Why You’re Getting Beat by Riders with Lower w/kg

Why You’re Getting Beat by Riders with Lower w/kg

With the Northern Hemisphere winter in full force, we’re seeing lots of new Zwifters on course. Many have little or no experience riding with power–that is, measuring wattage output and understanding how watts affect speed in solo and group ride situations.

Fortunately, Zwift behaves very much like the real world in terms of physics, so any understanding you may have of outdoor cycling physics will translate to Zwift, and any additional understanding you may gain from Zwifting will transfer outside.

One common question people ask, especially in race situations, is “Why am I getting beat by people who are putting out lower watts per kilogram?” 

There are several answers to this question, but first make sure you understand how Zwift is calculating your speed. Secondly, understand that watts per kilogram (w/kg), or power to weight ratio, is your current wattage (the power you’re putting into the pedals) divided by your body weight in kilograms.

Example: I weigh 84kg, so if I’m putting out 300 watts my w/kg is 300/84=3.57

Now, back to the question. Here are the two top reasons why you’re getting beat by people who are putting out lower watts per kilogram.

#1: You Aren’t Staying in the Draft

Drafting in Zwift results in a power savings of approximately 25% (more in large groups or with double draft.) In other words, all other things being equal, a drafting rider only needs to put out 75% of the power a non-drafting rider is putting out to maintain the same speed.

If you’re “in the wind” on the front or off the back of a group, you will need to hold much more power than those who are drafting.

Tools like kreuzotter.de’s calculator can give you good numbers here which reflect outdoor and Zwift physics quite well.

Example from kreuzotter.de: a 75kg rider holding 225 watts will travel at 35kph. Another 75kg rider will be able to hold their wheel putting out 25% less power, or 169 watts.

Note: you cannot draft in Zwift on a TT frame. Others may draft behind you, but you will not receive any draft benefit.

Read an in-depth discussion of Zwift’s draft, including tips and tricks.

#2: You’re a Lighter Rider on Flat Terrain

Watts per kilogram is a good pace metric for climbs, where gravity is the main thing slowing you down. But pure wattage is a better metric for flat roads because once you get moving on the flat your speed is mostly determined by wind resistance and your wattage.

Because of this, when we take drafting out of the equation on a flat course, a heavier rider will always be faster than a light rider when both are doing the same w/kg–because the heavier rider is putting out more watts. This is true outdoors as well.

Example from kreuzotter.de: a 60kg rider and a 80kg rider both hold 4w/kg on flat ground. How fast are they traveling?

  • 60kg rider holding 240 watts travels at 37kph
  • 80kg rider holding 320 watts travels at 39.5kph

The 60kg rider would need to hold 288 watts (4.8w/kg) in order to keep up with the 80kg rider, if drafting isn’t taken into the equation.

The One-Two Punch

Where things really get tough is when #1 and #2 above both apply to you. If you’re a lighter rider who gets dropped from the pack on a flat course, you’ll have to hold a much higher w/kg than the group in order to catch that group again!

Here’s a simplified example with numbers pulled from kreuzotter.de’s calculator: let’s say you are a 60kg rider racing in a pack being pulled by a 90kg rider who is putting out 360w (4w/kg). The pack would be traveling at 40.6kph. Since you are drafting, you only need to put out 75% of the 312w it would take you to travel that same speed solo. That’s 234w, which is 3.9w/kg. Don’t miss this! Just to maintain your position in the draft your w/kg must basically match the heavier rider who is pulling in the wind.

Then if you get dropped and lose the draft’s 25% power savings, you’ll need to put out 312w just to keep pace with the group. That’s a whopping 5.2w/kg, while the guy pulling in the pack is still just doing 4w/kg. Couple this with the fact that others in the group can rotate through and take pulls so everyone stays fresh, and you’re going to have a very hard time catching the pack in this situation!

The Takeaway

Just like riding outdoors, lighter riders will be challenged to keep up with heavier, more powerful riders on flat courses. Stay in the draft to conserve energy so you can use it when it counts. And remember: you’ll get ’em in the hills!

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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..Alien King..
..Alien King..
1 year ago

Thank you for this Mr. Schlange and for clearing up those who think being a 60 Kilo rider is fun. You r for sure a great information data bank plus you get to use your math prowess. You sir are a true community asset and never stop doing what you do. Thank you for all you do and cheers to 2020 being a great year for you and no more power outages.
..Alien King..

Daniel Schmitz
Daniel Schmitz
1 year ago

Height is such a huge factor on Zwift, too since its a stand in for CDA. Zwift time trial results are heavily skewed to shorter rider on the flat courses. The worst thing to be on a flat course is tall and skinny.

stan crocker
stan crocker
1 year ago
Reply to  Daniel Schmitz

And yet, IRL we often excel at TTs

Dennis Keane
Active Member
Dennis Keane (@keane)
1 year ago
Reply to  Daniel Schmitz

I’m 6’5″ and about 195 – 200 lbs – so I meet your tall (and skinnyish) comment. I am regularly trounced by riders with lesser w/kg – due to height alone. Good thing I don’t have dreams of a future in pro cycling.

Wheezy Wheels
Wheezy Wheels (@richardneil)
1 year ago

Zwift time lag to respond (C. 10 sec?) is something to watch out for to avoid falling out of the draft. Staying in the draft requires more attention than IRL

Flanagan
Flanagan
1 year ago

Eric would also add that lighter riders should be very careful when cresting hills. As a larger rider (102kg w ~375 FTP) I try to stay at end of back of the front of the pack up the hill (top 10-20 positions) but really roll over the top hard. This can blow open small gaps because it gets the front group rolling through drafting off big watts and smaller riders can get gapped out and just unable to close what starts as a small gap to the drafting hard charging front group. When you get gapped at the top of… Read more »

Joe Bolan
Joe Bolan (@bolanbiker)
1 year ago
Reply to  Flanagan

No kidding. Got freight trained at the top of Box Hill this weekend. Silly me for pushing it up the hill. Gave ’em a gap to shoot, and bye-bye!

Shane Besler
Shane Besler (@shanebesler)
1 year ago
Reply to  Flanagan

that’s not very nice and how are you at the front on a climb at 230lbs. I thought it was the light riders that created the top of the hills first and opened up the gap further on the heavier riders???

Dan Connelly
Dan Connelly
5 months ago
Reply to  Shane Besler

Except in the top category, light riders do not have an advantage on hills, since riders get grouped together based on W/kg. This cancels the climbing advantage of light riders: they’re put in the same race with stronger, more powerful, heavier riders who are able to climb as well, but are advantaged everywhere else.

Peter Fullarton
Peter Fullarton (@midnight_poacher)
1 year ago

Yep, always find I go off too fast and can’t hold the wheel of the fast group so get dropped and realise I’m way ahead of the next group which is travelling the same speed as me. So there’s me on my own at 185cm tall and 64kg, not good but handy to know the info above now, I was wondering what was up! Thanks.

Walter Van den Broeck
Walter Van den Broeck
1 year ago

What about the impact of the bikes and wheels ? I’ve noticed quite some MTB’s in the Watopia jungle and Tron bikes on the climbs during recent races ?

Ian Tuck
Ian Tuck (@ituck)
1 year ago

I’ve often wondered about how hard it is to “catch the draft” of a group that’s approaching me from behind. Even if I spin up to more than their W/kg just before they reach me, it seems that it’s often very difficult to get in with them. Not sure how you’d model that, but wondering if you have any insight for the variables I’d need to take into effect. Does the draft take a few seconds to kick in, seconds in which they might actually have blown by me, even if I’m matching their wattage?

Gerrie Delport
Gerrie Delport (@gerriedelport)
1 year ago
Reply to  Ian Tuck

I would think it is more important to get to the same speed as the group behind you. You will need to put out a lot more power to accelerate to their speed. Once you are at their speed and they close the gap you should be able to hang in the draft. w/kg is a very bad metric to use on a flat road.

Sammy Knockaert
Sammy Knockaert
1 year ago

Q: is there a difference in drafting if behind larger guy or smaller guy, or is draft purely based on watts and wkg? Does height impact drafting for guys behind you? Can you get full drafting benefits in the bunch as a larger guy of 1m90 when others are all 1m60?

Dennis Keane
Active Member
Dennis Keane (@keane)
1 year ago
Reply to  Eric Schlange

This is good to know. As in real life, folks drafting behind me, but I tend to get very little benefit.

Dan
Dan
1 year ago

sticky drafts can also hinder you.. bigger/heavier guys cause more sticky on a smaller/light rider as you’re trying to get by them. that can be frustrating.

Matt
Matt
1 year ago

From how does Zwift calculate my speed…
“Weight: lighter riders will go faster on flats and climbs than heavier riders if both are putting out the same wattage. Heavier riders will descend faster.”

Curtis Repen
Curtis Repen (@crepen)
1 year ago
Reply to  Matt

Matt – Exactly. Same “wattage”. Same wattage for lighter rider means higher watts/kg. At same watts/kg, heavier rider puts out more wattage.

Matt
Matt
1 year ago

On a separate note, Zwift speeds are greatly inflated on flat/rolling terrain for all height/weight groups.

Joe
Joe
1 year ago
Reply to  Eric Schlange

I disagree as well, on my TT bike I can go sub 55 for 40K on ~270 watts at 6′ 3″ and 190#’s. On my Zwift TT bike I can’t go nearly that fast on 270 watts.

Dan
Dan
1 year ago
Reply to  Matt

YES it is Matt. Ive seen people brag about their times with zwift on Strava… hahahahahaha the speeds are greatly exaggerated. In relation to each other in the game, it doesnt matter.

Dan Connelly
Dan Connelly
5 months ago
Reply to  Matt

Most recreations riders pay no attention to wind resistance and ride too upright (especially head), with baggy clothing. Zwift assumes pro-like positions. Pros use form-fitting clothing and keep their heads down. Also pros tend to use the best tires, often with latex tubes, at optimal pressure and thus have lower rolling resistance. There’s also drive train losses but for a smart trainer these come before power is measured so that’s taken care of.

Joe
Joe
1 year ago

This explains a lot, thanks!

I feel like even getting 1/2 way back in a pack is harder than near the front…is this just my imagination? On group rides my motto is “never behind the beacon!”

Terry Ritter
1 year ago
Reply to  Joe

Half way back should be BETTER than being near the front, at least as far as draft. It is a bit harder to gauge the surges at the front half way back, and I like to pay attention to the structure of the group (3 abreast versus strung out, for example) and the watts/kg numbers the lead riders are doing to get a heads up if it’s about to get fast or not and push early to keep my position.

Oli Kratz
Oli Kratz
1 year ago

hi, so far so good but what I don t understand is why Zwift doesn’t include the cadence into the calculation which easily could have been taken into account from an arithmetic perspective. Going with 60 rpm by 3w/kg compared to 100 rpm with the same w/kg should be a significant difference … but not in Zwift ?!? Many thanks, Oli

Rusty
Rusty
1 year ago

Sorry but the view that lighter riders will suddenly shoot off the front on hills is just wrong. I tested w/kg in March of last year and it fits with what is predicted: the heavier rider is faster, everywhere. HOWEVER, the difference is GREATER going uphill compared to flat.
https://docs.google.com/spreadsheets/d/13YWcTVAf2bDzeDqVIq_HullSgh1HLarQFg7Qyi5bFrw/edit?usp=sharing
Add this to the fact drafting impact will be less due to low speeds, then the advantage in a race/ride will likely be even greater.
This is why when it gets steep, guys like Ollie Jones and Alex West are absolute machines!

Jeff slater
Jeff slater
1 year ago
Reply to  Rusty

How do you explain the lighter riders in real life pro races going off the front up the hills and dropping the heavier ones behind?

Rusty
Rusty
1 year ago
Reply to  Jeff slater

IRL the difference should be least going uphill, but they are still technically faster given ideal conditions.

Geoff
Geoff
1 year ago
Reply to  Jeff slater

Jeff. This is easy to explain. The lighter riders that excel going up hills IRL have a higher w/kg than the other rides. What so many people seem to forget is that zwift races are categorized by w/kg. When going uphills the light and heavy riders are more or less fairly matched because w/kg matters more than pure watts and the light and heavy riders have a similar w/kg. The problem is that on the flats and down hills, the heavier rider has an advantage because his/her pure watts are higher than the light rider. So, the difference is that… Read more »

Jonasty
Jonasty
1 year ago
Reply to  Eric Schlange

Just curious, your saying a heavier rider will go faster with the same w/kg as a lighter rider on the flats. But the opposite on the hills. So at some point the switch happens, and at what grade hill that happens depends on the difference between the two riders. Correct? Is there a median grade where this happens? Or is it the same point, but more extreme difference on either end?

Jonasty
Jonasty
1 year ago
Reply to  Eric Schlange

OK, makes sense now that I think of it. Thanks for the quick response.

Rusty
Rusty
1 year ago
Reply to  Eric Schlange

Hang on @misc , most of what you just said is what I was trying to say. For the Epic KOM (10km 3.9%), for every 10kg increase (at same w/kg) you go about 1.2% faster – (with diminishing returns at high kg) For the Radio Tower (1km 13%), the difference is about 1.8% faster for every 10kg (faster drop off curve) This is compared to the flat of approx 0.9% increments. So yes, as it gets steeper heavier riders do go relatively faster. This is not what happens IRL or what happens using http://bikecalculator.com/ this is because the normal force… Read more »

Dan Connelly
Dan Connelly
5 months ago
Reply to  Rusty

This is completely the fault of a highly flawed category system. Instead of rating on W/kg, they could use a fixed wattage + W/kg, which would compensate lighter riders for their relatively higher wind resistance / kg.

Ulf Rydberg
Member
Ulf Rydberg (@ulf_rydberg)
1 year ago

One thing not mentioned is that the categories and also the shown W/kg in Zwift is your power divided by your body weight but the speed calculation is based upon your power divided by your body + equipment weight. For example at 3.2 W/kg (upper C class rider) : a 50 kg rider outputs 160 Watts and a 100 kg rider outputs 320 Watts. If the weight of the bike is 8 kg, this gives an effective W/kg of 160/(50+8) = 2.76 W/kg for the 50 kg rider and 320/(100+8) = 2.96 W/kg for the 100 kg rider. That’s a… Read more »

Joe
Joe
5 months ago
Reply to  Ulf Rydberg

Finally, an intelligent response! Hey I’m wondering….is the draft behind a big rider more than a smaller rider? Because IRL rides smaller guys tucking behind big guys save a huge amount of energy. If it’s a standard amount in zwift then the smaller guys might be feeling more wind than IRL. If this is so I stay tough luck, try drafting a skinny 130 pound guy when you weigh 200 IRL 😉

Ferellie
Ferellie
1 year ago

So does this mean that as a 62kg rider entering a B or C race I cannot win because if a heavier rider averages the top end of w/kg allowed the only way I can beat him is to exceed this and be disqualified!

Geoff
Geoff
1 year ago
Reply to  Eric Schlange

Eric,. I’m betting you wouldn’t be so dismissive if you were a light weight rider. Don’t heavy and light riders have a more or less equal playing field on the uphill races in zwift? Aren’t light and heavy riders equally matched on uphill zwift races which are based on W/kg categories? If that’s the case, you should have a chance to win uphill races while the light rider has little/no chance of winning the flat races. Shouldn’t light riders be able to have a chance at winning a flat race on zwift? We all pay the same fee. In real… Read more »

Joe
Joe
5 months ago
Reply to  Geoff

I’ve been on the ropes for 30 years when light guys pin it on the climbs….finally in Zwift I feel like I can do some damage.

Noel Slevin
2 months ago
Reply to  Joe

This is my experience too. I’m 180cm, 65kg, put out just shy of 4.0w/kg. In the real world, I can’t keep up on the flat, but I can tear people apart up a climb. On Zwift, it’s almost the opposite. I’m working hard to keep up on the flat, then I get to the climbs and… they pull away? Even when I’m pulling over 5.0w/kg I struggle sometimes. In the real world, if I’m still with them at the bottom of a climb, there’s no chance they’re with me at the top. It’s the one thing I’m really good at… Read more »

Andy
Andy (@arjenner78)
1 year ago
Reply to  Eric Schlange

Erm no Eric I disagree with your second point. Not if you are an 80kg 3.99w/kg B. You will go the same speed as a lighter B rider up the climb at the same W/KG and have an easier time on the decent and flat. For a lighter rider to beat you they will exceed w/kg limits and get DQ/upgraded. W/KG categories and Zwift displaying other riders make us concentrate on w/kg as some sort of leveller and it is not. The raw watts criteria for upgrades really does not kick in until you are sub 60kg.

Rob Scott
Rob Scott
1 year ago

Perhaps though, Zwift doesn’t emulate physics so well. In the real world, heavier riders have a larger frontal area and unless Zwift takes into account height and weight to attempt a frontal surface area, it won’t calculate drag properly.

Andy
Andy (@arjenner78)
1 year ago
Reply to  Eric Schlange

Yes Zwift might emulate psychics well but Zwift/ZwiftPower does not mimic IRL ranking/categories well. Which is the issue with such a concentration on w/kg. I think points you yourself made in tour articles about esport and racing improvements

Marcus
Marcus
1 year ago

Zwift really does show mercy for heavier riders. I’d say that they know from the huge database excactly who their average customer is and they want to give the majority a good feeling. Heavier riders are not penalized by weight on the hills the same way as outside. Take the Epic-Kom with 10k in Zwift: With 68 Kg and a not-so-bad FTP around 4w/kg I gain to a max 30 seconds against a 3,5er (e.g. 90kg) to the top, partly because most of the gap is closed over the rolling hills after tunnel. Those 30 seconds will turn to loss… Read more »

Joe
Joe
1 year ago
Reply to  Marcus

My prediction is we’ll start to see larger riders winning the big pro Zwift races. As we all know, 200+ pound guys have a tough time winning IRL. In every form of competition there is an ideal body size and type, virtual racing is no different and it’s nice for big guys to finally have a shot in cycling. Just my opinion…at 86kg LOL.

Jordi
Jordi
1 year ago
Reply to  Marcus

I’m a big guy and think you’re totally right that the courses on zwift favor big guys with big watts and the focus on W/kg is unfair for smaller riders. However it is also much harder for a big guy to get at the same W/kg as a smaller rider. Yes you’ve got more muscle mass when you’re big, but it doesn’t increase proportionally with height. (This actually makes it worse as you’re probably competing against guys that are a lot fitter) And lastly to comment on the smaller differences when climbing: trainer difficulty is key. On zwift I’m riding… Read more »

Flex Rampant
Flex Rampant
10 months ago
Reply to  Marcus

I totally agree.

Daryn cummings
Daryn cummings
1 year ago

Sorry your explanation make perfect sense, but I did a session I’m in the middle of the pack I’m reading 2.7 wig but everyone else is reading 1.3 to 1.7 ?

Reverz
Reverz
11 months ago

“And remember: you’ll get ’em in the hills!” — this is simply a false statement for every category except cat A and especially in cat C. It’s no coincidence that 9 out of the current top 10 cat C riders on zwiftpower are 85+kg (apart from the fact that half of em are sandbaggers, but that’s another discussion). A lighter rider has to ride on (or sometimes over) cat limits just to keep up with a bunch of “heavy weights” on flat sections and then when the road goes up a 60kg rider’s 3,2wkg makes them go uphill just as… Read more »

Tyler James
Active Member
Tyler James (@mrtyside)
11 months ago
Reply to  Reverz

This is so true! I’m a very small rider and I have to murder myself to keep up on flats, even though if you look at my w/kg I’m pushing up towards the top end of my category. Only chance I have are steep hills, which encompasses very few of the Zwift races and events. In real life I can hang much better on flats with larger riders.

Reverz
Reverz
11 months ago
Reply to  Eric Schlange

You make a good point in your last paragraph, about the larger number of heavier riders. I will however deny that lighter riders drop heavy riders uphill by default (in lower cats at least), simply because of cat restrictions being purely relative power based. Last year one of the top racers in cat C (100kg+) actually won an Alpe Du Zwift race in a pretty stacked field… why? Because he was riding exactly on the 3.2wkg limit uphill… meaning, regardless of weight, anyone riding uphill faster would be doing over 3.2wkg (3.2 is 3.2, 60kg or 90kg) and thus get… Read more »

Allan Spencer
Allan Spencer
11 months ago

Interesting stuff. using a similar example as the article only applying a 10% gradient rider A 60kg rider holding 240 watts travels at 11.21kph (4w/kg) and rider B 80kg rider holding 320 watts travels at 11.65kph also at 4/wkg (speeds taken from bikecalculator.com) . My takeaway is that regardless of terrain/gradient if 2 riders have the exact same W/kg the heavier rider will always be faster due to the “pure wattage”. This is what I struggle to understand as i always thought there would be a point in the hills when rider A would be more efficient. Can someone school… Read more »

Charles Handren
Charles Handren
9 months ago

Very helpful for Zwift and the road, thanks a lot for putting this together.

Michael Davis
Michael Davis
9 months ago

Are there riders who purposely lower their virtual weight outside of races so they can complete all the hilly Zwift routes much quicker and therefore get to higher levels faster in order to get better bikes and wheels. How could that be detected since it wouldn’t show up in ZwiftPower?

Gregor Berlisk
Gregor Berlisk
8 months ago

Hi Eric can you explaint this.
I was competing on TT race (TT bikes only) 17km there was 15 riders.
The avarge slope of the course was 0%.
I was the heaviest in the group. Mesauring the avarge power I was the 5th rider of the group.
At the end I was 13th of 15 riders. How come?
I was beaten by a rider who had 40w less average power on flat course??!!

Joe
Joe
8 months ago
Reply to  Gregor Berlisk

could possibly be when you apply the power, pushing hard on a descent and going really easy on a climb will result in a slower time

Joe
Joe
8 months ago
Reply to  Joe

Or going super hard for awhile then super easy for awhile, that will be slower on a flat course

timr
timr
8 months ago

I am a 195 lb guy. it still seems I do worse on the flats than on real roads. On really flat roads I am never dropped (until the first sign of a tiny rise). On Zwift I can have a much tougher time hanging with a strong group on the flats. Maybe my drafting style worse on Zwift?

Juanjo
Juanjo
8 months ago

Great post! But, how come I am beaten by a rider who has developed both fewer w/kg and total watage? It was mostly a flat route (6 laps around volcano) and I was not in the front group a lot. I made 284 vs 235 w and 4.44 vs 3.92 w/kg. Any explanation? Thanks!

Tobi McTobeface
Tobi McTobeface
8 months ago
Reply to  Juanjo

Normalized power between you read likely different. If you held a steady state 284 and the other rider hit the hills hard and then put in just enough to maintain speed then his average per would be less. NP would tell the better story. Average power tells you very little about the race.

Tobi McTobeface
Tobi McTobeface
8 months ago

Let’s not forget the physiological cost of a larger rider having to put out those higher watts requiring much more recovery time that a light rider putting out far less even at a higher wkg. Let’s not anyone mistakingly imagine that heavier guys are having an easy time on Zwift compared to light guys. 🙄 Already heard this in some quarters and them asking for tweaks to be made in their favour. Again.

Frank
Frank
8 months ago

Zwift show my power much lower than reality. Its a known issue because i use an old elite realaxiom wired trainer.
so if i intentionally drop my weight to reach my “real” W/kg, would this “cheat” allow me to follow riders in a fair way?

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