# Watt/Kg useless measurement?



## Doc_D

I've been doing some reading lately (Training and Racing with a Power Meter). I'm not sold on using Watt/Kg as a measuring stick.

Over flat ground there is only a very small penalty for being heavier, but there is a huge potential to make more power being a larger person. 

Let's say we have two riders who both an FTP of 4 Watts/Kg. One of the riders is 55 Kg and has an FTP of 220W. The other rider is 110 Kg and has a FTP of 440W. Looking strictly at their watt/Kg you would say they were equal. But when I run the numbers through a calculator the larger rider will clearly be much faster over flat ground and effectively equal to the lighter rider up hills. 

Over flat ground the smaller rider could only average 20.6 mph. The larger rider could average 25.7 mph. Up a 5% grade the smaller rider would average 11.4 mph and the larger rider 12.9 mph.

Granted these are theoretical numbers from a calculator, but they mimic my experience as well. I've ridden with bigger riders who have similar output in watts/kg but who are much faster because there is basically very little penalty for being larger over flat ground.

So am I just missing something or comparing riders based on their Watts/Kg completely useless without taking their total power output into consideration?


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## Alex_Simmons/RST

Doc_D said:


> So am I just missing something or comparing riders based on their Watts/Kg completely useless without taking their total power output into consideration?


W/kg is not a useless measure at all, but comparing different rider's power (or power to weight ratios) is relatively futile. That's why we have races.

On flat terrain, solo rider performance is primarily dictated by power to aero drag ratio (W/m^2). Aerodynamic drag does not scale linearly with body mass, but increases and a lesser rate typically.

On steeper gradients, W/kg takes over as the primary factor and the equation of motion become much more linear.

However the kg part of the performance equation include the weight of the bike and gear etc. For a 55kg rider, the weight of equipment etc is a much larger penalty relative to the large rider.

A 10kg bike + clothes, shoes, bidons etc adds 18% to the small rider's mass, but only 9% to the larger rider's mass. So in reality they no longer have the same W/kg, hence performance will be different.

Nevertheless, despite all that W/kg is still a pretty good predictor of performance potential.

In terms of the relative level each of the various resistance forces play on different gradients, see below for an indication of how the equation changes:


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## cyclesport45

Yup, I'm that 100 kg guy. And, I can ride pipsqueaks off my wheel on the flats, and sprint like a wild man. As soon as the road points UP, it's all over. See the big guy dropped like a bad prom date. Or something like that.


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## Doc_D

The reason I bring this up is because I've been considering trying my hand at racing this year. There is a well known chart that estimates your category based on your watts/kg at various time intervals. The chart shows that to be a mid-pack cat-5 racer you'd have a 20 minute power of about 2.6 watts/Kg. 

But because I'm a smaller guy, I think I'll get destroyed in cat 5 at 2.6 watts/Kg. That would make my 20 minute power about 147 watts. That's only good for for an average speed of 17.7 MPH. But a 110 Kg guy who makes 2.6 watts/Kg will be averaging 21.85 MPH. 

The consensus in my club is that you better be able to average 20 mph solo to be a mid pack cat 5 racer. At my weight that means I'll need a 3.6 watts/Kg while the 110 Kg rider will only need 2 watts/Kg.

So again, using watts/Kg as a measuring stick for your performance seems completely useless to me. 

It's also somewhat depressing to learn that I'll need to put out 3.6 watts/Kg to be a mid pack cat 5 racer.


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## PMC

Doc_D said:


> The reason I bring this up is because I've been considering trying my hand at racing this year. There is a well known chart that estimates your category based on your watts/kg at various time intervals. The chart shows that to be a mid-pack cat-5 racer you'd have a 20 minute power of about 2.6 watts/Kg.
> 
> But because I'm a smaller guy, I think I'll get destroyed in cat 5 at 2.6 watts/Kg. That would make my 20 minute power about 147 watts. That's only good for for an average speed of 17.7 MPH. But a 110 Kg guy who makes 2.6 watts/Kg will be averaging 21.85 MPH.
> 
> The consensus in my club is that you better be able to average 20 mph solo to be a mid pack cat 5 racer. At my weight that means I'll need a 3.6 watts/Kg while the 110 Kg rider will only need 2 watts/Kg.
> 
> So again, using watts/Kg as a measuring stick for your performance seems completely useless to me.
> 
> It's also somewhat depressing to learn that I'll need to put out 3.6 watts/Kg to be a mid pack cat 5 racer.


You are really overthinking this IMO.
Stop worring about numbers for a cat 5 and just go race. You may be suprised.
I can tell you no matter what cat you race you'll never be putting out xx watts for more than xx seconds, it just doesn't really play out that way. 
Go race, have fun and see what happens. If you get dropped like a stone you just need to spend more time on your bike.


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## Alaska Mike

Pin on a number and race. Find a wide back with a good diesel to draft behind in crits and road races, and experiment with positioning in the pack when you feel strong. CAT 5 is all about gaining experience and learning how to race.


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## Wookiebiker

Doc_D said:


> The consensus in my club is that you better be able to average 20 mph solo to be a mid pack cat 5 racer. At my weight that means I'll need a 3.6 watts/Kg while the 110 Kg rider will only need 2 watts/Kg.
> 
> So again, using watts/Kg as a measuring stick for your performance seems completely useless to me.
> 
> It's also somewhat depressing to learn that I'll need to put out 3.6 watts/Kg to be a mid pack cat 5 racer.


I agree with PMC in that you are way over-thinking this.

The power charts you are looking at tell me I have the FTP of a good CAT 3 to an average CAT 2 racer, but the sprint power of a mid level CAT 4...Yet, I hold my own and win enough races against CAT 1/2/3 guys in sprints (I'm one of those 100kg guys).

Racing is different than riding solo in that you can sit in a draft all day...then spend 10 seconds of hard effort in the sprint and win or get a high placing. Tactics are so much more important than anything else when it comes to racing (to a point, since you do need a certain level of fitness to stay in the pack).

I rarely average 20 mph on my solo training rides (though I do a lot of hill work) even on my flatter rides. Yet I have no problem staying in CAT 3 races and am very competitive in Masters (40+) 1/2/3 races.

In the end...pin a number on...go race...and see how you do. There is no other way to find out how well you will do.

If you get dropped...train harder. Before you know it you won't be getting dropped and will start placing well enough.


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## alexp247365

Racing will show you where your weakness lies. It might be a physical weakness, where training could solve. Or, it could be a tactics weakness, such as knowing where to position yourself at certain points of the race (i.e. the final sprint, the correct side of the peloton during a technical turn, or to avoid the wind.)

Racing by default makes you faster, as you don't typically put those kinds of efforts out in training. You're also not going to get the experience necessary to be a better racer without racing.

Like others have said, pin the number on and go have fun. Take mental notes during the course of the event.. and you'll find yourself not only getting faster, but becoming more savvy with how you can navigate through the pack while spending as little energy as possible.


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## kbiker3111

Doc_D said:


> The reason I bring this up is because I've been considering trying my hand at racing this year. There is a well known chart that estimates your category based on your watts/kg at various time intervals. The chart shows that to be a mid-pack cat-5 racer you'd have a 20 minute power of about 2.6 watts/Kg.
> 
> But because I'm a smaller guy, I think I'll get destroyed in cat 5 at 2.6 watts/Kg. That would make my 20 minute power about 147 watts. That's only good for for an average speed of 17.7 MPH. But a 110 Kg guy who makes 2.6 watts/Kg will be averaging 21.85 MPH.
> 
> The consensus in my club is that you better be able to average 20 mph solo to be a mid pack cat 5 racer. At my weight that means I'll need a 3.6 watts/Kg while the 110 Kg rider will only need 2 watts/Kg.
> 
> So again, using watts/Kg as a measuring stick for your performance seems completely useless to me.
> 
> It's also somewhat depressing to learn that I'll need to put out 3.6 watts/Kg to be a mid pack cat 5 racer.


Do you have a powermeter or are all these numbers hypothetical?

There are a few things you are missing about W/kg. First, as Alex said CdA scales with weight. Second, 220W FTP should be relatively easy for a 55 kg rider to produce while 440W FTP would be elite at almost any weight. You're more likely to have a high w/kg if you're a lightweight guy(skinny guys climb well). You're also forgetting that the two deciding moments of a race, accelerations and climbing, have to do with weight. If someone can produce more absolute power than you on flat, steady efforts, let them do it. 

Finally, the most important thing is to disregard those category labels on the Coggan/Allen chart. They are almost meaningless. The chart is only useful as an indicator of strengths and weaknesses and does almost nothing to predict what category you'll be in. I don't know why they don't remove the categories and label everything "good/better/best".


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## overgeared

the posts above make some very good points including 1) that in a road race situation it wont be your 20 minute power that lets you down, more like 1 minute power, simply because races ebb and flow, when people get dropped it's not after 20 mins of sustained pace but brief surge 2) as a smaller rider you will, if you ride smart, benefit really well from the draft of other riders who are on average taller and wider. just give it a go and report back on your power numbers from the race, you may be suprised at the power you need.


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## cyclesport45

Wookiebiker said:


> I agree with PMC in that you are way over-thinking this.
> Racing is different than riding solo in that you can sit in a draft all day...then spend 10 seconds of hard effort in the sprint and win or get a high placing. Tactics are so much more important than anything else when it comes to racing (to a point, since you do need a certain level of fitness to stay in the pack).


Bingo. :thumbsup:


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## chase196126

Doc_D said:


> T
> 
> So again, using watts/Kg as a measuring stick for your performance seems completely useless to me.


Watts/Kg is a good way of comparing ability levels of riders who are different weights, but it is not the end all be all measurement. There are some guys who may produce lower Watts/Kg but are able to get extremely aerodynamic on a Time Trial bike. Zabriskie is a pretty decent example of this. Raw watts on the flats are much less comparable rider to rider than Watts/kilo because of the effect of aerodynamics. 

In general mid sized riders do the best as all around riders because they are heavy large enough to produce a good amount of power to time trial and ride the flats, but are light enough to still climb well. Pure climbers are generally quite small and have very large Watt/kg but not a lot of raw Watts, which makes them effective in the hills but not so much on the flats. Big guys generally thrive on the flats/sprints for the opposite reason. 

Measuring power is an excellent way to train and compare riders but, as others have already said, having good power numbers does not mean you can win a race. Fatigue resistance and being able to produce good numbers over and over is going to make you a better racer than being able to put out excellent numbers only once in a race.


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## Doc_D

Thanks for the advice everyone. I do plan to try my hand at racing this spring. I have done some practice races with my club over the last couple of years which is why I know that I get hurt pretty badly buy larger guys with a similar watt/Kg output as myself.

My point of this discussion really wasn't to bring up my concerns about going racing. It was simply to point out that many coaches and experts seem to use watts/kg as a measure of performance that is independant of anything else. But in my experience that is absolutely not true. A 110Kg rider that has a FTP of 3 watts/Kg (330 watt FTP) would be quite strong/fast rider while a 55 Kg rider that has a FTP of 3 watts/Kg (165 watt FTP) would not be a very strong/fast rider. 

So I'm just confused why watts/Kg is thrown around as the gold standard of measuring someone's performance when really it's seems like a pretty poor measure.


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## new2rd

probably because it's assuming that the cylist is a typical professional rider 60-70 kg depending on height, so it's just a comparison. Don't worry about all this non-sense. I'm planning on racing for my first time in March. I plan on being strong enough to stay in a group, hide and conserve as much energy as possible, and hopefully I feel pretty good towards the end. I'm keeping it simple. I'll work hard if needed to stay in the draft, but my main goal is to conserve as much as possible for the end.


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## Alex_Simmons/RST

Doc_D said:


> So I'm just confused why watts/Kg is thrown around as the gold standard of measuring someone's performance when really it's seems like a pretty poor measure.


Because the point is to compare yourself to yourself, not to others.

If your W/kg increases, then your performance will as well. As a coach I look at the watts and W/kg over key durations of interest (amongst other things), so I can track what type of rider I am working with and what improvements we need to make, as well as what improvements are being made.

The whole point of the power profile chart is to assess your individual strengths and weaknesses, not to assess what race category you can ride in. The author of the chart (Dr Coggan) makes this very clear in his accompanying text, and indeed he was not particularly enamored with the idea of putting race categories on there at all, but he received vociferous opposition when those labels were removed, that they made their way back.

Now of course a cat 3 in one region may not be as strong as a cat 3 field as in another, so they are only guidelines. 

In general though what you can say is that if you have an FTP W/kg that's at the upper range in a category, and are still getting dropped, then fitness is most likely not the problem, but rather other factors that go into making a good bike racer.

Like I said, we have bike races to determine race outcomes and gradings. Plenty of "weaker" riders win bike races because they are smarter, craftier, experienced and skillful.

Go race and have some fun.


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## kbiker3111

Doc_D said:


> Thanks for the advice everyone. I do plan to try my hand at racing this spring. I have done some practice races with my club over the last couple of years which is why I know that I get hurt pretty badly buy larger guys with a similar watt/Kg output as myself.
> 
> My point of this discussion really wasn't to bring up my concerns about going racing. It was simply to point out that many coaches and experts seem to use watts/kg as a measure of performance that is independant of anything else. But in my experience that is absolutely not true. A 110Kg rider that has a FTP of 3 watts/Kg (330 watt FTP) would be quite strong/fast rider while a 55 Kg rider that has a FTP of 3 watts/Kg (165 watt FTP) would not be a very strong/fast rider.
> 
> So I'm just confused why watts/Kg is thrown around as the gold standard of measuring someone's performance when really it's seems like a pretty poor measure.


Again, 330 is relatively average FTP for a well trained amateur racer. 165 watts is really low for a young male cyclist, to the point of being untrained. The point you are missing is the *KG* part of w/kg. Lower your kg and your w/kg goes up! Certainly, any cyclist at 110kg could lose a good 20 kg unless they are exceedingly tall. Losing 20 kg while maintaining a ftp of 330 would bring the w/kg from a low 3.0 to a much better 3.67. Its basically what Wiggins did.


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## Doc_D

Alex_Simmons/RST said:


> Because the point is to compare yourself to yourself, not to others.


Thanks Alex, I think I've finally got it through my thick skull. That makes sense. I've been dropping weight all winter so comparing myself to myself with watts/Kg instead of just watts would make sense.

I think I was confused because people are misusing watts/Kg to compare themselves to others which, unless they are relatively close in weight, doesn't seem applicable.


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## Nevermiss

I'm entering my first road race in 3 weeks and I've just decided to go for it. I'm another one of those 100 kg guys. I've got a 1600 watt sprint but only 3.15 watts/kg FTP. I think its appropriate that guys like me are called superclydes, since I will really function as a draft horse until we hit the big hills and then all the skinny guys will pass me like I'm Grandma Kettle on the Autobahn. FEAR ME ON THE DESCENT!

Can't wait to try track racing!


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## Ghost234

Don't get too hung up on the numbers. Cat 4/5 is often a mix of everything under the sun. I've seen people racing cat 4 that have never ridden more than 50km and others who are able to TT like the pro/1/2. 

I'm race cat 3, and for most of my racing career I've always been way above my category of racing according to the chart. The chart puts my FTP into mid cat 1, but yet I don't feel that I am remotely close enough to be racing at that level yet. I don't consider myself a climber in the least despite my weight (65kg) but rather I always seem to get my best results TT'ing - so don't consider yourself restricted in the least.


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## Alex_Simmons/RST

Doc_D said:


> Thanks Alex, I think I've finally got it through my thick skull.


Not too thick I hope, it'll lower your power to weight ratio


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## stevesbike

Alex_Simmons/RST said:


> Because the point is to compare yourself to yourself, not to others.
> 
> If your W/kg increases, then your performance will as well. As a coach I look at the watts and W/kg over key durations of interest (amongst other things), so I can track what type of rider I am working with and what improvements we need to make, as well as what improvements are being made.
> 
> .


That seems like an over-generalization. Wiggins, for example, increased his watts/kg, which improved his climbing, but reduced his pursuit performance since it decreased his overall power. I think there's often too much extrapolation of protour rider goals to amateur racing. Watts/kg matters a lot if your racing involves climbs, but a lot of US racing, for example, does not. And if increasing watts/kg comes at the expense of absolute power, the tradeoff may not be worth it - even true for someone like Cancellara who may be able to produce 480 watts at threshold, which translates only into a 'mediocre' 5.8 watts/kg.


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## Alex_Simmons/RST

stevesbike said:


> That seems like an over-generalization. Wiggins, for example, increased his watts/kg, which improved his climbing, but reduced his pursuit performance since it decreased his overall power. I think there's often too much extrapolation of protour rider goals to amateur racing. Watts/kg matters a lot if your racing involves climbs, but a lot of US racing, for example, does not. And if increasing watts/kg comes at the expense of absolute power, the tradeoff may not be worth it - even true for someone like Cancellara who may be able to produce 480 watts at threshold, which translates only into a 'mediocre' 5.8 watts/kg.


It's still a pretty solid generalisation when considering the same type of event/racing. Not many I know improve their W/kg over durations of interest (even in flat events like TT) and perform more poorly.

I'm well aware of the demands of totally different events, hence my comment about inspecting W/kg for durations of interest and the detail in post #2 in this thread regarding the balance between aerodynamics, power and mass depending on the nature of event and terrain.


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## new2rd

Alex_Simmons/RST said:


> It's still a pretty solid generalisation when considering the same type of event/racing. Not many I know improve their W/kg over durations of interest (even in flat events like TT) and perform more poorly.
> 
> I'm well aware of the demands of totally different events, hence my comment about inspecting W/kg for durations of interest and the detail in post #2 in this thread regarding the balance between aerodynamics, power and mass depending on the nature of event and terrain.


I'm a newbie to racing and I believe in keeping it simple, but what is a "duration of interest" when it come to a 2 1/2-3 hr road race?


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## stevesbike

Alex_Simmons/RST said:


> It's still a pretty solid generalisation when considering the same type of event/racing. Not many I know improve their W/kg over durations of interest (even in flat events like TT) and perform more poorly.
> 
> I'm well aware of the demands of totally different events, hence my comment about inspecting W/kg for durations of interest and the detail in post #2 in this thread regarding the balance between aerodynamics, power and mass depending on the nature of event and terrain.


but the reason is typically because they have simply increased their wattage (and held their weight fairly constant). While it's true that the ratio has increased, so too has their watt/height ratio, but obviously we don't think there's anything magical about that. The role of the weight term in the ratio becomes important mainly in climbing, but even still a rider who is already fit only gains an increased advantage in losing weight if 1) they hold their wattage at least non-decreasing while losing weight, and 2) if their races involve a lot of climbing. A rider who loses 2kg will only save about 3 seconds on a 5% climb/km. Obviously if one is climbing 200+ km stages with 70 km of climbs, then this is a lot. Not so much if your race is the tour de parc industriale...


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## bytewalls

*Watts/kg can mean little to nothing*



Doc_D said:


> The reason I bring this up is because I've been considering trying my hand at racing this year. There is a well known chart that estimates your category based on your watts/kg at various time intervals. The chart shows that to be a mid-pack cat-5 racer you'd have a 20 minute power of about 2.6 watts/Kg.
> 
> But because I'm a smaller guy, I think I'll get destroyed in cat 5 at 2.6 watts/Kg. That would make my 20 minute power about 147 watts. That's only good for for an average speed of 17.7 MPH. But a 110 Kg guy who makes 2.6 watts/Kg will be averaging 21.85 MPH.
> 
> The consensus in my club is that you better be able to average 20 mph solo to be a mid pack cat 5 racer. At my weight that means I'll need a 3.6 watts/Kg while the 110 Kg rider will only need 2 watts/Kg.
> 
> So again, using watts/Kg as a measuring stick for your performance seems completely useless to me.
> 
> It's also somewhat depressing to learn that I'll need to put out 3.6 watts/Kg to be a mid pack cat 5 racer.


I come in at 52kg, solo ride at 17-18mph, average maybe 17 on my long rides and race as a cat 3. In 123 crits I can usually pull out a top 10. Get out and race your power numbers will improve. Learn how to get low and aero and find a good wheel. Learn how to take advantage of your advantages as a smaller ride (acceleration and climbing). Then minimize your disadvantage by sitting in the group when it applies. I have had races with avg power of 100watts, but average speeds of 26-28mph because small people get a really good draft. Most of all have fun


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