Wind & Altitude : Effects On Power To Weight Ratio

[Cozy Beehive]

acoggan said : Then I suggest that you do some reading, perhaps starting with our wind tunnel validation paper and continuing with studies by Kyle and Berto, etc...just saying, of course.

Efficiency has a strong relationship with chain tension, chordal action and front to rear sprocket ratio selection. I have written about these things before. You just simply can't say that the bicycle is outright 97% efficient, it is misleading. It also ties a bit into stiffness of your frame, and type of bike. If you put a telescopic suspension in the front fork and a swivel suspension in the rear, some portion of pedaling energy will be lost in the compression of the springs. Please think before you post. You're a man of science. Any claim must come with disclaimers.

Similarly, huge numbers are reported for human body efficiency these days on this forum, from 23-25%. I would use a more conservative number of 20%, because this is what most studies show.

 

[Cozy Beehive]

I remember seeing it in a trade-rag a few years ago. I think it was summarised in a STAR-CD (they make CFD software that is used in F1, aerospace, and other areas) mag that they put out. I think the simulation showed about a 2% saving for the front rider, vs. riding solo?

And sorry, I've thrown away the copy we had on the work coffee-table.

This was needless, as I had already pointed the source of the study to Dr.Coggan. It was on his blog all this while and he just forgot about it. http://www.cd-adapco.com/press_room/dynamics/25/tourdefrance.html

 

[acoggan]

Efficiency has a strong relationship with chain tension, chordal action and front to rear sprocket ratio selection. I have written about these things before. You just simply can't say that the bicycle is outright 97% efficient, it is misleading.

Nobody did say that. I merely picked a value that, given the situation, is consistent with the published data.

 

[Le breton]

No, I'd simply forgotten about it.



Then I suggest that you do some reading, perhaps starting with our wind tunnel validation paper and continuing with studies by Kyle and Berto, etc...just saying, of course.



If the balance were such that the reduction in VO2max were always more important, then hour records wouldn't be set at altitude, now would they?

More directly, which effect is more important depends upon:

1) the speed of the cyclist (e.g., riding on the level vs. riding uphill); and

2) the extent to which a given individual is impacted by altitude.



Lots out there, but here's one that springs to mind that made measurements at various "altitudes":

http://www.ncbi.nlm.nih.gov/pubmed/11104308

Edit: not sure if that is the right link, so try this one as well:

http://www.ncbi.nlm.nih.gov/pubmed/12840636

Edit2: here's another good one:

http://www.ncbi.nlm.nih.gov/pubmed/17882451

Since nobody yet pointed it out, I would like you readers to notice that the light green curve (In cozy beehive's plot) does NOT represent the variation in power vs altitude proposed by Basset et al. It shows a drop of more that 20% at 2100m (Tourmalet -> 2115m) against 13.5% proposed by Basset.

 

[Le breton]

Dr. Coggan, the return service was already done by a reader on your blog on July 2. See http://www.trainingandracingwithapowermeter.com/2010/04/does-drafting-benefit-leading-rider_23.html . So lets see, a) you simply skim over the titles of some posts here on the forum and then subtly insult their importance b) you don't read the comments from your own blog readers.

Btw, with regard to that blog post - I have not seen anything as high as 97% efficiency in a bicycle drivetrain so you're slightly overestimating our beautiful machine. Just saying.

Yes I got all the papers you sent me so a big thank you.

By the way, I have to show you this plot :

It shows two phenomena happening as a cyclist exercises at altitude, upto 2200 m (the peak of the Tourmalet).

1) The power relief calculated for a 65 kg rider due to air density decrease - an advantage since drag is reduced. Hence, hour records are broken at altitude. This represented with red line.

I don't know how to reproduce your graph here.
I already pointed out that the green curve does not represents Basset's proposed variation of VO2 with altitude.

NOW FOR THE RED CURVE?
What does it represent? From what you wrote it should be the reduction of drag with altitude (air pressure at constant temperature) for a given object - a cyclist for example.

As I write this I realize that your green curve actually represents the drop in air pressure with altitude!!!

Of course the power needed to overcome the air resistance at a given speed will vary as air density, therefore as the residual air pressure at altitude shown by your green curve.

Since your light green curve represents what your red curve purports to show us, what does that red curve actually mean?

 

[Cozy Beehive]

Since nobody yet pointed it out, I would like you readers to notice that the light green curve (In cozy beehive's plot) does NOT represent the variation in power vs altitude proposed by Basset et al. It shows a drop of more that 20% at 2100m (Tourmalet -> 2115m) against 13.5% proposed by Basset.

Some things you're probably doing wrong.

1) The green curve represents aerobic power drop with altitude for acclimitized runners , hence it was produced using the fit curve Bassett came out with (R^2 = 97%) http://www.midweekclub.ca/powerFAQ.htm#Q17

2) The graph I produced shows that if 100 is sea level power, at 2100 m (~6900 feet) it is 92% of sea level power. If you know how to read a graph, 5 graduations between 80 and 100 means 20/5 = 4. Hence at 2100m, the curve is at 92%, which corresponds to Bassett's table.

3) If power at 2100 m is 92% of sea level value, the drop is 8%, not 13.5, neither is it 20%.

 

[Cozy Beehive]

I don't know how to reproduce your graph here.
I already pointed out that the green curve does not represents Basset's proposed variation of VO2 with altitude.

NOW FOR THE RED CURVE?
What does it represent? From what you wrote it should be the reduction of drag with altitude (air pressure at constant temperature) for a given object - a cyclist for example.

As I write this I realize that your green curve actually represents the drop in air pressure with altitude!!!

Of course the power needed to overcome the air resistance at a given speed will vary as air density, therefore as the residual air pressure at altitude shown by your green curve.

Since your light green curve represents what your red curve purports to show us, what does that red curve actually mean?

Sorry, but isn't the graph given a title and its axes labeled? What do you not understand?

The green curve does not represent a drop of air pressure with altitude. Again, please see my previous reply to you and also http://cozybeehive.blogspot.com/2010/07/wind-altitude-their-effect-on-uphill.html for interpretations.

 

[Le breton]

Some things you're probably doing wrong.

. If you know how to read a graph, 5 graduations between 80 and 100 means 20/5 = 4. .

Yes Cozy, I completed elementary school

 

[Le breton]

Sorry, but isn't the graph given a title and its axes labeled? What do you not understand?
.

Your English obviously, words don't have the same meaning for you and for me. But don't worry, I once had the same type of problem - although of a more subtle nature - with J.D. Jackson's Classical electrodynamics when I first arrived in the States, so you are in good company