Wind & Altitude : Effects On Power To Weight Ratio

[Cozy Beehive]

A curiously rare topic in climbing is what effect the wind has on power to weight ratio. What are your thoughts? How much of an effect?

Here's three different posts by a few that I know aimed to spread lots of insight for those of you interested.

1. Wind & Altitude : Effects on Uphill Cycling by me
2. Effect of wind and bike speed fluctuations on climbing power by Dan Connelly : Part 1, Part 2, Part 3, Part 4
3. Ascension Rates and Power to Body Mass Ratios by Alex Simmons

Curious to know what Andy Coggan, Lim, Ross (Science of Sport) etc think on this topic? What would really interest me is finding out if someone has done a study on the degradation in climbing performance due to shortage of oxygen at high altitude.

 

[Rip:30]

Wind has no effect on either power or weight. Wind effects drag (+/-), and therefore potentially speed.

 

[brianf7]

Power is measured by how you move the total mass forward against whatever force either wind or gradient. whatever you are dragging up hill or whatever you are pushing into the wind.

My Powertap handbook tells me to loose waight to improve but at 185cm that is not possible so I put the powertap on a lighter bike and my power output improved .
I am suposed to change calebration with the lighter bike I need the total waight of bike and rider.

 

[Cozy Beehive]

Wind has no effect on either power or weight. Wind effects drag (+/-), and therefore potentially speed.

I take it that you're joking. You must be the fastest guy in your town then.

 

[forty four]

i often wonder this myself as we all know light riders in wind become useless. even in races with better climbers with me on a climb if there is a strong headwind it seems to remove there advantage over me maybe something to do with momentum and total power. these same guys on flats are not hard to get away from. on flats headwinds remind me of climbing similar efforts but different body types benefit.

 

[acoggan]

A curiously rare topic in climbing is what effect the wind has on power to weight ratio. What are your thoughts? How much of an effect?

Here's three different posts by a few that I know aimed to spread lots of insight for those of you interested.

1. Wind & Altitude : Effects on Uphill Cycling by me
2. Effect of wind and bike speed fluctuations on climbing power by Dan Connelly : Part 1, Part 2, Part 3, Part 4
3. Ascension Rates and Power to Body Mass Ratios by Alex Simmons

Curious to know what Andy Coggan, Lim, Ross (Science of Sport) etc think on this topic?

What do I think? I think Alex's calculations are absolutely trustworthy...the physics are quite well-established, and the guy knows his math. IOW, with respect to the effects of wind there's nothing here to debate (except perhaps just how strong the wind is/was at a particular point on a particular climb on a particular day).

What would really interest me is finding out if someone has done a study on the degradation in climbing performance due to shortage of oxygen at high altitude.

The effects of altitude on aerobic power are also quite well-known. What is also known, however, it that there is significant variation between individuals in the magnitude of any effect, even if you control for the degree of acclimatization.

 

[Rip:30]

I take it that you're joking. You must be the fastest guy in your town then.

Not joking at all. You need to look up the definitions of power and weight.

 

[Rip:30]

Power is measured by how you move the total mass forward against whatever force either wind or gradient. whatever you are dragging up hill or whatever you are pushing into the wind.

My Powertap handbook tells me to loose waight to improve but at 185cm that is not possible so I put the powertap on a lighter bike and my power output improved .
I am suposed to change calebration with the lighter bike I need the total waight of bike and rider.

This is not the definition of power. Your power will stay the same regardless of the bike weight, if you are pedaling with the same torque and angular momentum. Your velocity will increase if you have a lighter set up or less headwind for a given power.

 

[Rip:30]

The effects of altitude on aerobic power are also quite well-known. What is also known, however, it that there is significant variation between individuals in the magnitude of any effect, even if you control for the degree of acclimatization.

Thoughts on the physiology behind attenuated (or exaggerated) loss of aerobic power at altitude for some individuals?

 

[Cozy Beehive]

Not joking at all. You need to look up the definitions of power and weight.

Where did you attend school?

Wind absolutely affects power because it works against forward movement, particularly if its a headwind. If power changes, so does power to weight ratio.

Not going to argue with you, however. Thanks for your time.

 

[Cozy Beehive]

What do I think? I think Alex's calculations are absolutely trustworthy...the physics are quite well-established, and the guy knows his math.

The effects of altitude on aerobic power are also quite well-known. What is also known, however, it that there is significant variation between individuals in the magnitude of any effect, even if you control for the degree of acclimatization.

Thank you!

Whether its Alex, or the other authors in that list, there is lot of uncertainty. We all have done approximations. Frontal area never remains constant, nor does speed or grade or rolling resistance. Its a highly non-linear simulation. My calculations for additional power to weight ratio needed with wind closely match Alex's results though but the approach I have taken is a bit different.

I know the effects of altitude maybe well known, but I havent seen much quantitiative analysis on it. I wouldn't call it "well known". My readers and me are particularly interested in a study on how oxygen concentration affects power delivery, and hence power to weight. You have a link to a study/studies?

 

[acoggan]

Thoughts on the physiology behind attenuated (or exaggerated) loss of aerobic power at altitude for some individuals?

The jury is really still out on that question. However, it could be related to either genetic or possibly early-life-influenced lung structure/function, which impacts the extent to which an individual can maintain SaO2 at altitude (or even at sea level, if the peripheral demand for O2 is high enough).

 

[acoggan]

Whether its Alex, or the other authors in that list, there is lot of uncertainty. We all have done approximations. Frontal area never remains constant, nor does speed or grade or rolling resistance. Its a highly non-linear simulation. My calculations for additional power to weight ratio needed with wind closely match Alex's results though but the approach I have taken is a bit different.

The only uncertainties lie in what to assume for the input variables - once those are fixed, however, the effects of wind are not uncertain at all. (Or are you not really thinking about wind/wind alone??)

I know the effects of altitude maybe well known, but I havent seen much quantitiative analysis on it. I wouldn't call it "well known". My readers and me are particularly interested in a study on how oxygen concentration affects power delivery, and hence power to weight. You have a link to a study/studies?

This is textbook knowledge, really, with perhaps the best/most relevant source being Randy Wilber's excellent book:

http://www.humankinetics.com/products/all-products/altitude-training-and-athletic-performance

Assuming you're not that interested in the question, though, you can find two equations for predicting the average decline in aerobic power as a function of altitude here:

http://www.midweekclub.ca/powerFAQ.htm#Q17

That is the average response, however, and significant variation exists between individuals with respect to the effects of hypoxia on exercise physiology/performance (e.g., http://www.ncbi.nlm.nih.gov/pubmed/16195985).

 

[acoggan]

(Or are you not really thinking about wind/wind alone??)

BTW, I should point out that if your focus isn't on the effect of wind per se but on how to estimate the power required to climb, e.g., l'Alpe de Huez, you shouldn't be using the Bassett et al. equation to estimate frontal area. First, it based upon only a handful of subjects, and second, it is for riders in the aero position, not sitting up and/or standing while climbing on a road bike. Better choices would be:

http://www.ncbi.nlm.nih.gov/pubmed/19199206

or

http://www.ncbi.nlm.nih.gov/pubmed/12355191

Of course, such equations only allow you estimate A, while Cd itself can also vary significantly between riders, even if they aren't using aero bars...

 

[Rip:30]

Where did you attend school?

Wind absolutely affects power because it works against forward movement, particularly if its a headwind. If power changes, so does power to weight ratio.

Not going to argue with you, however. Thanks for your time.

That's wind resistance.

You're getting that confused with power. If you tried to maintain the same velocity into a headwind as you did on a calm day you would by definition need more power. That's very different than asking if wind effects power:weight ratios, because it doesn't. That's the whole point in using power to measure cycling performance--it's independent of road grade, wind resistance, temperature, heart rate, ect.

In rotational systems:
Power = torque x angular velocity

 

[Rip:30]

The jury is really still out on that question. However, it could be related to either genetic or possibly early-life-influenced lung structure/function, which impacts the extent to which an individual can maintain SaO2 at altitude (or even at sea level, if the peripheral demand for O2 is high enough).

Hmm. So by structure, are you thinking total alveolar surface area? Could you test this by also measuring forced vital lung capacity and correlating it to aerobic power decay with altitude?

 

[acoggan]

Hmm. So by structure, are you thinking total alveolar surface area? Could you test this by also measuring forced vital lung capacity and correlating it to aerobic power decay with altitude?

Measuring diffusion capacity would probably be more telling.

In any case, it was studies like this one:

http://www.ncbi.nlm.nih.gov/pubmed/19833809

that I had in mind when I made that comment.

(Hmm: upon rereading that abstract, I'm wondering whether swimming - which is the only sport that seems to induce significant adaptations in lung structure/function, and one that my kids are currently involved in - might have a similar effect as altitude.)

 

[Cozy Beehive]

That's wind resistance.

You're getting that confused with power. If you tried to maintain the same velocity into a headwind as you did on a calm day you would by definition need more power. That's very different than asking if wind effects power:weight ratios, because it doesn't. That's the whole point in using power to measure cycling performance--it's independent of road grade, wind resistance, temperature, heart rate, ect.

In rotational systems:
Power = torque x angular velocity

Race car designer, Mech Engg talking here. I don't think I'm confused.

You're right, in rotational terms at the pedal site, Power = torque x angular velocity. For example, I used this to find out how much watts Cancellara was roughly applying during a Paris Roubaix attack. See here.

Power, however, has multiple equations that helps us to understand certain attitubutes' effect on power. So the above is not the equation you will use.

Did you also know that Power = Force x Velocity? That equation is also not helpful to understand wind's effect on power.

For what we're most concerned about in cycling in terms of wind, grade, rolling resistance, acceleration etc, it is going to roughly be :

Cycling Power = W.Vg.sin[arctan(grade/100)] + W.Vg.Crr.cos[arctan(grade/100)] + 1/2p.Cd.A.(V+Vw)^2 + Power for acceleration + Power to overcome drivetrain losses.

Bottomline, we're dealing with a different beast here. Hope I eliminated your confusion.

 

[acoggan]

Race car designer, Mech Engg talking here. I don't think I'm confused.

You're right, in rotational terms at the pedal site, Power = torque x angular velocity. For example, I used this to find out how much watts Cancellara was roughly applying during a Paris Roubaix attack. See here.

An attitube like power, however, has multiple equations that helps us to understand certain attitubutes' effect on power. So the above is not the equation you will use.

Did you also know that Power = Force x Velocity? That equation is also not helpful to understand wind's effect on power.

For what we're most concerned about in cycling in terms of wind, grade, rolling resistance, acceleration etc, it is going to roughly be :

Cycling Power = W.Vg.sin[arctan(grade/100)] + W.Vg.Crr.cos[arctan(grade/100)] + 1/2p.Cd.A.(V+Vw)^2 + Power for acceleration + Power to overcome drivetrain losses.

Bottomline, we're dealing with a different beast here. Hope I eliminated your confusion.

The confusion seems to be that you are assuming constant speed, whereas Rip:30 is assuming constant power. If speed is indeed constant (as you seem to assume), then yes, wind affects the power demand, but if the power supply is constant (as Rip:30 is assuming), then it only changes the speed.

EDIT: BTW, you're missing a V in the third term of your equation above. It should read 1/2pCdA(V+Vw)^2V.

 

[Cozy Beehive]

EDIT: BTW, you're missing a V in the third term of your equation above. It should read 1/2pCdA(V+Vw)^2V.

Yes, Vg is missed out. Sorry, did it quickly from the work computer.

If power supply is constant, speed or force delivery to the pedals changes or both. Alex Simmons has assumed an even application of power in his analysis which never happens. The main math of the physics of cycling isn't invented by him, it came off a paper from the Journal of Applied Biomechanics.

Let me read the links you have attached before.

 

[Cozy Beehive]

The confusion seems to be that you are assuming constant speed, whereas Rip:30 is assuming constant power. If speed is indeed constant (as you seem to assume), then yes, wind affects the power demand, but if the power supply is constant (as Rip:30 is assuming), then it only changes the speed.

I don't think this has anything to do with what you're saying. The fundamental physics model of cycling is the one I described in the previous post. You can use it to calculate both power, given constant speed, or solve for speed, given constant power. Either way, you will use that equation if you are to know how wind, grade, rolling resistance etc affects power or speed.

 

[Rip:30]

Yes, Vg is missed out. Sorry, did it quickly from the work computer.

If power supply is constant, speed or force delivery to the pedals changes or both. Alex Simmons has assumed an even application of power in his analysis which never happens. The main math of the physics of cycling isn't invented by him, it came off a paper from the Journal of Applied Biomechanics.

Let me read the links you have attached before.

Power will be the same for a max effort TT/climb if it's windy or calm. What changes is wind resistance and thus velocity. Your max power for a given duration has nothing to do with wind. (Who goes less than max in a race, or at least the part of a race where you are interested in power:weight?)

 

[acoggan]

I don't think this has anything to do with what you're saying. The fundamental physics model of cycling is the one I described in the previous post. You can use it to calculate both power, given constant speed, or solve for speed, given constant power. Either way, you will use that equation if you are to know how wind, grade, rolling resistance etc affects power or speed.

Right - but if power supply is assumed to be constant, then as Rip:30 stated wind has absolutely no affect upon it, only upon the resultant speed.

 

[Rip:30]

I don't think this has anything to do with what you're saying. The fundamental physics model of cycling is the one I described in the previous post. You can use it to calculate both power, given constant speed, or solve for speed, given constant power. Either way, you will use that equation if you are to know how wind, grade, rolling resistance etc affects power or speed.

You can use it to estimate power.

 

[acoggan]

The main math of the physics of cycling isn't invented by him, it came off a paper from the Journal of Applied Biomechanics.

No kidding...really? (Heck, he not only uses our model, he uses my slide to describe it...with my complete approval, of course).

BTW, our paper in JAB was far from the first to present a mathematical model of the power requirements of cycling...for example, I remember reading this paper back when I was still an undergraduate student:

http://www.ncbi.nlm.nih.gov/pubmed/468661

However, our paper was the first to actually validate this sort of modeling approach.