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.
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#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.
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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!
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..
Flattery will get you nowhere, sir!
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.
And yet, IRL we often excel at TTs
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.
6’2” and 174 lbs here. I do reasonably well on long climbs but get killed on flat courses.
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
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 the hill you rarely can catch back on, regardless of size due to the draft impact downhill.
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!
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???
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.
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.
That’s a unhealthy weight for your height bud.
Thank you Dr. Where did you go to medical school?
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 ?
Sure, those make an impact as well, especially if you’re comparing MTB to road bikes in the Jungle, for example.
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?
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.
its the speed they are travelling; when they are about behind you by 4-5 secs, click on any of them to see what speed they are travelling; then match it just before they catch you. – you will have to ride a LOT harder than they are to get on; then once you are there, settile in and rest back up
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?
There IS. We need to test it more to find out how much of a difference.
This is good to know. As in real life, folks drafting behind me, but I tend to get very little benefit.
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.
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.”
Matt – Exactly. Same “wattage”. Same wattage for lighter rider means higher watts/kg. At same watts/kg, heavier rider puts out more wattage.
lighter riders go slower than heavier on flats
On a separate note, Zwift speeds are greatly inflated on flat/rolling terrain for all height/weight groups.
I disagree. There are lots of variables in play–riders who compete outdoors with good equipment in very aero positions on smooth tarmac may find Zwift slower, while those who ride in a more upright position on poor roads with slow bikes will certainly find Zwift quite fast. Read more here: https://zwiftinsider.com/zwift-speeds/
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.
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.
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.
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!”
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.
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
Cadence doesn’t affect speed, so there’s no reason to include it in the calculation.
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!
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?
IRL the difference should be least going uphill, but they are still technically faster given ideal conditions.
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 in real life, race categories are based on abilities and on zwift, one is shoe horned into a category based purely on W/kg, putting light riders at a disadvantage that makes being competitive in their proper category next to impossible.
The difference is NOT greater on flats than hills. Your test numbers may be showing this, Rusty, due to the high wattage you used in the tests–on flat ground at high watts, speeds get closer together.
Also, steepness of the climb matters–the steeper the climb, the greater the difference will be between riders of different weights but same w/kg. Our tests were done on the Alpe.
Run the same test at 2, 3, or 4 w/kg and you’ll find the difference is greater on climbs… which is as it should be.
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?
I’m not saying that, @guest_29116.
At the same W/KG, the heavier rider will ALWAYS go faster. Because they’re putting out more watts, as well as overcoming gravity.
Conversely, at the same WATTS, the lighter rider will always go faster. Because they’re moving less weight.
(This is assuming everything else is equal, of course–same height, bike, etc).
OK, makes sense now that I think of it. Thanks for the quick response.
At the same W/KG a heavier rider should NOT go faster…. thats just scientifically stupid…. especially when you can assume they are likely to be less aerodynamic lol
Despite seeming scientifically stupid to you, in most situations, it’s true.
It may seem scientifically stupid to you, Dave… but it’s accurate. It’s physics.
Test it on an online bike calculator that estimates speed for various conditions… here’s one: http://bikecalculator.com/
This is a negative ghost rider. The pure watts still matter on climbs especially when they are less than 7-8%. It’s when the gradients start hitting 7-8% where mass becomes detrimental to maintain w/kg without going into the red too much. This is why you will see the better bigger riders attack the steepest slopes of the Watopia KOM forward and reverse viciously then settle back in, because trying to tempo can cause gaps when the grade reaches 10% by just a small change in cadence. As a bigger rider and a sprinters power profile I don’t do much racing on climbs longer than 5 minutes (Titans Grove Forward). The problem for bigger riders is steeper climbs require good cadence management to maintain speed and not go into the red too much. Also what many miss the point on is heavier riders have a harder time staying at the back or in the middle of the pack and the best bigger riders fit into at least one of these categories, they are excellent punchers/sprinters and/or they are efficient at pedaling. This is also the very reason why height and weight should be publicly available to all racers as it allows you as a competitor to visualize who you are racing against as you might do in real life.
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 vector angles further away as it gets steeper. The Normal force becomes less and less, the Weight force is the dominant force opposing movement. Heavy still dominates, but less pronounced.
The difference should be downhill>flat>uphill (the exact opposite to Zwift currently)
I chose 5w/kg because this is generally the minimum required to stay with an A cat race up a significant climb. When I have a spare 4 hours, I’ll try with a lower w/kg reference range. The percentage difference on the flat may increase, but I think the climbing times will increase further
@guest_29077 re #29154
That’s now what I’m seeing in my tests at all. And I’m talking about a LOT of tests. 😀
In my tests with riders at 50, 75, and 100kg, at 2, 3, and 4w/kg, the biggest % speed difference if you compare different weights but same w/kg is on the descent. Then the next biggest difference is flats, then climb. Which is as it should be.
This is how it’s always worked out in my tests, so I’m not sure what happened in yours–but I’m confident in my numbers.
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.
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 big difference.
That’s a great point, Ulf!
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 😉
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!
This is why ZwiftPower w/kg categories also include a raw wattage requirement, so lighter riders aren’t forced to upgrade.
Another way to look at it is this: you’ll have a hard time winning flat races, just like I (at 83kg) find it impossible to win climbing races. So enter the climbing races if you want to win, and I’ll enter the flat races if I want to win! Just like outside.
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 life, a light rider would have a very hard time at becoming a top level racer on flat, sprinty races or in Crits. However, in real life, a light rider can still race in lower categories of those types of races and have a chance.
Zwift should find a way so that all users can compete fairly and have a chance to at least be competitive in all types of racing. More fun for more people.
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.
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 on a bike. But not in Zwift.
Are you racing the same people in Zwift you are racing IRL?
Because I am the same type of rider, but I guess I am just meeting stronger riders in Zwift, who would also do well on the climbs IRL. Out on the road, I only meet few people, who will beat me on a climb, especially longer ones. But we also know that for some strange reason, a lot of people are much stronger riding indoors than outdoors… 😏
yeah the fatguys revenge :/
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.
I don’t disagree, @guest_29187 — your observations are spot on. The w/kg categorization system is far from perfect, and I’ve never said it works great.
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.
Zwift DOES take height and weight into account in order to calculate a CdA for each rider.
I’d say Zwift emulates real-world physics quite well.
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
I can believe that Zwift uses individual characteristics when computing our CdA, but I don’t find evidence for the same in how it determines the draft we provide. That is, our stats seem to determine how we accept draft, but not how we give it. I think this accounts for how, as a 58kg rider, my experience of riding with a single larger rider in Zwift is reversed from reality. IRL, an 80kg rider behind me on flats or downhills is often cursing because of the insignificant draft I provide, and practically towing me when our situations are reversed. In Zwift, by contrast, in a breakaway with another, larger rider on flat/rolling terrain, I observed that I was putting out roughly the same w/kg drafting as he was in front of me (both on Tron) – while behind me he was able to cruise at .3-.5 w/kg below my effort. And the disparity was exaggerated to near absurdity on descents. So … my experience suggests that Zwift emulates half of real-world physics quite well!
You’re not wrong, Wil 🙂 https://zwiftinsider.com/rider-size-draft/
You do great work, Eric – thank you! Does this make you think of including downhill data in your frame/wheel analysis (along with climbing and flats)? It’s tangential to this topic but might help illustrate for smaller riders the need to skew toward aerodynamics in equipment selection. Thanks again.
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 of 1 minute within 2k on the descent (yesterday we had riders managing red power numbers on the descent. How could that be on a smarttrainer?). The worst are the rolling hills in the jungle: I’ve never managed to hold the bigger boys there. Yesterday we were already 40k in the race and a front-group of ten, so you could tell that we were nearly equal, but suddenly 4 traveled away easily and without significant surging. And over 2k they gained 1 minute. I could complain about that, but I don’t. The overall experience, the social rides, the workouts and the ability to race savely in Zwift weights much more for me. Just take the fun out of it.
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.
LOL–I wouldn’t hold my breath!
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 up a hill/mountain with 90rpm whereas in real life I’m happy to spin 75rpm. This means I’m using more of the cardiovascular system and less muscular power, which translates to being less fatigued and keeping my power longer. (This doesn’t hold up if you’ve got a crazy big sprocket on the back when you’re outside)
I totally agree.
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 ?
“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 hard as a 90kg 3,2wkg. To be honest, if the road’s not steep enough the 90kg rider is probably still at an advantage…
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.
My observation: for every lightweight rider complaining about the flats, there’s a heavy rider complaining about the climbs. Just like outdoors. 😀
@guest_31423: I don’t think my statement is false at all. The reason the top C riders are heavier is because most of the races are on flat courses! But if you look at race results for “climby” races, the lighter riders win.
Also–saying “you’ll get ’em in the hills” doesn’t mean you’ll win the race. There are a lot of variables in play here, but you can’t deny that lighter riders generally drop heavier riders on climbs. Now, whether you can stay away and win… well, that’s another topic!
Lastly: I don’t have the data to prove this, but my guess is the lower categories (D and C) skew much heavier in terms of body weight than A and B… just like outdoors. So you’ll find more heavy riders winning races.
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 bumped up to cat B.
From my experience as a cat C racer (being on the heavier side myself) it’s mostly heavier riders winning, even on hilltop finishes, even when there’s a fair representation of lighter riders.
In any race that is a closed circuit, there will be as much uphill as downhill so that evens out imo. Since my downhill disadvantage is much bigger than my uphill advantage in most races i most of the time ride alone at the end, just to complete the race.
Im a light rider and in every cat C, I’ll have to work hard on climbs but have a small advantage, work VERY HARD on flats and then get totally dropped at the downhills no matter how hard I dig, can’t even remain in the draft, and once they’re gone, I never see them again 😁
According to zwiftpower I should be a B rider based on FTP and wattage but I’m humiliated in C always getting dropped 🤣
Only race I can survive is the races without uphills, because then there’s no downhills ✌
Like yesterday in a social cat C group ride “Sunday Climbers” one would think I would survive. After first lap and first long downhill…bye bye
in this moment in the top ten cat c, 6 (2-3-4-5-6-10) are under 50kg😀
in this moment in top 10 cat C, 6 (2-3-4-5-6-10) are under 50kg
At one point they implemented absolute power restrictions which were primarly ment to make “regular” lighter riders (55-60kg) more competitive. Which is something that imo never worked, not even a little. They were still being roasted.
However, meanwhile quite a few juniors seem to have taken up Zwift. These guys weigh under 45kg. There even was a 9-year old French kid this winter weighing in at just 26kg… he was doing 125W and simply wrecking the field at ~5w/kg. It’s a massive gaping hole in the current cat system…
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 me please. Allan
Rider A IS more efficient, in your example. 240w is a lot less than 320w. (I know you meant w/kg efficiency, but I’m trying to make a point.)
There’s a reason why you don’t see many 80kg riders winning mountain stages IRL. Their bodies just can’t sustain the crazy w/kg needed to do so. But 60kg riders can!
Very helpful for Zwift and the road, thanks a lot for putting this together.
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?
That’s what I was suspecting before reading this article (that other riders were lowering their virtual weight to get a better w/kg).
I have come to the conclusion that I should just ride my own ride and not get stressed about others, since I’m not racing them (e.g. Tour of Watopia). I’m doing it because I enjoy it and it’s a good and safe workout. I don’t care if others are maintaining the same speed at a lower w/kg than me – good on them for being a stronger (heavier?) rider than me. 🙂
Also, on a separate note: at the end of the day, those riders who are lowering their virtual weight (or cheating in other ways) are just lying to themselves, and they’ll be very disheartened when they actually go outside for a ride and aren’t putting out anywhere near their numbers on Zwift…
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??!!
If the course was truly flat, then my explanation would be that you’re much TALLER than the other riders. Height makes a big speed difference in Zwift. https://zwiftinsider.com/how-height-affects-speed-in-zwift/
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
Or going super hard for awhile then super easy for awhile, that will be slower on a flat course
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?
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!
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.
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.
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?
Section: One-two punch
There is a bug:
“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 should be:
“let’s say you are a 60kg rider racing in a pack being pulled by a 78kg rider who is putting out 312w (4w/kg). The pack would be traveling at 40.6kph. Since you are drafting, you only need to put out 75% of the 312w”
No, I don’t think so. I believe it’s accurate as written.
So in that case, I’m not getting that sentence: “Since you are drafting, you only need to put out 75% of the 312w”. Where did you get 31w from?
*312w from
On the lines above you are comparing to the leader of the pack who is rifing with 360w.
I thought I would get any rational answer but unfortunately I didn’t.
Sorry – I get hundreds of comments a day. Can’t always respond. Yours got buried.
The 312w is what “it would take you to travel that same speed solo”, as I said above. That’s based on the kreuzotter.de calculator used throughout the article.
You also forgot to mention different trainers will produce different wattages. The ZPOWER should be completely outlawed IMO. Also wheel on trainers such as Vortex are not nearly as accurate as the direct drives.
No, I didn’t forget! What you mention (trainer accuracy) is a totally separate issue that I didn’t want to get into in this post…
Fair enough. I look forward to a post on that. Thanks Eric! 🙂
I am 85kgs and yesterday did a 16kms individual TT through the desert holding 357watts, but got overtaken and beaten by 18 seconds by a 60kgs rider putting out 289watts. We had the same kit – best TT bike, zipp 858 wheels, and as it was an it there was no drafting. That just isn’t realistic- bikecalculator suggests I should have beaten him by over a minute. As Zwift is systematically biased against bigger riders, it effectively encourages dishonesty about weight and height.
Old post but I think it totally makes sense you were beaten by the lighter rider – who was averaging 4.8 w/kg to your 4.2. In fact, I could see how that rider would feel this was an example of game bias toward a heavier rider if they only beat you by 18 seconds when averaging so much more power.
Thanks. That explains a lot why I’m, as a women, often having a hard time in mixed groups. I’m very confused when looking at the w/kg of the others around me why I’m struggling that much.
I’m not a super light-weighted XXS-women so I never referred to myself as a “light rider”. But if 60kg is light, so am I.
Climbs are the place where I can easily push to the front of a group. And I have to – because I’m loosing my position on the descent anyway, or have to continue my effort while everyone is resting.
I usually prefer the banter of mixed groups over pure girl’s chit chat, but to chose a group ride by what w/kg I would like to ride that day is way more reliable with women-only rides.
Additionally, in big groups I experience to get crowded out or bumped into the back until I get spit out of the group if I’m not putting out a lot more w/kg. Very stressful.
Is that an effect of being lighter, too?
Sadly that forces me into being a flyer. The safest place is near or ahead of the fence.
But all this complaining should not cover the fact that “having a hard time” = GAINS 🤗
One factor that gets overlooked when talking about power to weight ratio (w/kg) and climbing performance is the contribution of the bicycle. The power to weight ratio that Zwift reports to you is your power output divided by your body weight. The rate of climb that you can achieve on a steep hill is determined by your power divided by the total weight of rider plus bicycle, just as it is in the real world. In the real world, smaller bicycles ridden by smaller people weigh less than larger bicycles ridden by larger people. It is not apparent whether Zwift accounts for this in their physics model. It is also not obvious to most people that bicycle weight generally penalizes smaller riders more than bigger ones, because bicycle weight does not scale in direct proportion with body weight. Therefore the bicycle weight generally becomes a larger portion of the total weight the smaller the rider is, even if smaller bicycles are allowed for.
Even in climbing, a heavier rider needs less W/kg than a lighter rider. Because bike weighs the same, lighter rider must generate higher w/kg so their power to total weight ratio is the same as heavier riders’. Lucky for us, bikes in Zwift are ridiculously light, so this effect are less pronounced than IRL. My time up ADZ is 44:51 with 252W avg power, weight setting is 56kg. Based on this I calculated that the total weight of rider’s clothing, a bottle of water, Tarmac Pro and Lightweight Wheel is only around 3.5kg!
Then again, IRL if you are a light rider live in a flat country, your W/kg is usually way higher than your heavier riding buddies so that you can keep up with them.
One of our event leaders was supposed to ride between 1.3 and 1.7 w/kg. He’s my age and about the same size as me. After a 55 minute ride, I was probably 2 miles behind him and I kept at between 1.5 and 2.3 w/kg on a flat course. I’m not sure Zwift has this thing right at all.
Hi. Given all the algorithm changes that have occurred regarding drafting, can you update the examples in this article? I understood and experienced drafting as explained by the examples. I didn’t like it but I could deal. Now I find myself sitting in a field pushing even higher watts than I used to. It’s one thing to have the draft advantage cancelled due to my lower weight, but now it seems I have to push even higher watts to stay in the field, pushing me to do 0.2-0.5 w/kg more than those are around me. Why? 😭
how can 2 people with a difference of 20 kg do the same race finish with the same time give or take a couple of seconds finish with the same watts ?
Drafting.
Great information. Question: At 60 kg, I seem to have to do 4w/kg to match the speed of my 78 kg, up hill at 8%, he’s only doing 3.5w/kg! I knew this woukd be true on the flat, but didn’t expect it uphill?
Thank you, great info on how to race more strategically.
Another question, does it help to do short bursts of high w/kg . . . that was one area where I had lower w/kg in the 15 second column and the 1 second column. Is there a strategy to this?