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    ReferenceSpeed Tests

    How Rider Weight Affects Speed on Zwift

    Eric Schlange
    By Eric Schlange
    January 16, 2020
    104

    Any cyclist worth their chamois knows that body weight is a huge performance factor for riders. The more mass you have to move, the more power you have to put out to move it!

    And this is true no matter what road you may ride. Sure, weight matters the most on climbs. But it’s also a factor on flats and descents.

    We decided to do some testing to see just how much each kilogram of weight slows (or speeds) a rider on Zwift. Our tests included flat roads, climbs, and descents. And they answer that eternal question: should you work to lose weight, or invest your money (Drops) in a faster virtual ride?

    We found the results quite interesting, and we think you will, too.


    A few notes about our tests:

    • All tests used a 183cm (6′) tall rider riding at 300 watts on the Zwift Aero frame with Zwift 32mm carbon wheels.
    • We ran each test at two different rider weights: 75kg and 82kg. We went with a 7kg difference because Zwift HQ says this is the weight difference between Zwift’s lightest and heaviest bikes. So the speed differences you see below could be realized purely through equipment changes in game!
    • Riding at higher or lower wattage or being significantly heavier or lighter than our test riders would impact time gaps somewhat, but we choose to keep the tests simple so the results would be easy to understand.

    Effect of Rider Weight on Climbs

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

    Test Results

    • 82kg @ 300 watts: 54 minutes, 49 seconds (13.4kph)
    • 75kg @ 300 watts: 49 minutes, 31 seconds (14.8kph) – 318 seconds faster

    Climb Test Observations

    Not surprisingly, up the steep Alpe climb is where we can really see how much weight affects rider speed. The time gap here is over 6x what we see on the flats! This is why lightweight riders win mountain races outdoors while the heavier sprinters struggle to finish within the time cutoff.

    Conclusion: reducing your body weight by 1kg will save you ~45 seconds up Alpe du Zwift.

    Effect of Rider Weight on Flat Roads

    Flat tests were completed over two laps of the Tempus Fugit route.

    Test Results

    • 82kg @ 300 watts: 52 minutes, 17 seconds (39.7kph)
    • 75kg @ 300 watts: 51 minutes, 26 seconds (40.4kph) – 51 seconds faster

    Flat Test Observations

    While some Zwifters like to say “it’s all about pure watts on flat roads,” it’s not that simple. Weight does affect your speed on the flats in Zwift, since it changes your computed CdA. Or to put it another way: two riders of the same height but different weights will have different CdA values in Zwift, meaning the heavier rider will need to push more watts to keep up with the lighter rider, who is encountering less (virtual) air resistance.

    Conclusion: reducing your body weight by 1kg will save you ~9 seconds over an hour-long flat race effort on Zwift.

    Effect of Rider Weight on Descents

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

    Test Results

    • 75kg @ 300 watts: 10 minutes, 7 seconds (72.5kph)
    • 82kg @ 300 watts : 10 minutes flat (73.3kph) – 7 seconds faster

    Descent Test Observations

    Riders complain about getting dropped on descents in Zwift, but that isn’t because the algorithm is computing speed incorrectly. The real reason riders get dropped on Zwift descents is that the pack keeps pedaling on the downhills. If you aren’t putting out power on a downhill in a race, you’ll get dropped–no matter what you weigh. Unless you supertuck smartly.

    Conclusion: reducing your body weight by 1kg will cost you 1 second on a 10-minute Alpe du Zwift descent.

    Buying Upgrades, Riding Up Grades

    The great Eddy Merckx famously said, “Don’t buy upgrades, ride up grades.” He was making the point that, if you want to be a better rider, training is the way forward. Buying more expensive equipment will get you marginal gains, but increasing your power and/or reducing your weight will get you greater gains, without impacting your bank account!

    Our test results above coupled with hundreds of additional test laps show an notable “2kg line” in Zwift performance on flat roads:

    • The difference between the fastest frame + wheel combo and a basic racing setup (Zwift Aero frame with Zipp 808 wheels) is 18 seconds over an hour ride. This is roughly the same time improvement you would see by dropping 2kg of body weight.

    If you’re carrying a few extra pounds and find yourself concerned about your Zwift race bike setup being a bit slow–see if you can shed some weight. Dropping just 2kg (4.4 pounds) will have the same effect as upgrading your basic Zwift ride to a top of the line racer, assuming you’re able to maintain the same power.

    There is also a “1kg line” for Zwift performance on steep climbs like the Alpe:

    • The difference between the fastest frame/wheel setup on climbs and a basic racing setup (Zwift Aero frame with Zipp 808 wheels) is 52 seconds over an hour climb. This is roughly the same time improvement you would see from dropping 1kg of body weight.

    If you still haven’t unlocked the Lightweight Meilenstein wheels atop the Alpe, there’s a way to make up for it: losing just 1kg will save you more time than those wheels ever could. Time to start counting calories, perhaps?

    An Important Note

    If you’re overweight, losing those unhealthy pounds can improve your cycling performance both on Zwift and outdoors. But any attempts at weight loss should be handled carefully, and ideally under the watchful care of a qualified professional.

    In a competitive, weight-based, results-driven environment like bike racing it’s easy to go too far and actually damage your body with extreme dieting or disordered eating.

    Read “RED-S: One Athlete’s Story” for more on this topic.

    Your Thoughts

    Inspired to shed a few pounds? Surprised by the results above? Share any questions or comments below!

    Note: This is a simplified version of the original post. The first version was revised after it generated a lot of confusion that distracted from the goal of learning “how much faster you’ll be if you lose 1kg of weight.”

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      Eric Schlange
      Eric Schlangehttp://www.zwiftinsider.com
      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

      104 COMMENTS

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      104 Comments
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      Dave Lee
      Dave Lee
      3 years ago

      As always, really good work Eric! Thanks.

      8
      Reply
      Craig Evans
      Craig Evans
      3 years ago

      At 183cm/118kg (6’/260lb) I am the definition of a Clydesdale. Since getting on the bike again and Zwifting, my weight is coming down. As the weight comes off and I ride more and harder, my watts are increasing, and importantly for how distance and speed is calculated in Zwift my w/kg is increasing. Merckx was partially correct – but he uses the wrong conjunction. It isnt an either/or proposition, you want both. Greg LeMond says it best – “It never gets easier, you just go faster.”

      16
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Craig Evans

      If you can drop weight AND increase power, you’re doing it right, Craig. Keep up the good work, and enjoy watching that w/kg number bump up!

      6
      Reply
      Steven Heller
      Steven Heller
      3 years ago
      Reply to  Craig Evans

      It always pleases me to hear of other Clyde cyclists out there; we have unique struggles in the cycling world. I assume from this statement you are not weight doping, and neither am I. I am 185cm/124.7kg (6’1″/275lb) and have not weight doped. Yeah, the “easy” D group rides are a workout for me, but I can hold on. My weight is also slowing dropping and my watts are increasing. Best of luck out there on your journey!

      13
      Reply
      Michael Martin
      Michael Martin
      3 years ago

      That being said how many people put their true weight into the metrics???

      3
      Reply
      James Daley
      James Daley
      3 years ago
      Reply to  Michael Martin

      Er, me! I can only hope to achieve moral victories anyway.

      38
      Reply
      Shawn Schmitz
      Super Member
      Shawn Schmitz(@beachgrad05)
      3 years ago
      Reply to  Michael Martin

      I do because I want my data to be able to show my true improvement as I lose weight and get fitter.

      35
      Reply
      Luc Caubergh
      Luc Caubergh
      3 years ago
      Reply to  Michael Martin

      Een minder gewicht inzetten is jezelf bedotten 😀

      2
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Michael Martin

      I think the vast majority of folks play fair. I know I do! But sure, there are some weight dopers.

      5
      Reply
      Stephane Staelens
      Stephane Staelens
      3 years ago
      Reply to  Eric Schlange

      in races I have the feeling that a lot of the riders are cheating, I know for myself that I can ride the speeds outside as I achieve in zwift. Hope zwift will take measures in the future for more faire racing and riding in zwift.

      2
      Reply
      Alan Jolly
      Alan Jolly
      3 years ago
      Reply to  Michael Martin

      I link my Garmin. Account to Zwift and weight is transferred automatically. I gained four kg last year and my ADZ time slowed by 6 mins (48- to 54) despite putting a lot of work in. I wish I didn’t like beer and carbs so much!

      14
      Reply
      Martin Jensen
      Martin Jensen(@martinhjensen)
      3 years ago
      Reply to  Michael Martin

      Most honest people do, the only one you cheat in games or like such by cheating is yourself. 🙂 – So is it worth it to use inputs that is not right and get no real satifaction or gain out of it ?

      2
      Reply
      Tara
      Tara
      3 years ago
      Reply to  Michael Martin

      I do lol or what’s the point?

      1
      Reply
      Martin
      Martin(@m_hotte2000)
      3 years ago
      Reply to  Michael Martin

      ??? Do you? I prefer to think that big majority is honest. Looks like you don’t have faith in humanity!

      0
      Reply
      Herringbone
      Herringbone
      2 years ago
      Reply to  Michael Martin

      I’ve just discovered my zwift weight syncs automatically with my fitbit scales, so this is quite good motivation.

      3
      Reply
      Alex Watson
      Alex Watson
      2 years ago
      Reply to  Michael Martin

      Yes I do

      0
      Reply
      Dave Daly
      Dave Daly
      2 years ago
      Reply to  Michael Martin

      Yeah I’m strict with the weight I put in. 180cm and Currently float between 81kg and 83kg over a week. So I put in 82kg. Even if I weigh in at 81 before a ride, I don’t change it until I weigh an average of 81kg over 3 weigh ins through the week…. Zwift is like golf in my opinion. If you cheat, you’re only cheating yourself.

      2
      Reply
      Stewart Howell
      Stewart Howell
      2 years ago
      Reply to  Dave Daly

      Good point you make about the averaging Dave.

      between the start and the end of a hard workout, it’s normal to lose nearly a kilogram in weight. This is not only in sweat but also in what we exhale.

      Not to mention the obvious that eating a main meal or going to the toilet, also affects what we see on the scales.

      0
      Reply
      Rad
      Rad
      1 year ago
      Reply to  Michael Martin

      I know it’s an old subject but I just found it together with your comment. I am, at this moment in time based on Zwiftpower lists of my events, probably the heaviest zwifter out there. I am gradually losing weight but I made a resolution to update my record in 5kg decreases. I am close to update it with 5kg less any day now. Whats the point of cheating myself? I am happy if I can finish an event a few places from the bottom. That’s my reward.

      2
      Reply
      mchritton
      mchritton
      11 months ago
      Reply to  Michael Martin

      Thanks to a DC Rainmaker article, I have an inexpensive scale that links to my phone via Bluetooth which then updates my weight to Zwift. Still a clyde but an accurate clyde.

      1
      Reply
      Bobby Mac
      Super Member
      Bobby Mac(@rmacdowell1)
      3 years ago

      Great analysis!! And spot on follow-up comparisons utilizing the data to show that the indisputable best upgrade is almost always a loss of a few pounds! As a (current) 82kg rider, who can hang with the very front A/B group on an entire flat race, but gets dropped like a sack of cement out of a four-story window the second we hit any proper climb, this is a sad but true reality. :chuckle:

      7
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Bobby Mac

      I’m right there with ya, @Bobby Mac.

      2
      Reply
      PET3R
      PET3R
      3 years ago
      Reply to  Bobby Mac

      Im 81 kg but I have the opposite. I can do 3,0w/kg avg for an hour flat, but on a climb I can do 3.5 to 3,8. Standing I do 4,0 w/kg. So my best results are always on rides/races with climbs

      2
      Reply
      Dave Daly
      Dave Daly
      2 years ago
      Reply to  Bobby Mac

      Feel your pain!!!

      0
      Reply
      Stefan Judex
      Stefan Judex
      3 years ago

      I read this article with great interest a couple of weeks ago when you included a comparison to the (simulated) real world. Why did you take the comparison out … which I thought was the most interesting piece? Too many death threats from lighter riders? 🙂

      1
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Stefan Judex

      A couple reasons, actually. One is that the real world calculators all return different numbers–some that are more in line with Zwift’s speeds and some that are not. So there’s confusion there, and I didn’t want to paint the picture that Zwift gave an unfair advantage to any particular set of riders.

      But the bigger reason was that I thought it distracted from my goal of the post, which was simply to show how much faster you’d be on Zwift if you lost 1kg.

      2
      Reply
      Stefan Judex
      Stefan Judex
      3 years ago
      Reply to  Eric Schlange

      Thanks. Really appreciate your thoughts. Still … I think your original idea was very intriguing

      1
      Reply
      Duncan Edwards
      Duncan Edwards(@duncan_xs)
      3 years ago
      Reply to  Eric Schlange

      Glad I saw this comment, I’ve just spend around 60 minutes trying to find the article where you compare Zwift rider weight speeds with the real world!
      I’m not a big believer in the Mandela Effect but was seriously starting to doubt my own sanity when I could only find this article, which looked exactly the same, yet for some reason missed the key lines I was looking for.
      Unfortunately I’m still a 90kg rider on Zwift, though on the plus side, appears I haven’t quite gone completely insane just yet!

      2
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Duncan Edwards

      … yet. Ha!

      0
      Reply
      Stewart Howell
      Stewart Howell
      2 years ago
      Reply to  Duncan Edwards

      I feel for you Duncan, I’m the same… I can’t give up when I know there is something somewhere in the cloud that I have seen or even wrote myself before, and now I can’t find it. I’ve spent far more time looking for it than it would take to simply write it again.

      0
      Reply
      Bob Smith
      Bob Smith
      3 years ago

      Would be a lot more interesting/pertinent if the test was based on w/kg since Zwift categories are based on w/kg. Comparing 300w @ 82kg = 3.65w/kg and 300w @ 75kg= 4w/kg would expect the higher w/kg to be faster. However, what is the time difference on flat/climb/downhill between a 82kg @ 3.25w vs 75kg @ 3.25w?

      16
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Bob Smith

      I’m working on a post along those lines, actually. We’ll see how long it takes for me to finish!

      9
      Reply
      Sondre Dahlskaas
      Sondre Dahlskaas
      3 years ago
      Reply to  Eric Schlange

      Great! This is what I was looking for while reading the article.

      0
      Reply
      Palle Raahauge
      Palle Raahauge
      2 years ago
      Reply to  Eric Schlange

      Any update on this? I drive at 2.5w/kg, but weighing in at 100kg I really struggle uphill compared to lighter riders doing the same w/kg.

      0
      Reply
      Chris
      Chris
      2 years ago
      Reply to  Palle Raahauge

      You should go faster than lighter riders doing the same w/kg (see Zwift Insider article called speed tests at equal w/kg or something like that). Obviously depending on your FTP and their FTP if it is a long climb the other riders might be able to hold power for longer, but you should go the same speed or faster for equal w/kg on climbs as well as flats

      1
      Reply
      Emilio
      Emilio
      6 months ago
      Reply to  Eric Schlange

      Hi there. I was wondering if finally you post that article. Becuase, since riding in Zwift, I wonder if the w/kg eliminated the weight contribution, or the light one had an advantage, probably becuase it would have less aero resistance.

      0
      Reply
      Rex Weaver
      Rex Weaver
      3 years ago

      The phrase in the excellent article that needs re-read by all who want to gain speed by losing body weight is: “assuming you’re able to maintain the same power”. Can those who are not returning from layoff or injury lose 4.5kg or so and maintain the same power? I would like to hear from those who have accomplished that.

      1
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Rex Weaver

      That’s always the hard part, isn’t it?

      0
      Reply
      Shawn Schmitz
      Super Member
      Shawn Schmitz(@beachgrad05)
      3 years ago

      Currently working on my weight. I personally won’t weight dope as I want MY results on Strava/Garmin Connect to be capable of showing MY personal improvement. I don’t race but group rides are tough to keep up even the slow ones due to my weight. It gets suggested to weight dope so can stay with group. I want my results and PR’s to be mine and not because I digitally lost weight. I just recently lost 1kg+ as I am working on my diet and weight. Thanks for the awesome info as always.

      8
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Shawn Schmitz

      Keep up the good work, @Shawn Schmitz!

      0
      Reply
      Chris Holton
      Chris Holton(@bass_n_bass)
      3 years ago

      good test but if you tested more than 2 weights it might be interesting to see if the relationship is linear or curved, is it really as simple as saving X seconds per kg or is it a law of diminishing returns or does it actually increase the effect the more you lose?

      5
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Chris Holton

      It’s a pretty linear thing, actually. I just kept the data simple, but all the way from 50kg-100kg it’s a pretty linear thing.

      4
      Reply
      M4rk0
      M4rk0
      3 years ago

      So what you’re saying is that I’m fat.

      7
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  M4rk0

      You said it, not me! 😯

      2
      Reply
      Chris Schafer
      Chris Schafer
      3 years ago

      Good stuff Eric! I enjoy reading your posts. 🤙🏻

      2
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Chris Schafer

      Thanks!

      0
      Reply
      Flex Rampant
      Flex Rampant
      3 years ago

      Thanks for this Eric, interesting indeed. I realise it’s not something that can (easily) be altered IRL but I’d love to know the difference an individual’s height made to speed/time.

      1
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Flex Rampant

      Here you go, @guest_30447: https://zwiftinsider.com/how-height-affects-speed-in-zwift/

      2
      Reply
      Brent
      Brent
      3 years ago

      I am not a physicist but I did stay at a Holiday Inn Express – it might be interesting to look at descending as well.

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      3 years ago
      Reply to  Brent

      I did. See “effect of rider weight on descents” above. 😉

      1
      Reply
      Robert Barrett
      Robert Barrett
      3 years ago

      If people weren’t “inspired” to weight dope already, this will inspire them 🙂

      Having been at 68kg +/- 1kg for around 40 years I have just managed to hit 67kg with a target of 66kg for a real world hilly 25TT.

      Good to know that I will have some gains in the virtual world from my weight loss efforts !!

      I’d say cheers but one of the requirements is no alcohol – empty calories 🙂

      0
      Reply
      Mike
      Mike
      3 years ago

      Hello everyone at Zwift
      I really enjoy your website and am an avid participant .
      I would like to request if you could set up races or training for 65 years and over Riders .
      Sometime it is difficult to pair up with the younger generation !
      Thank you
      Mike V.

      4
      Reply
      Martin
      Martin(@m_hotte2000)
      3 years ago

      Very interesting. But you don’t mention that heavier riders usually produce more watts. Naturally heavier on the pedals and bigger muscular mass. As a lighter one, I always prefer hill where it’s a matter of w/kg. On flat I struggle, having to produce much higher w/kg than most other rider…

      0
      Reply
      Duncan Edwards
      Member
      Duncan Edwards(@duncan_xs)
      3 years ago
      Reply to  Martin

      Question is of course, do bigger riders produce more power simply because they’re bigger or are riders bigger because they produce more power?
      Personally, as someone who’s spent a fair amount of my youth in the gym doing strength work and eating correctly, I find it interesting in Zwift that smaller riders seem to think extra power is just something that’s natural with weight rather than earned.
      There’s always an option to work hard to add weight as well as to lose it.

      2
      Reply
      Tim Schneider
      Tim Schneider(@tasmobile)
      3 years ago

      I had lost about 5 kg over the past several months but was reluctant to change my avatars weight thinking I was faster in flats so you can bet I’m changing my in game weight to reflect my true weight based on this info.

      0
      Reply
      Andy
      Andy
      2 years ago

      Hi Eric I have noticed that my avatar is a bit porky love handles etc. If i was to lose some weight will my cycling screen buddy look a bit neater as well.

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Andy

      There are three avatar body types, based on BMI thresholds. See https://zwiftinsider.com/avatar-sizing/ for details.

      0
      Reply
      Andy Medhurst
      Andy Medhurst(@andy_medhurst)
      2 years ago

      Eric, I have been re-reading this article with added interest. This is in order to understand why I have been struggling to compete against heavier riders during my recent flat TT events. I have experienced heavier riders maintaining a higher speed on the flat due to being able to produce more watts and still not exceeding the overall category limit (Cat C – 3.2w/kg). I wonder if you did the tests using the category limit (3.2w/kg) as the static value and not for a set power value this would show more of a difference. So for a 75kg rider @… Read more »

      1
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Andy Medhurst

      Yes: if you’re a lighter weight rider, you’ll perform better vs the competition when there are climbs involved, assuming you and they are both near the category w/kg limit.

      1
      Reply
      Andy Medhurst
      Andy Medhurst(@andy_medhurst)
      2 years ago
      Reply to  Eric Schlange

      Thanks, it’s so easy to get your understand confused when trying to come to terms with all the variables as well. Really appreciate the articles and information you publish, clear and concise. Looks like it’s off to Bologna for me.
      Cheers, Andy.

      0
      Reply
      Remy
      Remy(@xxxx_gambit_xxxx)
      2 years ago
      Reply to  Eric Schlange

      Eric … can you supplement this article to include a comparison test at a static wkg instead of absolute 300w output. On a unscientific test I did, the heavier rider outperform the lighter rider on flats and climbs when riding at the same wkg.

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Remy

      Already done, Remy! See https://zwiftinsider.com/wkg-tests/

      2
      Reply
      Floris
      Floris
      2 years ago

      Dear Eric, thank you. I just started in Zwift and I have a (stupid) question. Should I enter my ‘naked weight’ or include the weight of my bycicle?

      2
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Floris

      Naked weight. Your bike weight will be added to that (and it varies depending on which bike/wheelset you use!)

      0
      Reply
      edmond dixon
      edmond dixon
      2 years ago

      I love zwift, but weight pens on the alpe is unfair as it is not true climbing…IRL climbing is much much harder as you really are carrying your weight, O n zwift you are not doing this..it does not matter if you are 60kgs or 100kgs! So if I took 5kgs off my profile weight, my time up the Alpe would be nearly 4 mins quicker?

      0
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      Tim
      Tim
      2 years ago

      Eric, really appreciate all the info you provide. However, having read all about how uphill speed is calculated I still can’t understand how a rider putting out 2.1 w/kg on the ‘bonus climb’ was riding away from me convincingly as I put of 3.1… no kit seems to have that much impact.
      Do you have any insights?
      Thanks!

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      Reply
      John J Keepers
      John J Keepers
      2 years ago

      Each route has a characteristic joule/kg. Is this available anywhere?

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      Reply
      Dan Connelly
      Dan Connelly(@djconnel)
      2 years ago

      I am surprised the speed improvement on L’Alpe was apparently 10.7%, while the change in (inverse) weight was only 9.3% And that just includes rider mass. If I add in an assumed 6.8 kg for the bike, 2 kg for clothes and such, the weight advantage is down to 8.4%. And that doesn’t include wind resistance, which would further reduce the speed advantage. I can’t think of any physics in the standard power-speed model which would cause speed to increase “faster” than weight changes. Here’s how I’ve personally treated height, BMI, and wind resistance: If I assume CdA is proportional… Read more »

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      Reply
      Matteo
      Matteo
      2 years ago

      How can I tackle the descents as quickly as possible?
      Thanks and good week.

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      Reply
      phil
      phil
      2 years ago

      Just to confirm, the w/kg that zwift displays and uses, is based on the weight of the rider plus the weight of the bike he is riding, correct?

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      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  phil

      No. w/kg never includes the weight of the bike, even when you talk about it outdoors. Just rider weight.

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      Reply
      Ben
      Ben
      2 years ago

      Something that’s always confused me…when entering weight, should it include being fully kitted up in shoes, or in your birthday suit…ahem..? Does Zwift account for the weight of shoes for example when calculating CdA? Just wondering what the standard weighing process is?

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Ben

      All the Zwift clothing has weight included. So I weight myself in my birthday suit, or just a kit…

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      Reply
      Jeff Cunningham
      Jeff Cunningham(@trijdc)
      2 years ago

      Normally my weight is automatically uploaded to Zwift every morning from my Withings scale. The other day I weighed on a regular scale and went to manually input my weight and noticed that you can only use whole numbers. Does that mean that Zwift is always rounding my weight to the nearest whole Kg even though Withings provides a more precise number? ZwiftPower seems to use the more precise number. No big deal, but it just got me thinking :).

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      Rich Lovelock
      Rich Lovelock
      2 years ago

      Hey Eric, this is a great article. I’m unclear if you can derive from these tests what two riders of different weights, pushing the same w/kg will end up doing and who would be fastest?

      Your test of the lighter rider pushing the same, 300 watts, as the heavier rider, resulted in the lighter rider being quicker, with higher w/kg. Would be interesting to see the same test matching w/kg (as opposed to pure watts), maybe you’ve done this already?

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      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Rich Lovelock

      Yes, see https://zwiftinsider.com/wkg-tests/

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      Andy Peterson
      Andy Peterson
      2 years ago

      Hi Eric — any idea if weight (rider + bike + wheel) affects acceleration in zwift? I feel like I accelerate through packs more quickly with hard efforts on a light bike than a more aero bike. But it might just be in my head.

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      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Andy Peterson

      I would think it does, although it’s hard to test because we just don’t have the granularity in the data that we need. Now, whether you’ll feel much of a difference between two different bikes… I think that’s probably more in your head than anything else. But that doesn’t make it a bad thing. 🙂

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      Robert L Kraft
      Robert L Kraft
      2 years ago

      I think there is a problem with the fact that weight isn’t factored around BMI or body fat percentage. Coming from bodybuilding I weigh 200 but can leg press over 1000 and can attain around 16 to 17 miles per hour sustained for 20 miles real world. Last week did a 1 mile climb at 8 percent grade and never went below 4mph. First night on zwift and my leg are moving furiously in big gear front and middle gear back on what seemed like a small hill. Zwift said 2mph….

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      Brandon
      Brandon
      2 years ago

      Hi Eric, just wanted to know if zwift takes bike weight into the equation

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      Ron
      Ron
      2 years ago
      • 82kg @ 300 watts: 54 minutes, 49 seconds (13.4kph)
      • 75kg @ 300 watts: 49 minutes, 31 seconds (14.8kph) – 318 seconds faster

      I estimated from another empirical model that the time savings are between 200-250seconds on an average 8.5% slope so there’s nearly a minute extra in your analysis. Are you setting this up on an emulator? Good article anyway…

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      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Ron

      Using an ANT+ simulator to send our bot up the Alpe, yes. Did you do your tests without any drafting? We do ours solo, so the rider doesn’t interact with any others that would influence his speed…

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      Michael
      Michael
      2 years ago

      Hi Eric, i am ex track cyclist who has put on a (quite) few pounds. I have found your analysis really good and interesting. My wife has had enough of me whinging about me not being able to stay with any of the Zwift D races! I have lost kg since getting back on the bike and feeling much stronger. It is getting really frustrating not being able to keep up. Last race I started at 350w everyone rode away from me. At 350w I still do not record a 3 kg/w ratio. Wife says just change weight to 70kg,… Read more »

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      Eduee Santiago
      Eduee Santiago
      2 years ago

      Eric,

      I am new in Zwift and my apologies for my question in advance. So based on this post, yes, it is true that Zwift take your weight in consideration when climbing to simulate your real climb

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      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Eduee Santiago

      Absolutely true!

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      Reply
      EskrimaDiva
      EskrimaDiva
      2 years ago

      Hi Eric My partner and I zwift ‘together’. He’s 6’1″ weighing 213lb and I’m 5’4″ weighing 129lb. When he cycles on zwift with his true stats loaded he trails me, but when he fibs and puts his stats the same as mine, he disappears into the distance ahead of me. He thinks that by putting our stats the same, he puts us on an even playing field…. is this true? or does his actual body mass on a static trainer give him an advantage over me because of his weight down through the pedals? Just to add… out on the… Read more »

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      Robert
      Robert
      2 years ago

      So to be exact, do I need to type my weight in the morning after peeing into zwift or is it the weight that I have on the bike (how would you know that??)

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      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Robert

      It’s just your own body weight. Bike weight, etc is added to that by Zwift’s physics engine.

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      Reply
      mike
      mike
      2 years ago

      Fantastic article. All my mates buying carbon race bikes for 8000 pounds should look into getting rid of their monstrous beer guts first! But buying a bike lots easier than losing weight. Lol!

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      FvK
      FvK
      2 years ago

      Hello everybody! My experience with this is somehow different. I’m a quite heavy but strong rider (108kg and ~390 watts ftp). Today I raced the ocean lava cliff side route (Cat. A) and was easily able to hold on to the 2nd group in the steep climb (first part of epic KOM reverse). When I take a look at the race results I always have the lowest avg w/kg of all the riders around me… Any thoughts on this?

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      Reply
      James Hassan
      James Hassan
      2 years ago

      Hi Eric, I’m new to Zwift and have been concentrating on hilly routes, at 89 kilos I really suffer going uphill as expected but I think I maybe doing it all wrong. I rode Epic Kim today with my cadence 60 to 70 rpm, would my overall time differ if I spin the gear a bit more?

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      Matt
      Matt
      2 years ago

      What about for us LIGHT riders that are getting smoked on the flats does it make sense for us to go heavier on frames?

      0
      Reply
      Eric Schlange
      Author
      Top Member
      Eric Schlange(@eschlange)
      2 years ago
      Reply to  Matt

      If you’re getting smoked on the flats, it makes sense to go with the most aero frame possible. And become really good at drafting…

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      Reply
      James
      James
      1 year ago

      I’m 6’6″ and 90kg. This means I’m getting heavily penalised for both height and weight.

      I don’t think the Zwift calculation works well for people like me, as I find I’m being dropped easily by riders in Zwift that I can out-climb and out-race in the real world.

      Any advice, except losing weight 😂

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      Reply
      Neil L
      Neil L
      1 year ago
      Reply to  James

      Thanks for creating this article Eric. So now I know why I beat all my mates up hills in Zwift and conversely get dropped downhill without peddling hard

      I’m genuinely 65 kg and 5’9″ with an FTP of 2.4 w/kg. Out on the road my buddies all pass me going uphill (no stamina, me) but I go downhill quicker (presumably cos I’m more aerodynamic. Completely opposite to my mates. So it’s nice to beat them even if it isn’t real.

      1
      Reply
      Paul Smith
      Paul Smith(@smithpauld1501)
      1 year ago

      Taking an idea from your drafting tests, do you have any thought of running tests at 200 or 225w?

      As a long-term D rider, I suspect without data that the benefits of super-aero bikes are proportionally less at lower speeds AND weight penalties are proportionally greater.

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      Reply
      Ebrahim
      Ebrahim
      1 year ago

      Not sure if this was discussed in the comments. But a more interesting perspective is how much of a difference riders of different weight, gain or lose time while riding the same w/kg up a climb or on the flat. Or how much more savings does a lighter rider gain while slipstreaming as compared to a heavier rider.

      0
      Reply
      Syafiq
      Syafiq
      1 year ago

      Thank you for this good information. Btw, do you have this published on a journal, conference or books? Thanks in advance!

      0
      Reply
      Graham Hughes
      Graham Hughes
      1 year ago

      Great article Eric, when I started to use Zwift I was around 77kg and after a few months riding it dropped steadily to around 75kg and held there, however I stopped drinking some 8 months ago (just decided to stop, no real reason, just one day said no thanks) and the weight dropped off to a now very steady 69kg with no dieting or extra exercise. it really didn’t bother me not having a beer/wine and was no hardship at all, I am amazed that the alcohol made such a weight difference. I may return to having a cold beer… Read more »

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      Reply
      Michael
      Michael
      1 year ago

      Hi Eric. Great work. I would like to see a bit different test: watt required to uphold 40 km/h (perhaps also 35 and 45) as a function of rider weight on the flat (perhaps also grade 5 and 10). That is, the x-axis would be rider weight and the y-axis would be watt (perhaps an additional interesting plot would be a different y-axis with rider watt/kg). Hope you find it interesting enough to do. Thanks

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      Reply
      John
      John(@profjohnbowers)
      1 year ago

      Where did the 1kg conclusion numbers come from and what justifies them? Is the power, gradient, weight -> speed function linear? If it’s not, which I don’t think it is, you can’t just say well a 7kg difference is 318 seconds so a 1kg difference is 318/7=45s difference. That works only if the function is linear in mass. But acceleration is linear in mass, which means velocity is squared since it integrates acceleration. This means that the difference in speed in the first kg increase in weight will be less than the difference between the 6th and 7th kgs in… Read more »

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      Reply
      Alexander
      Alexander(@a_vikulin)
      1 year ago

      In an AutoCat race I saw a 35kg rider with a 4.5w/kg FTP, who was placed in Cat D. Was wondering whether he is really equivalent to a 70kg rider with a 2.5w/kg FTP.
      Lower in the comments found your article https://zwiftinsider.com/wkg-tests/ which explains a lot. Thanks!

      Last edited 1 year ago by Alexander Vikulin
      0
      Reply
      Neil Townsend
      Trusted Member
      Neil Townsend(@ntownsend)
      5 months ago

      Hi Eric, I wondered if you had thought about redoing the two “heavy” tests (and maybe even the height ones as well) given the changes in rider dynamics over the last couple of yeas?

      0
      Reply
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