Just raw watts, not watts/kg.
A not all riders of different weights do the same wattage on a flat road. A lighter rider need less power than a heavy rider to maintain the same speed on a flat road. For instance a 1.7m 65kg rider has to do 240w to maintain 32km/h where a 1.85m 100kg rider has to do about 295w to maintain 32km/h
This is because rolling resistance is effected by weight and drag by the size of the rider and usually as they get heavier they get taller and wider.
I used Bicycle Speed (Velocity) And Power Calculator to calculate speed, zwift use similar formulas.
So yes the current system only divide riders into weight classes (except for the alpe).
Racing ranking is needed to make it more competitive and fun.
That’s interesting, thanks Gerrie: I hadn’t realised that the Zwift algorithm takes height/weight into account when calculating drag. I had a play around with the website to see the effect of varying height and weight on the drag and it seems weight has a bigger impact than height, which I guess makes sense if one is on the drops (which is the option I clicked) I had a little play around with the result from a recent flat race i did and that does confirm that weight and average watts are correlated to some extent. I think my point still remains valid though (admittedly rather less starkly than before): using the speed/power website calculator for a 175cm 65kg rider and a 185 85kg rider, both riding at 35kmh, the lighter rider will need 214W, the heavier 240W, so the lighter rider will be doing 3.30 w/kg and be disqualified if he entered a C cat race whereas the heavier one is fine at 2.82 w/kg. I think my idea of raising the FTP level at which one gets moved up still works but the level probably ought to be more like 235-240W for a C to B.
Having said all that race ranking is the way to go, I just don’t understand why it isn’t being implemented and am assuming there must be some technical difficulty
The height of a rider has a big impact on speed in zwift as well. There are a few good youtube videos which highlight this - Chris Pritchard did a good one comparing different heights of avatars with the same weight on zwift riding the same number of watts. Key takeaway was it makes a bigger difference being shorter than if a rider is a few kgs lighter.
Thanks Bella that’s interesting and suggests the algorithm is a bit different than the one on website that Gerry kindly pointed us to. Maybe that is closer to real life that being skinny and tall is a bit of a disadvantage when racing on the flat. I recall that Cav said (when he was still winning races…) that being short was a big advantage for him in the sprint.
I wish they would fine-tune this a bit more. Do they assume the taller rider always rides in a fully upright position all the time?
As a tall rider, it’s been a real struggle to be competitive in races knowing I am severely penalized for my height.
My general sense is that height doesnt make THAT much difference on the road. Rouleurs are often big guys - look at Indurain. I get it about smaller sprinters, but theyre basically a different species from the rest of us. And climbers - usually smaller people - and thats all about weight and power, really - isnt it? Anybody know what the data is for this issue on the road, and how that compares with the handicap Zwift uses? Quick solution - everybody on Zwift just puts in that they are something like 5’8" tall…
The method by which Zwift calculates and reports W/kg on-screen (and in ZwiftPower) has other problems which you may not have taken into account. It basically comes down to proportionality. Zwift does NOT take into account the various riders’ equipment selections, at least with respect to displaying W/kg.
This failure (feature?) results in flawed Power/Speed comparisons. Here’s a simplified example for you to consider:
Height 180 cm
Weight 80 kg
Bicycle weight 10 kg
Wind speed : 0
To produce a speed of 37kph, according to the referenced calculator, Zwift would advise us that the rider needs to produce 230 watts or 2.55W/kg when excluding the weight of the bicycle. INCLUDING the weight of the bicycle, this is 2.875W/kg. A substantial difference in using the W/kg method for the same rider. But the difference between different rider morphologies is even more stark…
Height 170 cm
Weight 70 kg
Bicycle weight 10 kg
Wind speed : 0
Now, let’s take the smaller rider spec’d above, attempting to match speeds on the basis of W/kg as used by Zwift. To produce the same speed of 37kph, the calculator advises us that the rider needs to produce only 216W. Zwift would report that rider as producing 2.7W/kg. However, in reality, that same lighter rider actually needs to produce 3.09W/kg when taking the weight of the SAME bicycle into account.
Very simply, W/kg is a fairly good metric : when it takes the total weight of the cyclist AND her equipment into account, and produces distorted outcomes when it excludes the weight of the equipment selection. This became hilariously evident in a recent Zwift event in which riders traversing the same gravel route, using a gravel bike vs a “Tron”, were producing the same speeds, but with vastly different W/kg metrics. The equipment selection matters, and perhaps it should not be ignored in the W/kg calculations. Bottom line: a 10kg bike is a much larger (14.3%) percentage of a 70kg rider’s weight than that of an 80kg racer’s weight (12.5%) and in racing terms, what racer wouldn’t want to have a 2% advantage hard-coded?
Interesting stuff - any idea why Zwift doesnt calculate the weight of the bike? (Too many variables and hence data to manage?) Ive noticed this when people who are generating noticeably less “published” watts go cruising by me at considerable delta speed. So, bike weight REALLY matters - huh? How much does the Tron weigh?
In the particular example I cited, the variance in power output (which I observed to be about 0.5W/kg for an “average” rider), concerned rolling resistance rather than frame weights. So, NO, Zwift is not only already fully capable of managing these variables, they do it every moment of every day already. It’s just that W/kg is presently divided by rider submitted rider weight, not rider weight + frame weight. That’s why you see articles like this gain so many views:
Obviously Zwift “knows” the weight of each frame and wheelset (they don’t yet take account of helmets etc) available on Zwift. The calculation is no more intensive than the one they are performing now. It’s just a different view of W/kg. So when a runner laughingly passes me when I am pedalling a 50 pound “Citibike” up Harlem Hill in Manhattan, I often console myself knowing that he might not be so smug, if he were carrying my bike on his shoulders! And I soon warp past him on the other side. LOL.
You have to remember Zwift is not meant to be a ride simulator.
It’s close but when Zwift came out, there was no similar game that let us interact with each other.
The only alternative was to stare at the wall, watch tv shows or watch a non interactive biking film.
The calculations are close but not spot on.
I hope they apply their resources in other organizational ways.
The game, as is, is fine.
We need to clean up the cats etc.
I wish there was less emphasis on the drop shop.
I like that different wheels and frames give different qualities.
I wish there where more courses that emphasized those variances.
Right now I use my Tron, Tarmac Pro and MTB. I wish I had a reason to use my other frames.
And Zwift shouldn’t take it into account we don’t do that out side in the real world . W/kg is your wattage devided by your weight.
w/kg is only useful on climbs with gradients above 5%. That is how it came to be in real life (IRL). We use w/kg to compare climbing power.
For racing w/kg is just weight classes.
Please: tell that to the hundreds of thousands of racers in Zwift, that the racing categories having nothing to do with watts per kilogram, but rather “just weight classes”. You might find yourself in a bit of a pickle. LOL.
The expression “that’s the way it’s always been done before” is self-evidently an obstacle to progress and enlightenment. As Ayn Rand famously repeated, “Check your premises”. If your premise is based on some variation of “that’s they way we do it IRL”, perhaps your premise is flawed? Let’s just acknowledge that there are differing ways of examining the W/kg / weight / velocity issue, and be prepared to change your mind. Remember how many professional racers were blown away in the their first Zwift races? Things in Zwift are slightly different than in the real world.
Incidentally, it occurs to me that users of this forum do a disservice to the quality of the overall content when “quoting” someone completely out of context… This is a “fake news” technique that should be avoided in the interests of honest discourse.
For the record, what I said above, in full context, is as follows:
There, the context of my single sentence assertion is now included in its entirety, rather than a self-serving extract with differing meaning…
The topic of units of energy expended per unit of time in relation to rider mass (total mass or body mass?) and speed is clearly open for active debate, which is occurring in many threads in this forum and elsewhere. But let’s keep the debate honest.
I’ve acknowledged how Zwift calculates W/kg. I’ve merely opened the eyes of some readers to the fact that there are different methodologies (based in the actual physics of motion) for examining the issue that should be considered. Saying the earth is flat, and the center of the solar system, or at least that it SHOULD be so, does not make it so.
If all race courses were as flat as a drag race track, then a focus on straight, nominal power curves without reference to body mass/composition might have some merit. However, and thankfully, the classic bicycling racecourses (both IRL and virtual) have more interesting terrain geometry. Climbing (and not just 5% gradients and above) and descending are a huge, pivotal and exciting part of racing.
That said, I fully support results and performance-based racing classifications. Competency, results, and merit are the hallmarks of not just sports achievements, but arguably all achievement. As long as Zwift is applying the gross measurement methodologies currently in use, there will be debate about its relative merits as an effective tool for delineating race classifications. Whiney threads in this forum with some variation of “(anti-)sandbagging” and “I’m in the wrong category” are as common as complaints about missing route badges and hardware issues.
At present, Zwift (and ZwiftPower by extension) places a 63 year old, 78kg, 180cm, 245W FTP cyclist with 12% body fat on the same starting line with a 25 year old 68kg, 170cm, 211W FTP cyclist with 8% body fat and says, GO GO GO! LOL. There’s room for improvement! Open, honest and probative discussion will help lead the way to such improvements.
Why You Should Focus on Watts per Kilogram, by Taylor THOMAS
SPEED TESTS: STEADY W/KG ACROSS VARIOUS BODY WEIGHTS | Mar 19, 2020 |
HOW RIDER WEIGHT AFFECTS SPEED ON ZWIFT | Jan 16, 2020 | Speed Tests |
Power-to-weight ratio explained: why W/kg is important and how to improve yours Power-to-weight ratio explained: why W/kg is important and how to improve yours - BikeRadar
Power to weight ratio is important yes. But using it to classify riders is basically just putting them in wieght classes. The heavy riders can do higher wattage and still stay in the same w/kg class than a lightweight rider especially with most races being flat.
Let’s quote this.
As I said above and in the articles that you quoted, no one use weight including equipment when you quote your ftp in w/kg you devide it by your weight not adding the bike that you ride or if you have full or empty water bottles. That is how the coaches, pro’s and cycling community used it for decades.
Clearly, you didn’t read the quoted articles very closely…
But why is it that when two riders are holding the same w/kg, the heavier rider will always be faster? There are multiple reasons, actually–but one big reason is what we’ll call “true w/kg”–that is, including the weight of the bike in our w/kg number. Suppose we have two riders, 100kg and 50kg, both riding at 3w/kg. But let’s say they’re on 9kg bikes. If you add that bike weight to the rider’s weight and calculate the true w/kg, you get this: 100kg rider + 9kg bike @ 300 watts = 2.75w/kg 50kg rider + 9kg bike @150 watts = 2.54w/kg So even though both riders are holding 3w/kg, the heavier rider is holding a higher true w/kg.
Clearly “True W/kg” is a thing!
And you chose to ignore one of the articles you cited that clearly states:
How Do I Train It?
You’ll first want to calculate your power to weight >ratio for a given range. To do this, divide your body >weight in kilograms (1kg = 2.2 lbs) into average >watts for a given range.
It doesn’t talk about adding equipment weight etc into the calculation for w/kg.
I could be wrong, but I believe part of the issue is @Gerrie_Delport_ODZ is talking about how w/kg was created and used IRL and you are applying that IRL metric to the Zwift world which doesn’t 100% correspond to IRL cycling. It’s one of the reasons why many have argued Zwift needs to go to a points or classification system for racing.
Additionally, the “true w/kg” part quoted from Zwift Insider would almost 100% not be a factor IRL (where the w/kg metric was created) as pros would all be on bikes that weigh the UCI minimum and I have never seen a 100kg rider hanging anywhere near a 50kg rider on a climb IRL. That is something only seen in the fantasy world of Zwift.
Something tells me this conversation has just gone on too long , another side effect of Zwift , since they are now custodians of the platform used to define category’s , taking so long to move the current problem on from what might have been a quick and dirty way to get some sort of reasonably sensible grouping up of riders into racing categories.
I am sure you are all having a lot of fun debating the nuances of power and weight as it affects cycling but lets not get distracted with sideshows . The subject here is racing classification , event though it did start off on the is it w/kg or just weight , . ts pretty clear that neither is fit for this purpose and the whole area needs to mature now that we have (in theory) better data modeling and a clear appetite from participants , and hopefully owners , to do so , and a more mature product to work with it …
There really is only one solution here which is how every single competitive sport , without exception , works , your categorization needs to be based on results*. Whatever way you slice it until that happens the outcome , in particular as you move down the divisions , is dis-satisfactory outcomes.
- And in case anyone wants to introduce age group and indeed gender , for sure you can apply other things on top , but once you do that the division and only parameter used to rank is results.
I agree with Graham here that essentially what is needed is a revamp of the race classification system and as he points out this is an oft repeated thread. Does anyone out there (even better from Zwift HQ) know if progress has been made on this and whether there is any imminent plan to do anything? The cynic in me says that since Zwift is still in #1 position in the market and still gaining new customers (and don’t get me wrong, I do really like it especially when compared to the old style turbo sessions we used to have to do) that they feel they don’t need to spend the money to change. I did try contacting Zwift HQ direct to try and find out but got redirected back here!