that Zwift has the tarmac set at near perfect conditions. For a majority of riders globally, tarmac is light years from perfect.

Smaller riders suffer a huge penalty on poor chip seal or rough tarmac, as it is a significant portion of their lower overall power.

I believe that if Zwift increased the overall tarmac rolling resistance affecting all riders, it would go a long way to stopping sub 45kg riders having an unrealistic performance advantage.

We need a math/physics expert to run some simulations…

As a light rider myself, I’m actually campaigning here to essentially slow myself down more relative to larger riders.

Because, it would more accurately represent real life riders. Particularly the uber light children.

Again. this is just speculation. I’d love someone to do the math, either from Zwift or Zwift could provide their math and have the community help dig into improving it.

1 Like
132

Interesting.

Thanks for posting.

2.9kph is massive.

For a rider to average 2.9kph more speed constantly is essentially years of training. Multiple category increases etc.

I’d bet money that when you drop weight under 50kgs with further height reductions these flat speeds will be even more broken.

This information seems to back up my direct experience.

Zwift’s math / physics seems to be not working for light riders. The lighter rider, the greater the error.

I also suspect, it could be a little off at the heavy end too.

133

Concerning your rolling resistance recommendation, do the light wt youngsters seem to lose their advantage on the Jungle loop?
Not raced with one there so I don’t know.
Also, the jungle is half climbing so any rolling resistance changes maybe masked.

I think there should be a built-in governor that applies a limit the less you weigh.

Maybe alter rolling resistance based upon how much below 45 kg?

134

That would be a simple fix code wise I imagine.

It would be quite hard getting it real life relevant though, because where are we getting the data from?

How do we know how fast a certain rider will travel and how do we know if that has has any relevance to real life? In fact, does it even have to correlate?

My opinion is it should correlate to real life physics. I say this because that just makes more logical sense. At least it does to me.

If the physics are just some random game that has no bearing on reality, then fine. That works too.

However, in this hypothetical game world, 10 year old’s will continue to crush full grown adults.

Kids will love it :joy:

I haven’t raced Jungle Loop much, I do suspect you are right. From my own experience I do feel weaker relative to heavier riders on that surface. As I should as a light weight rider.

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Unfortunately rolling friction Frg is mass * (Cr) Rolling resistance coefficient. So if you increase the Cr you will increase it more for heavy riders than lighter riders.

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Zwiftinsider did a rolling resistance summary here. Rolling Resistance on Zwift: Crr and Watt Savings of Various Wheels | Zwift Insider

They found that the road bike/wheel on pavement took 36 Watts to maintain 40 kph for a 75kg rider on a 7Kg bike. You can also use that to get a pretty good idea of the air density, drag coefficient and rider surface area product that Zwift uses too given the other speed test data Zwiftinsider have published.

141

We do agree on almost everything…
the only difference between us is that I think that as a game, Zwift should feel fast, so it should simulate a rider wearing aero kit, on his bike in the most aero position.
You think this virtual rider should be mister everybody. Why not, but it is not very epic.
I think Zwift should give everybody a feeling of epic fast rides! That’s what a game is made for, feeling strong!

(you are right, I care about aero, a lot more than my friends, but I ride irl with 70-100kg fit friends with over 4 wkg ftp… so if I want to be able to stay with them on flat, I have to be very aero, as my ftp is good in wkg but I lack raw watts).

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Testing with BikeCalculator.com with the settings that ZwiftInsider seems to have used:

  • Rider weight: 50kg
  • Bicycle weight: 8kg
  • Temperature: 25C
  • Position: Drops
  • Tires: Clinchers

To travel at 33.7km/h will require 181W (Zwift Carbon)

That is significantly different from 150W.

I used the Zwift Carbon bike since it seems to be the one that matches the BikeCalculator results best for the other test cases.

EDIT: This calculator does not seem to use height as a parameter.
I tested with the Kreuzotter calculator which gives 179W for the same settings with height=175cm.

3 Likes
144

Is your 14 year old beating you on a road bike or MTB?
If MTB are you cross country or enduro?
I live in US Midwest, do cross country with some hills.
I have ridden MTB x 35 years and I have never seen a 14 y/o that could stay with me.
Most just don’t have the neuromuscular strength to really go anaerobic and recover.
I’m sure there are some in areas where MTB is more prominent.
Still, IRL kids that beat grown men are very very uncommon and it seems they are too common on Zwift.
I would say the same probably holds for Road rides too.

145

The 45kg a few years back is due to the weight limit. Zwift reduced that weight limit in 2020(I believe).