Speed Tests: Steady w/kg Across Various Body Weights

Speed Tests: Steady w/kg Across Various Body Weights

In an earlier post, we dug into how rider weight affects speed on Zwift, specifically calculating how much each kilogram of weight slows (or speeds) a rider on Zwift.

Many readers asked us for similar data based on watts per kilo. That is, if we hold w/kg steady, how much does each kilogram of body weight (and the corresponding additional wattage required to maintain the same w/kg) slow or speed the rider on Zwift?

First we summarize the data, then we discuss conclusions. Enjoy!


First, a Disclaimer

Zwift is a rich simulation of outdoor riding in which many variables are taken into account to provide a realistic experience. What we’re trying to do here is show simplified test results to illustrate basic cycling physics which apply in Zwift and outside.

There are many, many variables which these tests do not include: varying rider heights, drafting, bike weight or aerodynamics, rider posture, etc. Our goal here is to focus on w/kg. But in practice, there is a lot more going on!

All of our tests were done using a single rider in isolation – so no draft effect. This rider was 183cm (6′) tall and used the Zwift Aero bike with 32mm Zwift wheels.


The Data

Climb Test

Climbing tests were completed up Alpe du Zwift, an 8.5% average gradient which is 12.2km long.

Power to weight ratio (w/kg) is a very good predictor of speed on steeper climbs. For example, we see here that two riders of wildly varying weights (50k to 100kg) are separated by only .6kph when they both hold 2w/kg.

  • When holding 2w/kg: every kilogram of weight + 2 watts makes you ~0.012kph faster
  • When holding 3w/kg, every kilogram of weight + 3 watts makes you ~0.016kph faster
  • When holding 4w/kg, every kilogram of weight + 4 watts makes you ~0.022kph faster
  • At 75kg, each additional w/kg increases your speed by ~3.55kph

Why is there a speed difference at all, and why is that difference greater at 4w/kg than 2w/kg? Read “Conclusions” below for further discussion.

Flat Test

Flat tests were completed over two laps of Zwift’s Tempus Fugit route, a 0% average gradient which is 34.6km long.

Speed varies significantly on flat roads between riders of different weights who are holding the same w/kg. For example, the speed difference between 50kg and 100kg riders both holding 2w/kg is 3.8kph. And like the climb test showed, this speed difference is even greater at higher w/kg: the difference between 50kg and 100kg riders at 4w/kg is 5.5kph.

Notice also how the speed gap between 2w/kg and 3w/kg is wider than the gap between 3w/kg and 4w/kg? Again–it’s just physics! As you speed up, each additional kilometer per hour requires more added power than the one before.

  • When holding 2w/kg: every kilogram of weight + 2 watts makes you ~0.076kph faster
  • When holding 3w/kg, every kilogram of weight + 3 watts makes you ~0.084kph faster
  • When holding 4w/kg, every kilogram of weight + 4 watts makes you ~0.11kph faster
  • At 75kg, each additional w/kg increases your speed by ~4.4kph

Descent Test

Descent tests were completed down Alpe du Zwift, an -8.5% average gradient which is 12.2km long.

Here we see the largest speed difference between rider weights, and this makes sense because gravity is now working in favor of the heavier rider.

  • When holding 2w/kg: every kilogram of weight + 2 watts makes you 0.206kph faster
  • When holding 3w/kg, every kilogram of weight + 3 watts makes you 0.21kph faster
  • When holding 4w/kg, every kilogram of weight + 4 watts makes you 0.214kph faster
  • At 75kg, each additional w/kg increases your speed by ~1.95kph

Conclusions

Our Zwift test results don’t tell us anything an experienced cyclist hasn’t already learned outdoors. Still, let’s discuss some of the findings and how they’re applicable to riding and racing on Zwift.

Don’t Attack on Descents

Look at the speed difference between each w/kg band on the climbs or flats versus the descent. Notice how the speed difference is much greater on climbs and flats. This (along with safety concerns outdoors) is why you don’t see riders putting in big digs to attack on descents: the speed you gain just isn’t worth it!

Example: on the Alpe descent, if a 75kg rider bumped up their wattage from 2w/kg to 4w/kg, their speed would increase by 3.9kph, or 5.7%. If they had put in the same effort on flat ground their speed would increase by 8.8kph, or 28.2%. More than double the difference! But get this: put in that same effort while climbing the Alpe and the rider’s speed increases by 7.7kph, or 92.2%. This is why racers attack on climbs–because you can put massive time gaps into the competition.

Heavy Wins

As the road gets steeper, riders at the same w/kg will see their speeds coming together. On a steeper climb like the Alpe, speeds stay quite close together, varying at the most in our tests by just 1.1kph (between 50kg and 100kg riders both at 4w/kg).

But why is it that when two riders are holding the same w/kg, the heavier rider will always be faster? There are multiple reasons, actually–but one big reason is what we’ll call “true w/kg”–that is, including the weight of the bike in our w/kg number.

Suppose we have two riders, 100kg and 50kg, both riding at 3w/kg. But let’s say they’re on 9kg bikes. If you add that bike weight to the rider’s weight and calculate the true w/kg, you get this:

  • 100kg rider + 9kg bike @ 300 watts = 2.75w/kg
  • 50kg rider + 9kg bike @150 watts = 2.54w/kg

So even though both riders are holding 3w/kg, the heavier rider is holding a higher true w/kg.

Another reason heavier riders go faster is that, unless you’re climbing straight up (which is impossible), your effort isn’t only lifting you up the hill–it’s also driving you forward by overcoming the forces of air and rolling resistance. Heavier riders are putting out more pure watts than lighter riders, meaning (in simple terms) there are more watts available to overcome air and rolling resistance after the lifting is done.

But Light Really Wins

But let’s not misinterpret the data. While the heavier rider always wins at the same w/kg, what we see in reality is that it’s really tough for a heavy rider to hold high w/kg. Making 400 watts of power is much more work for a 100kg rider than making 200 watts is for a 50kg rider.

So while our theoretical 100kg rider would be faster up the Alpe at 4w/kg than the 50kg rider at 4w/kg, there are very few 100kg riders who can hold 400 watts all the way up the Alpe! By comparison, there are many lightweight riders who can hold 4w/kg all the way to the top.

At the upper echelons of our sport, there are riders who can hold 6w/kg+ for over an hour. But those riders never weigh 100kg! The biggest are perhaps 80kg (Cancellara), but most are closer to 60-70kg (Froome, Dumoulin).

But Heavy Wins (Until the Climbing Starts)

On the other hand, if we look at Zwift’s standard w/kg-based race categories in light of the data above, it’s not hard to conclude that lighter riders face a significant disadvantage in flat races. Yes, you won’t find many heavy riders able to hold 5w/kg to win A races, but you will find plenty of heavier riders who can hold 3.1w/kg, meaning they could race as a C and really put the hurt on lighter riders. (In a flat race, a 100kg rider at 3w/kg will travel over 3kph faster than a 60kg rider holding 3w/kg.)

This is why many flat C races are won by racers weighing 90-100kg. Check out the category C results of this recent race, for example.

So what’s a lightweight D, C, or B racer to do? Skip the flat races. Enter events with significant climbs, where speed differences between weights are much smaller! If you’re able to hang with the heavier riders on the flats, then punch it up the climbs at a higher w/kg than the heavy riders can sustain, you can create the winning selection.

Longer-term, we’d like to see results-based categorization take the place of w/kg-based categories. But until that happens, lighter riders will need to race smart on the flats, attack on the climbs, and perhaps lobby for more climbing races.

Larger Variance at Higher Power

As watts per kilo increase, the speed difference between riders of varying weights also increases. So we see up the Alpe the 100kg rider is .6kph faster than the 50kg rider at 2w/kg, yet at 4w/kg the 100kg rider is 1.1kph faster. Almost twice the speed difference. Why is this?

Again, our “true w/kg” idea explains most of this difference:

  • At 2w/kg, the difference in true w/kg between a 100kg and 50kg rider is 0.14w/kg
    • 100kg rider + 9kg bike @ 200 watts = 1.83w/kg
    • 50kg rider + 9kg bike @ 100 watts = 1.69w/kg
  • At 4w/kg, the difference in true w/kg between a 100kg and 50kg rider is 0.28w/kg
    • 100kg rider + 9kg bike @ 400 watts = 3.67w/kg
    • 50kg rider + 9kg bike @ 200 watts = 3.39w/kg

Your Thoughts

Got questions or comments? Share them below!

About The Author

Eric Schlange

Eric runs Zwift Insider in his spare time when he isn't on the bike or managing various business interests. He lives in Northern California with his beautiful wife, two kids and dog. Follow on Strava

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Donald ( GH70) Silas

I weigh at times between 190 and 210 lbs. Climbing is an albatross. Not only am I heavy, an unseen factor is my 32″ weightlifter thighs consisting of energy gulping, fast fatiguing, fast-twitch muscle fibers. My climbing has to be deliberate, controlled and steady. It’s not the speed factor that controls pace, it control of fatigue that controls speed. Just did the Apple at 2.0 work, 1.5 rest, steady pacing. Thanks for your info.

Sheridan Halls
Sheridan Halls
1 year ago

I normally love your stuff, but I think there would have been better choices of route than Alpe de Zwift as it contains so many flat sections that it will skew the data. You really need to rerun this but on a much more consistent climb without all the regular flat sections. I don’t know which hill would be best, as my Zwift knowledge is nowhere nears yours!

Scott Fryer
Scott Fryer (@fryup2000)
1 year ago
Reply to  Sheridan Halls

I dont think any hill on zwift will have a consistent grade all the way. I guess the alpe taking so long does help to iron out any anomalies.

Sheridan Halls
Sheridan Halls
1 year ago
Reply to  Eric Schlange

Fair enough, I stand corrected and apologise. I’ve always felt like it had quite a few flattish sections. Maybe they were so well needed when they arrived that they were very noticable!!!

Henry Heavisides
Henry Heavisides (@henryheavisides)
1 year ago
Reply to  Sheridan Halls

Think I must have missed all of the flat sections on Alpe du Zwift…….did I take a wrong turn?

Aoi Niigaki
Aoi Niigaki
1 year ago
Reply to  Sheridan Halls

I think you might be confusing the climbs. The two big ones on Zwift are the Epic KOM and the Alpe du Zwift (which is a copy of Alpe du Huez). The Epic KOM has many flat sections while the AdZ does not and is a consistent climb.

Alex
Alex
1 year ago
Reply to  Sheridan Halls

I am posting while climbing Alpe du Zwift and can assure you the flat stretches are extremely short and far between..

Eric O
Eric O
1 year ago
Reply to  Sheridan Halls

There are some “flatish” sections on the Alpe; however, they are short and primarily going around the switchbacks. Other than that, some occasional grade drops to 4-5% can FEEL flat when you are otherwise climbing at 9-10%!

Ryan
Ryan
10 months ago
Reply to  Sheridan Halls

Hi Sheridon,
The test was over 12.2kms at an average gradient of 8.5%. Whether that is made up of 18% pinches and some descents isn’t really relevant (although, in reality The Alpe is a consistent climb with not too much variation). Perhaps after a 10% segment you are finding the 6-7% gradients feel relatively flat? Reminds me of climbing the Stelvio, when the gradient flattened to around 4-5% I was like, wow this is awesome, some respite but then I’d look at my Garmin and realise I was actually still climbing.
Oh to be climbing the Stelvio again..

Dan Connelly
Dan Connelly
10 months ago
Reply to  Ryan

Suppose you can ride 40 kph on the flats. Wind resistance is proportional to speed cubed. So if you’re climbing at the same watts, but going half the speed, that’s around 7/8 of the power going to climbing, 1/8 to wind (there’s also rolling resistance, but neglect that for a moment). Now the climb gets steeper, and you can go only 1/3 has fast. So now 26/27 of the power goes to climbing, 1/27 to wind resistance. In each case wind resistance is small, and climbing is most of the power. So until your speed gets to well over half… Read more »

Scott Fryer
Scott Fryer (@fryup2000)
1 year ago

Good article, thanks! I guess this also shows that if you get dropped on the summit of a climb then digging deep to get back to the bunch on the descent is even harder!

Gari
Gari
6 days ago
Reply to  Eric Schlange

all depends on your descending skills as most descents aren’t straight. Or on zwift which wouldn’t matter 😂

Bruce Bastian
Bruce Bastian
1 year ago

Nice article. I would really like to see results-based categorisation or at least something better than what they have now. I did the 2020 Tour of Watopia as my first foray into racing. It was a lot of fun and I now plan to do more. I’m a newbie so I’m kicking it with the guys in Cat D. Every stage I’ve entered so far has been won by guys doing 4-4.5w/kg. In one stage, the D winning time was 3 minutes slower than the A winning time. I’m still overweight and underpowered, so it doesn’t really bother me now,… Read more »

Ryan
Ryan
10 months ago
Reply to  Bruce Bastian

Hi Bruce, did you check the Zwift Power results? I used to get upset with people pushing unrealistically high watts in races. But now I try find a realistically strong bunch to ride with and then check the results in Zwift Power after the race. The fliers in the race usually don’t have any results in Zwift Power, so I take that as my real placing, rather than the placing in the Zwift Companion app.

David Hull
Super Member
David Hull (@dhull7k)
1 year ago

Thanks, this is very helpful for folks like me who are new to this and trying to work out how best to apply their limited w/kg! With respect to your campaign for better race categorization I’d like to understand how that would affect those of us near the bottom. Being near the bottom end of the C group (in your Forever Losing category) I rarely do well enough in a race to pick up points. But I usually find some riders around my w/kg level and have a good race. If you categorize based on race results does that mean… Read more »

Mr Richard Neil
Mr Richard Neil (@richardneil)
1 year ago

For me, as a 70kg rider who can typically push out 3.3 to 3.4W/Kg for an hour or so this is just depressing, although it confirms what I have been thinking for a while. Most Zwift races tend to be shorter (sub 1 hour), on flat courses, and a rider like myself at the lower end of cat B stands no chance, especially with the tenancy for starts to be maximal efforts by heavier, more powerful riders. Recently I have been riding Cat C races, knowing full well I’ll be DQ’d by Zwift Power, but at least having the ‘enjoyment’… Read more »

Henry Heavisides
Henry Heavisides (@henryheavisides)
1 year ago

I am in a similar situation to you. I have just been upgraded from C to B on zwift power, as my 20 minutes w/kg is 3.25. I weigh 71kg. I was mediocre in C races…..which are usually won by much heavier riders with a lower w/kg. Now I’m way off the pace in B races.

David Hull
Super Member
David Hull (@dhull7k)
1 year ago

I’m in your situation but at the lower end of C. Its going to take me a long time to get anywhere near the top of the group. In the meantime my strategy is to let the top riders charge off out of the gate and try to link up with a group that’s slightly above my w/kg. If I can hang onto their wheels until the race settles down I find I can be competitive and make my own “race within the race”.

MarkE
MarkE
6 months ago
Reply to  David Hull

I know this is super late, but 6 months ago I was in your boat and now I fairly regularly podium in C. What made the difference for me was that initial effort. I found that instead of letting the fliers fly away, if I kept up with them for the first 1-3 minutes, the pace settled down quite a bit, at least until the last 300 meters or so.

Geoff
Geoff
1 year ago

Richard,

My weight and FTP are almost exactly the same as you so i feel your frustrations.

I don’t even bother racing in zwift because of this issue. I am really hoping that Veloton becomes a real thing.and provides a more realistic option for those in our situation. It certainly looks fantastic if they can finally release it.

Colin
Colin
1 year ago

Looking at these results a slightly different way…..

On the flat, a 50 kg rider holding 3 w/kg is putting out 150 watts and traveling at 33.8 kph. While a 100 kg rider, also holding 3 w/kg, is putting out 300 watts and traveling at 38 kph.

So the 100 kg rider is putting out twice the power (100%) but moving only 12% faster.

That doesn’t seem realistic.

Blair
Blair
1 year ago
Reply to  Colin

Speed isn’t linear to power. The faster you’re moving, the harder it is to go even faster.

Colin
Colin
1 year ago
Reply to  Blair

True.

In this test the rider is the same size and weight, so we can just look at the change due to increasing velocity from 33.8 to 38 kph. Power to overcome aerodynamic drag goes as velocity cubed. I make that to be a 42% increase, or 63 watts.

Let’s also add in the increase in rolling resistance due to increasing mass from 50 to 100 kg. I make that to be 23 watts.

150 + 63 + 23 = 236 watts.

Where are the other 64 watts going?

Dan Connelly
Dan Connelly
10 months ago
Reply to  Colin

A reasonable Crr for Zwift is 0.4%. Calculate this for each rider and I get: 50 kg: 18.4 watts 100 kg: 41.4 watts subtract that off and I get: 50 kg rider: 131.6 watts (against wind) 100 kg rider: 258.6 watts (against wind) Then I can calculate effective CdA, assuming air density = 1.2 kg/m³: 50 kg: 0.265 m² 100 kg: 0.366 m² The ratio is 1.38. This suggests the cross sectional area is relatively close to the square root of the mass, assuming equal height. If you think of the body as an ellipsoidal cross-section of constant eccentricity, then… Read more »

Aoi Niigaki
Aoi Niigaki
1 year ago
Reply to  Colin

In the real world doubling your watts would make you about 30% faster. If it takes you 180 watts to travel at 30kmh then you’d need about 360 watts to travel at 40kmh. However, in Zwift I suspect the rider weight (along with rider height) is also used to calculate the drag coefficient. A lighter rider has less aero drag so not only are these tests changing the watts they are also changing the aero drag which helps the lighter rider partially overcome their lower watts.

Colin
Colin
1 year ago
Reply to  Aoi Niigaki

So: 33.8 kph * 1.3 = 43.9 kph

That sort of feels right to me….

Simon Hodgson
Simon Hodgson
1 year ago
Reply to  Colin

According to gribble

100kg at 300w is 38kmkh
50kg at 150w is 31kmh

23% Faster

Kevin Bouchard-Hall
Kevin Bouchard-Hall
1 year ago

I think this is a great, and difference in speed at various weights is not unique to Zwift. The same phenomenon happens outside. My question is how closely does this scale to what happens outside? Is Zwift more or less generous to pure watts vs wt/kg?

Susun
Susun
1 year ago

No doubt, Zwift is about w/kg…even in the flat
In real world it’s more about pura absolute watts in the flat

Dan Connelly
Dan Connelly
10 months ago
Reply to  Susun

That’s not really true. See for example:
Heil DP (2002) Body mass scaling of frontal area in competitive cyclists not using aero-handlebars. Eur J Appl Physiol 87(6):520–528

Rick B
Rick B
1 year ago

I got highlighted in one of your articles!!! I personally prefer big boned. I always knew there was an advantage for being heavier just not how much.
Another way of seeing this is by looking at the zwift rankings for C. All but one of the top 10 are over 85kg.

Yolo
Yolo
1 year ago

You should provide a power vs speed graph. Wkg doesn’t normalize the data as cda becomes a variable independent of gravity.

George Stacko
George Stacko (@gcastacko)
1 year ago

Great article Eric! I have a question that is a little off topic. I race as a B and weigh 83.9 kg . I typically can hold 3.5 most races but I’m curious when Kiss has a 100k race on Sundays I can’t hold 3.5 for that long typically for that long of a race I would be right around 3.1 to 3.2 . Do I still race as a B and get smoked but if I race as a C for the long race do I get Dq by ZwiftPower?

Rick B
Rick B
1 year ago
Reply to  George Stacko

You would race your zwift power category. Which sounds like is B. All other riders should be in a similar boat and see a fall off from their 20min or 60min power.

Mats
Mats (@matsaadde)
1 year ago

So I’m a heavier rider, actually 100 kg exactly. On the flat and on the climb I’m doing 2.3-2.7wkg, not much difference. The lighter riders keep up with me on the flats By just putting Out 0.2-0.3 wkg more but on the climbs they push out 4-4.5 wkg. Why don’t they go at 4 wkg on the flat too since they obviously have that Capacity? Is it because they are lazy, whinging bastards..?🤓👍

Stéphane Louvet
Stéphane Louvet
1 year ago
Reply to  Mats

They just attack where they have the best chances to succeed. It’s non sense for them to attack an heavy rouleur on the flat.
Try to drop them on the flat, slide at the rear of the pack, build up your speed as you move to the front and use the slingshot effect to escape.

sven
sven
1 year ago
Reply to  Mats

What is your power profile?
https://www.trainingpeaks.com/blog/power-profiling/
If you are interested in results, try to pick race courses (including TT), that best suit your profile.

Ric
Ric
1 year ago
Reply to  Mats

Ha. They’re just being smart racers. 🙂

sven
sven
1 year ago

Thanks Eric. Nice analysis (as always!). I am curious to know what a similar analysis would look like for Zwift dirt/gravel on a road bike. I assume that is also a good place to attack, and gives an added advantage to riders able to put out more absolute watts rather than w/kg similar to IRL?

drnoodle
drnoodle (@kdstotes)
1 year ago

Innsbruckring is really the case study. As a larger rider I can hold onto a pack all day on the flat but once w hit the city climb I’ll out the back. However if I can sag-climb and stay close enough to the little ones, I can put in a dig maybe 20m before the right hand turn at the top. This gives me the separation to keep them out of my draft on the descent and then I’m gone. I can usually completely recover by the next little bump. Then I can ride that down and if I can… Read more »

Mick Such
Mick Such
1 year ago

You seem to have forgotten about the Age of riders.
As you get older, you do get slower.
I can’t compete against a rider weighing the same but is some 20 years younger.
I’m blowi g out of my bottom trying to keep up, let alone passing him/her. 😋

Ric
Ric
1 year ago

Great article, Eric. I really appreciate the science and writing you do.

Simon Davies
Simon Davies (@simon_davies)
1 year ago

Do you know if this graphs along the same lines or is there a blip every 25kg? The reason I’m asking is that at nearer 130kg than 100kg these numbers generally don’t work for me, I’d like to understand if I can just take these numbers and grow the graph out to show what I “should” be expecting and measure that against what I see on ZwiftPower to measure my performance.

Just trying to get the courage to ride Alpe but by my reckoning I’m looking at nearer 2 hours than 1.

Simon Davies
Simon Davies (@simon_davies)
1 year ago
Reply to  Eric Schlange

Thanks Eric.

B. Key [DIRT]
B. Key [DIRT]
1 year ago

Things will continue to favor heavier riders unrealistically until autobreaking in sharp corners are implemented. You see less heavyweight wins across categories for outside races because 1) repeated accelerations, say in a crit, will wear out/drop 100 kg riders faster due to simple physics, and also 2) 100 kg riders rarely can sustain an aero position as in Zwift…

Ryan Hughes
Ryan Hughes
1 year ago
Reply to  B. Key [DIRT]

I’d have to disagree. As a 85+kg racer, a lot of being efficient comes down to simple racecraft which Zwift will not be able to implement. Sticking in the top 5-10 of a crit pack has no braking at any corners. Hanging in the middle or back is a huge waste of effort with the yo-yo accordion effect. Also “100 kg riders rarely can sustain an aero position” is the same as saying 65kg riders can’t sprint.

Ryan Hughes
Ryan Hughes
1 year ago
Reply to  Ryan Hughes

Autobraking is a bad idea.

I can tell you that as a former Cat 2 road racer in Colorado who has achieved all of my best results through criterium racing, auto-braking doesn’t happen in real life unless you need to work on your racecraft. Zwift is a game and it will be impossible for them to implement the skills needed outdoors to transfer to indoor results.Ride at the front of the pack and every corner is smooth.

Don
Don
10 months ago
Reply to  Ryan Hughes

Maybe “autobraking” is the wrong word. I’ve also got plenty of criterium racing experience, and although you should absolutely be minimizing any braking during a real life crit, you DO slow decelerate coming into corners and accelerate out of them. It is not a constant speed. As a lighter rider, the more corners in a crit (as well as gradient changes), the better, as I felt that the repeated accelerations (small though they might be) generally did not fatigue me as much as it did the heavier riders.

Ryan Hughes
Ryan Hughes
1 year ago

Great article. This is something I’ve always wondered about. 🙂

Ben Haggett
Ben Haggett
1 year ago

The downhill weight advantage makes me think that’s the ‘real’ reason for the zwift supertuck, it just levels the field that little bit. I use it every chance I get and it really helps keep me from blowing up when trying to hang with powerful heavier riders on downhills.

Ant L-S
Ant L-S
9 months ago
Reply to  Ben Haggett

It helps me recover after nearly burning myself out trying to stick with lighter climbers on the ascent.

Alex
Alex
1 year ago

Great post!

I am one of those lightweight triathletes (61kg, 288 FTP, 4.7w/kg) who has zero chance to compete on flat courses. If I want to be able to stick with the front group on a flat race, I have to sign up for category B.

Geoff
Geoff
1 year ago
Reply to  Eric Schlange

Eric,
How happy would you be with zwift if you had to cheat (sign up for the wrong category) in order to be remotely competitive on flat and rolling races in zwift (most races on zwift)?

Rich Lovelock
Rich Lovelock
1 year ago

Great analysis, would be interesting to see *how well* this represents real world physics, I guess you could put numbers in to bike calculator

Geoff
Geoff
1 year ago

The following paragraph taken from the above blog doesn’t seem to make sense to me as it applies to zwift. You say the following Eric.. “So while our theoretical 100kg rider would be faster up the Alpe at 4w/kg than the 50kg rider at 4w/kg, there are very few 100kg riders who can hold 400 watts all the way up the Alpe! By comparison, there are many lightweight riders who can hold 4w/kg all the way to the top” Because of the way zwift categorizes riders in races, that doesn’t matter. If there are no heavy riders who can hold 4 w/kg… Read more »

Pablo Escowatts
Pablo Escowatts
1 year ago

W/KG = watts per kilogram. more kilograms = more watts. more watts = more speed. It’s always been right there in the category description, takes some people years to understand it, if they ever do, some still think dropping weight is an advantage.

j.richey
j.richey
1 year ago

Thanks Eric.
As leader of a ride with a 2.0 – 2.5 W/Kg ride I really appreciate this data. It’s interesting and I will try to pass it along.
(I plug this site every ride because it is a wealth of all knowledge Zwiftful)

Vlada
Vlada (@demon2307)
1 year ago

Well done Eric. So the chart shows two riders of the same age, with the same lifestyle. However, there are very few such couples. Performance at different ages cannot be measured.

J. Rabbit
J. Rabbit
1 year ago

I have a question not directly related to this, but about racing and maybe w/kg. Whenever I enter a corner with a pack, it seem I usually (frequently? – way over half the time) am the one who is moved to the outside of the turn, has to take the longest path, and loses a couple of meters.Do you know how it is determined, who gets the inside of the corner? It doesn’t seem to be order in the pack – maybe w/kg as you enter the turn?

Vlada
Vlada (@demon2307)
1 year ago
Reply to  J. Rabbit

Zkus Zwift fórum. Někde jsem o tom už četl

Simon Hodgson
Simon Hodgson
1 year ago

According to gribble
100kg rider at 200w does 32kmh on the flat.
50kg rider at 100w does 26kmh on the flat

So both 2wkg including 7kg bike weight.

why are the numbers so much bigger than your Zwift numbers?

Susun Corda
Susun Corda
1 year ago
Reply to  Simon Hodgson

Because Zwift’s physics are not realistic and doesn’t fit with the facts on the road… it’s all.

Susun Corda
Susun Corda
1 year ago

I think that Zwift is clearly NOT realistic on the flat. I think it’s not considering the effect of inertia generated by weight,as in the real world, when you are moving over 40km/h is easier to mantain speed for the heavier riders, so they accumulate more kinetic energy that help to overcome wind resistance (as the main opposite) with rolling resistance too. Gravity is not the main thing on the flats, so… w/kg is only important maybe in accelerations. Real world experience in ITTs reveals that lighter riders (weights around 60kg) moving even 6W/kg on the flat… have no chances VS heavier… Read more »

Team U.F.O.
Team U.F.O.
1 year ago

This is EXACTLY why I hate climbing! Give me the desert any day! (Yes, I know…lose the kgs….but I love food, beer and wine too much!)

Eibert Van't Hof
Eibert Van't Hof (@e_vanthof)
1 year ago

Interesting again and best explanation so far on being beaten nu heavier riders. Just too bad there”s a lack of true hilly races. Having a top 20min wattage in your cat hardly ever matters.

On side note, after reading this; would this also mean the 50kg rider has less advantage of a TT bike on Zwift, compared to the 100kg rider? Since the weight penalty of the added weight has a higher penalty for the 50kg rider, given the “true wkg”?

Jon M
Jon M
1 year ago

I’m a ‘bigger’ guy in cycling circles- 90kg at just over 5’10″/1.79m. This is my experience… out of the seat I can generate much, much more torque than the small guys. Put me on a steep section and I can grunt up it, lighter guys have to spin up. So long, shallow climbs? I suck. Steep, short sections? I love ’em. As to whether it’s unfair that a heavier guy with equivalent power-to-weight travels faster. HELL NO! I’m heavy because I carry more muscle. Because I choose to participate in other sports the penalty is I need a bigger cardio… Read more »

Andy M-I
Andy M-I
1 year ago

Completely agree with these conclusions. I’m a 67KG, 180cm rider with an FTP around 4W/KG. Even so I’m always struggling to hang on to the lead group in flat B races. However for routes that finish on a climb, assuming I can get to the climb near the front, things are very different and I can ride most people off my wheel.
It would be great to see a few races split along both weight and power to make things fairer, maybe not all the time, but occasionally.

Webvan
Webvan
1 year ago

“But let’s not misinterpret the data. While the heavier rider always wins at the same w/kg, what we see in reality is that it’s really tough for a heavy rider to hold high w/kg. Making 400 watts of power is much more work for a 100kg rider than making 200 watts is for a 50kg rider.”

Not arguing with the fact that 100kg riders don’t win mountain stages, but why would it be harder for a 100kg rider to maintain 4w/kg than for a 50kg rider ?

Rich S
Rich S
11 months ago

Loved reading this bit of data – since the data is to hand it would be very interesting to plot similar graphs showing plots of pure watts or speed… so say I’m 80kg, I could use the data to see what wattage I would need to put out to keep up with someone who’s 65kg pushing 250W 😀

Hamish E K Greagor
Hamish E K Greagor
10 months ago

What about crit type races that involve lots of accelerations? Does the lighter rider benefit enough from having to accelerate less mass every time to overcome the pure watt difference?

Dan Connelly
Dan Connelly
10 months ago

I didn’t read all of the comments, but my feedback would be it isn’t the absolute speed difference which matters (km/hr), but the fractional difference which matters. So for example, what is the fractional change in time from the fractional change in weight. On a “pure climb” with zero bike/clothing weight, a 1% increase in mass makes you take 1% slower. If you now add bike weight, a 1% increase in mass makes you (to first order) 1% / (1 + f) slower, where f is the starting fraction of weight from the bike + stuff. When wind resistance is… Read more »

David Copp
David Copp
9 months ago

https://www.zwiftpower.com/events.php?zid=920829 Hey Eric … I wanted you to have a quick look at this Tempus Fugit Time Trial I was just in … I finished at 26:00, with a 346 watt average … I had a fairly steady pace, and probably ranged between 320 watts and 380 watts for the whole race. I was riding the Specialized Shiv Disk TT bike. If you look the at 5th place finisher, with a time of 25:45, he only averaged 224 watts. Now, I know there’s a large weight difference (111 kg for me, vs 55 kg for the 5th place finisher), and… Read more »

Wouter
Wouter
8 months ago
Reply to  David Copp

Yes… would like to hear your thoughts on this as well, Eric. This is a pretty absurd outcome, on a pancake flat course like TickTock.

Wouter
Wouter
8 months ago
Reply to  Wouter

*Tempus Fugit

B. Key [DIRT]
B. Key [DIRT]
5 months ago
Reply to  Wouter

Perhaps a much smaller rider as well ? Should compare heights too…

pbernstein 76
pbernstein 76
4 months ago

When will Zwift consider some age group activities? I am 65kg with a current 191 http://ftp…at age 75+ it would be not much fun if I were to be interested in more than just getting a good workout. No way I have the same capacity as some 30/40/50/60 yo…tia

Kenny Wilson
Kenny Wilson
1 month ago
Reply to  pbernstein 76

I only started Zwifting early this month but am just a boy of nearly 60. Like pbernstein above, I’d love to see age categories too. Currently, I’d be quite happy to race but once I’ve rid myself of my Christmas belly I’ll be sitting on the wrong side of Cat C. I’d be floundering less than half way into a Cat B free for all. I’m perfectly content to enter real world CX races for that sort of humiliation. . However, I’m not unhappy. In Zwift, I’ve discovered something which has enhanced my riding experience beyond anything I could have… Read more »

Nicklas Karlsson
Nicklas Karlsson
3 months ago

It would be interesting how the aerodynamics is calculated. Is a 100kg person just a “scaled up 50kg person” when it comes to front-facing surface area. Personally, I’m drop-shaped 😉

nick smith
nick smith
2 months ago

Watts per kg works well on steep climbs as a predictor of speed, whereas just watts works for modest downhills. Over an average course of up, down, and flat, presumably the best predictor of overall speed would be watts divided by weight to the power of n, where n is between 0 and 1 – any idea what n should be?

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