W/Kg units, why this metric?
 

I am not fully clear regarding this metric used. i don't race but i do see the race categories in zwift and they are separated by a W/Kg range. i get that it is power divided by weight but it seems a bit abstract to me. let's say a big man generating a lot of power has a value of 3.0 w/kg and a twig like rider also has a value of 3.0 w/kg. will these two extremes perform about the same regardless of terrain?

while riding zwift (and i know it is imaginary and rife with cheaters) i occasionally see someone blow past me with a much lower W/Kg that myself, it is puzzling at times.

On flats, pure watts is generally going to go faster, going 280w at 4w/kg is going to be faster than someone at 220 and 4.5w/kg, but on hills the person going 220 at 4.5w/kg is going to get up the hill faster. So it ultimately depends on the course profile and the type of rider it'll favor

Some of those are just morons like me with a dumb trainer.

The W/kg is an attempt to normalize for body size differences. If I weigh in at twice your weight, it takes me twice as much power to climb the same hill as you do (in the same amount of time).

dial your "weight" back by 65% in the profile & go hunting for a KOM.

For similar (high) levels of athletic training, W/kg scales at less than the first power of mass, while (as you say) climbing work scales linearly with mass, so smaller athletes are advantaged in climbing.

Otto

I didn't know that. I just blamed it on being too fat, too old and too weak.

I suspect neither of us is in a fitness regime lofty enough to worry about this factor. I know I have some considerable room for improvement on W/kg, if I were interested, even considering my antiquity. I ride SS, so as long as I can climb and handle headwinds, all is good. :)

Otto

My biggest problem is in the denominator.

But of course body weight, as it's added to a human, doesn't all end up in parts that actually help with cycling. Why wouldn't Zwift just auto-place participants in the appropriate categories (not defined by w/kg) based on their past Zwift performances.. there should be a way will all of the speed, watts, terrain specifics to do this. Eg. how do cyclists get put into Cat1, 2, 3, etc?

All Zwift knows is your power output. Everything that happens within the program is based on that and whatever information you provide about yourself. The only way to try and make it a realistic simulation of how you normally ride is to use information such as w/kg. Using something like speed or whatever you mean by terrain specifics doesn't work unless you try to use something like w/kg to normalize performance.

i'd agree with better categorization for races in zwift. i tried one once. i put myself into cat C because i was border line C/B. when i did the race i was dropped almost immediately, it was really quite ridiculous, not fun at all. have not tried it since. i also think the cats are too broad.

You may have tried in the wrong race. The WTRL TTT and series races use a system that verifies through ZwiftPower dot com and enforces the rules. Its working very well as evidenced by the number of racers entering the races and lack of "sandbagging" claims being made that are so prevalent in other races.

Maybe they should have watts based racing and avoid the possibility of scale doping.

Right. So Zwift has your power output. But they also have, if you have any past history on the platform, how you performed using the power you had. I guess I'm wondering why Zwift just doesn't assign each person a category based on that?

TBH, I've always felt this is a tough one to fix but a key problem in Zwift. In the real world, it isn't just w/kg but also watts and aero.

I simply don't agree that Zwift chooses to "roughly" apply the same CdA to really large riders as they do smaller riders. If they do apply a different and less advantageous CdA to larger riders, it isn't how it works out in the real world. Meaning, the sliding scale should be more aggressive. As in it isn't believable whatsoever.

You simply can't ride a road bike looking like Eddie in the hour record the same way at 210lb as someone at 150lb can.

But only so much they can do. People already can cheat on their weight. Folks would cheat on this also by lowering their weight or height to get a lower CdA. If they went super detail oriented and had you measure your bike fit and put the reach, stack, etc... into your profile.............people would figure out how to cheat that also by lowering the stack height.

So, I take it "as-is".

It's gamified riding. So, we're bound to encounter similar things as in video games.

Yeah, but it's watts/drag which, given similar on-bike position, is going to scale differently than w/kg. So the bigger person making more absolute power will have increased frontal area and drag, but it'll increase at a much lower rate. Think of a 2x2x2 cube vs a 3x3x3 cube - the volume of the 3x cube is 3.375 times greater (27 vs 8), but the frontal area (one face) is only 2.25 times greater (9 vs 4).

Zwift owns zwiftpower. If they wanted to, they could do a mandatory placement of racers into categories by zwiftpower rankings (those 0-600 points things) and end sandbagging. But they don't because they think it will hurt their subscriptions when sandbaggers find out they can't sandbag races anymore and drop their subscriptions. They know most of us honest racers are delusional/addicted enough to come back regardless.

Or the Tuesday ZRL series.

I don't think CDA is really a thing in zwift, but yeah there is that

Changes in height have a pretty drastic effect in Zwift, so I hear.

factor in the group set combo being used, seat height, rubber resistance, & carrying load (water bottles) it would seem that the program couldn't know where to stop tracking your data.

I've heard this too. Someone on this board in another thread was posting about how they changed their height to 3ft and their top speed on descents went through the roof.

Do big e-races verify height? I know some have on-camera weigh-in requirements.

Based on my ftp I'm just under 3.1 w/kg. I do a few races not a lot and not well advertised races and I'm not even remotely a "racer". But I race in C class and my ZwiftPower results usually come in with a race average of about 3 w/kg.

Still, I get my ass handed to me all the time. Where I'm at I should be at the top of C class. I have not come close to making the podium. I don't really care though, I enter races for my personal enjoyment and the excuse to push hard. Having said that I'm going to do an ftp test in about a week and I expect to get a boost that will put me at at least 3.3 w/kg, B class in most races. At that point I will go from getting my ass handed to me to having my ass served with a side of mountain oysters.

Make sure you understand how the categories work. A 3.0 avg over an entire C race will result in you not seeing the front, especially if it's a short race. Your category is calculated by taking an average of your best 3 FTPs in completed races and group rides in the last 90 days.
Your FTP is considered to be 95% of your best 20 minutes in that event, so the FTP that one manually inputs within profile>settings is not considered for categorisation. If you have done less than 3 events in 90 days then the average FTP from those events will be used. If you are new or have been inactive for 90 days then you will be classified after the first event based on your FTP. In cases where you do not have 20 min data, perhaps because the race lasted less than 20 mins or data pulled from Zwift is missing then they will estimate your FTP at the backend using 10 min data for example. Your average w/kg for the duration of the race is also irrelevant. It is based on that best 20 minute duration. In addition to all of this they will give a rider a small over factor before they upgrade.

Because of the 95% thing, you'd be consistently in the 3.3 range and not really at risk of moving up.