The zero wind tunnel option for serious cyclists

Andre Jute said:

with a very high degree of accuracy.

Hmmm. I suppose that depends on how one interprets "very high."

Andre Jute said:

Yo, Joseph, as I promised, I have published an article showing how a
cyclist can discover his power output and Cd with no tools except his
bike and a road, yet with a very high degree of accuracy. Seehttp://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycl...

HTH.

Andre Jute
 http://members.lycos.co.uk/fiultra/BICYCLE%20%26%20CYCLING.html

Cyclist power is highly irregular. Chis Hoy powering to a world record
standing start kilometer puts out way more power than he could out
training on some long hill climb. He probably doesn't care what his
sustainable aerobic power is, likewise Leonardo Piepoli probably
doesn't care what his stanidng start power is. Muscle strength,
gearing, and a whole bunch of other factors make an acceleration test
for cyclists problematic.

Perhaps a more suitable way would be to use a hill of known slope and
coast down from a standing start, and measure elapsed time and if
possible speed at the end of the course.

That way you get to use the nice and consistent gravitational force
instead of the variable pedal power.

I have a constant slope hill with a clear 300m or so that would be
good for such a test. I just don't know what to do with the info I
could gather there.

Joseph

<[email hidden]> wrote in message
news:[email hidden]...
[Snip]

Perhaps a more suitable way would be to use a hill of known slope and
coast down from a standing start, and measure elapsed time and if
possible speed at the end of the course.

That way you get to use the nice and consistent gravitational force
instead of the variable pedal power.

I have a constant slope hill with a clear 300m or so that would be
good for such a test. I just don't know what to do with the info I
could gather there.

Hi Joseph,

If you really want to try this and accept the inaccuracies in your knowledge
of the slope and other inputs then I would recommend you try using the
formula below. All it does is balance the forces between those of gravity
and both wind and rolling resistance to estimate your CdA. In order to get
the best approximation you need to reach terminal velocity on the run down
the slope, i.e. you reach your maximum steady speed. The best way to do this
is to do several runs whereby your pedal up to as close to the maximum speed
you reached on your previous run before hitting the slope as this will give
you the best chance at achieving a steady terminal velocity.

CdA = (9.8 x kg x (gradient - Crr)) / (0.5 x air density x speed squared)

where:
kg is the weigth in kilogrammes of you and your bike
gradient is the fractional gradient of the slope
Crr is rolling resistance plus if you like a very small addition for hub
bearing resistance
speed is in m/s (sorry about the SI units)

To take an example from a local hill where I tried this on the drops

kg = 90 gradient = 0.1(10%) speed = 21m/s(47mph) air density = 1.23kg/m
cubed.

CdA = (9.8 x 90 x (0.1-0.006)) / (0.5 x 1.23 x 21 x 21)

CdA = 0.31

Whilst the result looks to be in the right ball park it all hinges on how
accurate the 10% figure is for the gradient of the hill. I took an average
from a digital map. Have fun and let us know your results.

Graham.

graham said:

<[email hidden]> wrote in message

news:[email hidden]...
[Snip]

Perhaps a more suitable way would be to use a hill of known slope and
coast down from a standing start, and measure elapsed time and if
possible speed at the end of the course.

That way you get to use the nice and consistent gravitational force
instead of the variable pedal power.

I have a constant slope hill with a clear 300m or so that would be
good for such a test. I just don't know what to do with the info I
could gather there.

Hi Joseph,

If you really want to try this and accept the inaccuracies in your knowledge
of the slope and other inputs then I would recommend you try using the
formula below. All it does is balance the forces between those of gravity
and both wind and rolling resistance to estimate your CdA. In order to get
the best approximation you need to reach terminal velocity on the run down
the slope, i.e. you reach your maximum steady speed. The best way to do this
is to do several runs whereby your pedal up to as close to the maximum speed
you reached on your previous run before hitting the slope as this will give
you the best chance at achieving a steady terminal velocity.

CdA = (9.8 x kg x (gradient - Crr)) / (0.5 x air density x speed squared)

where:
kg is the weigth in kilogrammes of you and your bike
gradient is the fractional gradient of the slope
Crr is rolling resistance plus if you like a very small addition for hub
bearing resistance
speed is in m/s (sorry about the SI units)

To take an example from a local hill where I tried this on the drops

kg = 90 gradient = 0.1(10%)   speed = 21m/s(47mph) air density =1.23kg/m
cubed.

CdA = (9.8 x 90 x (0.1-0.006)) / (0.5 x 1.23 x 21 x 21)

CdA = 0.31

Whilst the result looks to be in the right ball park it all hinges on how
accurate the 10% figure is for the gradient of the hill. I took an average
from a digital map. Have fun and let us know your results.

Graham.

That is perfect. I am unfortunately grounded for the weekend, so I
won't be able to test until later next week.

What type of gradient? Is that distance travelled over rise?

Joseph

<[email hidden]> wrote in message
news:[email hidden]...

graham said:

<[email hidden]> wrote in message

news:[email hidden]...
[Snip]
If you really want to try this and accept the inaccuracies in your
knowledge
of the slope and other inputs then I would recommend you try using the
formula below. All it does is balance the forces between those of gravity
and both wind and rolling resistance to estimate your CdA. In order to get
the best approximation you need to reach terminal velocity on the run down
the slope, i.e. you reach your maximum steady speed. The best way to do
this
is to do several runs whereby your pedal up to as close to the maximum
speed
you reached on your previous run before hitting the slope as this will
give
you the best chance at achieving a steady terminal velocity.

CdA = (9.8 x kg x (gradient - Crr)) / (0.5 x air density x speed squared)

where:
kg is the weigth in kilogrammes of you and your bike
gradient is the fractional gradient of the slope
Crr is rolling resistance plus if you like a very small addition for hub
bearing resistance
speed is in m/s (sorry about the SI units)

To take an example from a local hill where I tried this on the drops

kg = 90 gradient = 0.1(10%) speed = 21m/s(47mph) air density = 1.23kg/m
cubed.

CdA = (9.8 x 90 x (0.1-0.006)) / (0.5 x 1.23 x 21 x 21)

CdA = 0.31

Whilst the result looks to be in the right ball park it all hinges on how
accurate the 10% figure is for the gradient of the hill. I took an average
from a digital map. Have fun and let us know your results.

Graham.

That is perfect. I am unfortunately grounded for the weekend, so I
won't be able to test until later next week.

What type of gradient? Is that distance travelled over rise?

For the above formula you want rise over horizontal distance travelled. For
modest road gradients the error is very small if you use rise over distance
travelled.

Graham.

Andre Jute said:

Yo, Joseph, as I promised, I have published an article showing how a
cyclist can discover his power output and Cd with no tools except his
bike and a road, yet with a very high degree of accuracy.

Use terminal speed on a downhill to get CdA, and a climb to get power.
More accurate and simpler. The power part will always have a time
attached to it (ie 300 watts for 10 minutes).

Quoted message said:

Andre Jute said:

Yo, Joseph, as I promised, I have published an article showing how a
cyclist can discover his power output and Cd with no tools except his
bike and a road, yet with a very high degree of accuracy. See http://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycl...

HTH.

Andre Jute
 http://members.lycos.co.uk/fiultra/BICYCLE%20%26%20CYCLING.html

Cyclist power is highly irregular. Chis Hoy powering to a world record
standing start kilometer puts out way more power than he could out
training on some long hill climb. He probably doesn't care what his
sustainable aerobic power is, likewise Leonardo Piepoli probably
doesn't care what his stanidng start power is. Muscle strength,
gearing, and a whole bunch of other factors make an acceleration test
for cyclists problematic.

The method I'm suggesting is exceedingly subtle, so it takes a while
to understand how it overcomes all these difficulties you raise. My
method uses repeated surplus traction measurements over your speed
range (that's those iterative acceleration readings) to measure very
closely your power *on the day*, and then, without any assumptions or
manufactured constants -- fudge factors, guesses, kludges --
approximates very closely all the other factors lumped together that
influences Cd (that's the coastdown tests) to determine your Cd.

This business of adjusting constants -- fudge factors, guestimates,
street myths, wishful thinking -- is important. Notice for instance
that I made -- it took me two days of hard thought to get there -- a
formula that entirely obviates the necessity for working with the
rolling resistance of some notional tire because I saw too wide a
range in the data you referred me to, and didn't trust the idea of a
lab test with a drum substituting for the road. Instead, I made my
formula include the actual tyres you use on the test, with a real
measurement, not a guesstimate, no matter how distinguished the
guesser. In fact, I made my formula work so that it can operate as a
check on the Cr guess!

But if you think my suggestion is too much work, then that's it;
someone else will take it up sooner or later and then we'll find out
who's right. All I can say is that my method has worked for a quarter-
century for special car builders who bought my book (they write to me
to tell me so) and before that, back into the nineteenth century, for
automobile engineers and before them railway engineers, whose methods
I adapted in the light of modern requirements and knowledge. (It isn't
like I invented anything weird: I just rearranged and reapplied widely
known physics to overcome practical difficulties in cyclist
measurements.)

Quoted message said:

Perhaps a more suitable way would be to use a hill of known slope and
coast down from a standing start, and measure elapsed time and if
possible speed at the end of the course.

Sure, if that's what you want to do. It sounds a lot easier and
quicker than my method, but it only gets you one reading; even
averaging several runs gets you only one data-point (my suggestion
gets you averages on many data points -- you could for instance use
the data gathered for my method to calculate your optimum gearset). To
exclude the other factors from your reading of downhill speed to
arrive at Cd, you must then have instruments not available to you, or
make all kinds of assumptions about conditions and mechanical
reactions. My method, while more tedious, excludes these sources of
error.

Quoted message said:

That way you get to use the nice and consistent gravitational force
instead of the variable pedal power.

The second, coastdown part of my suggested test also uses
gravitational force. The iterative acceleration tests overcomes the
perceived problem of variable pedal power. You keep trying to solve
the problem with one big bang, by measuring top speed and trying to
deduce power from that; that is obviously a very fallible method. My
method argues that you exhibit maximum power on acceleration, and by
repeated tests over various ranges with results averaged, it will give
a more reliable final reading. What's more, my method separates the
distribution of the power between the resistances without making any
assumptions and without any fudge factors.

Quoted message said:

I have a constant slope hill with a clear 300m or so that would be
good for such a test. I just don't know what to do with the info I
could gather there.

Graham has already supplied a formula

We'll find out after you do the downhill test whether the Cd you
calculate predicts your maximum speed pedaling flat out along a flat
road, which is the point of having a Cd number. One thing is for sure:
if you merely want a cafe Cd closer to the 0.3 you dream of than the
c0.5 average (for 80 per cent of racing cyclists, say) that I suspect,
you're more likely to have your wish fulfilled with the downhill
shortcut than my method!

For those who want to look it up, we're referring to my article at:

http://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycling%20parameters.html

Good luck with the test.

Andre Jute
No such thing as a free lunch -- Hayek
Never ate lunch in my life -- Armstrong

Andre Jute said:

The method I'm suggesting is exceedingly subtle, so it takes a while
to understand how it overcomes all these difficulties you raise.

I'm more interested in your claim of "a very high degree of accuracy."
Would you kindly provide an example that shows either the accuracy or
precision of your exceedingly subtle method?

Andre Jute said:

Quoted message said:

Andre Jute said:

Yo, Joseph, as I promised, I have published an article showing how a
cyclist can discover his power output and Cd with no tools except his
bike and a road, yet with a very high degree of accuracy. Seehttp://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycl...

Quoted message said:

Quoted message said:

HTH.

Quoted message said:

Quoted message said:

Andre Jute
 http://members.lycos.co.uk/fiultra/BICYCLE%20%26%20CYCLING.html

Quoted message said:

Cyclist power is highly irregular. Chis Hoy powering to a world record
standing start kilometer puts out way more power than he could out
training on some long hill climb. He probably doesn't care what his
sustainable aerobic power is, likewise Leonardo Piepoli probably
doesn't care what his stanidng start power is. Muscle strength,
gearing, and a whole bunch of other factors make an acceleration test
for cyclists problematic.

The method I'm suggesting is exceedingly subtle, so it takes a while
to understand how it overcomes all these difficulties you raise. My
method uses repeated surplus traction measurements over your speed
range (that's those iterative acceleration readings) to measure very
closely your power *on the day*, and then, without any assumptions or
manufactured constants -- fudge factors, guesses, kludges --
approximates very closely all the other factors lumped together that
influences Cd (that's the coastdown tests) to determine your Cd.

This business of adjusting constants -- fudge factors, guestimates,
street myths, wishful thinking -- is important. Notice for instance
that I made -- it took me two days of hard thought to get there -- a
formula that entirely obviates the necessity for working with the
rolling resistance of some notional tire because I saw too wide a
range in the data you referred me to, and didn't trust the idea of a
lab test with a drum substituting for the road. Instead, I made my
formula include the actual tyres you use on the test, with a real
measurement, not a guesstimate, no matter how distinguished the
guesser. In fact, I made my formula work so that it can operate as a
check on the Cr guess!

But if you think my suggestion is too much work, then that's it;
someone else will take it up sooner or later and then we'll find out
who's right. All I can say is that my method has worked for a quarter-
century for special car builders who bought my book (they write to me
to tell me so) and before that, back into the nineteenth century, for
automobile engineers and before them railway engineers, whose methods
I adapted in the light of modern requirements and knowledge. (It isn't
like I invented anything weird: I just rearranged and reapplied widely
known physics to overcome practical difficulties in cyclist
measurements.)

Quoted message said:

Perhaps a more suitable way would be to use a hill of known slope and
coast down from a standing start, and measure elapsed time and if
possible speed at the end of the course.

Sure, if that's what you want to do. It sounds a lot easier and
quicker than my method, but it only gets you one reading; even
averaging several runs gets you only one data-point (my suggestion
gets you averages on many data points -- you could for instance use
the data gathered for my method to calculate your optimum gearset). To
exclude the other factors from your reading of downhill speed to
arrive at Cd, you must then have instruments not available to you, or
make all kinds of assumptions about conditions and mechanical
reactions. My method, while more tedious, excludes these sources of
error.

Quoted message said:

That way you get to use the nice and consistent gravitational force
instead of the variable pedal power.

The second, coastdown part of my suggested test also uses
gravitational force. The iterative acceleration tests overcomes the
perceived problem of variable pedal power. You keep trying to solve
the problem with one big bang, by measuring top speed and trying to
deduce power from that; that is obviously a very fallible method. My
method argues that you exhibit maximum power on acceleration, and by
repeated tests over various ranges with results averaged, it will give
a more reliable final reading. What's more, my method separates the
distribution of the power between the resistances without making any
assumptions and without any fudge factors.

Quoted message said:

I have a constant slope hill with a clear 300m or so that would be
good for such a test. I just don't know what to do with the info I
could gather there.

Graham has already supplied a formula

We'll find out after you do the downhill test whether the Cd you
calculate predicts your maximum speed pedaling flat out along a flat
road, which is the point of having a Cd number. One thing is for sure:
if you merely want a cafe Cd closer to the 0.3 you dream of than the
c0.5 average (for 80 per cent of racing cyclists, say) that I suspect,
you're more likely to have your wish fulfilled with the downhill
shortcut than my method!

For those who want to look it up, we're referring to my article at:

http://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycl...

Good luck with the test.

Andre Jute
No such thing as a free lunch -- Hayek
Never ate lunch in my life -- Armstrong

I have no doubt your method works, and I expect I will use some parts
to check the Crr values. I think the hill roll down will work well
because it uses a constant force of gravity working on the constant
mass of the rider/bike instead of the variable force avialable form
the rider.

Joseph

In article
<[email hidden]>,

Andre Jute said:

Yo, Joseph, as I promised, I have published an article showing how a
cyclist can discover his power output and Cd with no tools except his
bike and a road, yet with a very high degree of accuracy. See
http://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycling%20par
ameters.html

HTH.

Not so much in terms of "publishing." You've posted a Web page is all;
that's different than publishing in the scientific sense of the word.
There's no peer review of your article, for example. This leads to some
potential confounds. Your assumptions regarding rolling resistance, for
example, are not tenable. You neglect other factors like barometric
pressure, wind speed and direction, road surface quality (retreating to
the unquantifiable "reasonably smooth road"😉, etc. Your only citation
is self-referential to a book you purportedly wrote. Then at the end
you totally defeat your article by saying it doesn't matter much anyway!

It's this fundamental lack of rigor in your thinking including faulty
logic, self-contradictions, etc. that undermine you every time you post
something about bicycles. You're just another Usenet blowhard.

Polymath? Please. You must have read too much John Brunner as a youth.

"Andre Jute" <[email hidden]> wrote in message
news:[email hidden]...
[email hidden] <[email hidden]> wrote:

Graham has already supplied a formula

We'll find out after you do the downhill test whether the Cd you
calculate predicts your maximum speed pedaling flat out along a flat
road, which is the point of having a Cd number. One thing is for sure:
if you merely want a cafe Cd closer to the 0.3 you dream of than the
c0.5 average (for 80 per cent of racing cyclists, say) that I suspect,
you're more likely to have your wish fulfilled with the downhill
shortcut than my method!

Andre,

I have read your article and would not argue with most of it. I do however
find your statement above about wish fulfillment a little harsh. I have
conducted many of these tests in the past and after a good degree of
averaging I arrived at CdA figures as used in the formula I suggested to
Joseph of 0.51 riding with my hands on the hoods, 0.34 on the drops and 0.31
on my race bike on my tri bars (I am a veteran triathlete). Clearly when
doing such tests by far the biggest uncertainty is in determining the slope
of the hill which introduces considerable scatter in the results.

If , however, I plug the 0.31 number into a power calculation for my last
40km TT in 65 mins using the other data I gave in my example to Joseph
together with an overall drive train efficiency of 95% (obviously not needed
in a coast down calc) it has me putting out around 250W which does not seem
too bad for an old timer like me. If however I were to use your figure of
0.5 (assuming you mean the same as what Joseph and I mean by a CdA of 0.3
when you speak of a Cd of 0.5) that would put me closer to 350W for over a
hour which I think would be flattering indeed.

Graham.

email hidden said:

Andre Jute said:

Quoted message said:

On May 10, 12:47 am, Andre Jute <[email hidden]> wrote:
> Yo, Joseph, as I promised, I have published an article showing how a
> cyclist can discover his power output and Cd with no tools except his
> bike and a road, yet with a very high degree of accuracy. Seehttp://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycl...

Quoted message said:

Quoted message said:

> HTH.

Quoted message said:

Quoted message said:

> Andre Jute
>  http://members.lycos.co.uk/fiultra/BICYCLE%20%26%20CYCLING.html

Quoted message said:

Quoted message said:

Cyclist power is highly irregular. Chis Hoy powering to a world record
standing start kilometer puts out way more power than he could out
training on some long hill climb. He probably doesn't care what his
sustainable aerobic power is, likewise Leonardo Piepoli probably
doesn't care what his stanidng start power is. Muscle strength,
gearing, and a whole bunch of other factors make an acceleration test
for cyclists problematic.

Quoted message said:

The method I'm suggesting is exceedingly subtle, so it takes a while
to understand how it overcomes all these difficulties you raise. My
method uses repeated surplus traction measurements over your speed
range (that's those iterative acceleration readings) to measure very
closely your power *on the day*, and then, without any assumptions or
manufactured constants -- fudge factors, guesses, kludges --
approximates very closely all the other factors lumped together that
influences Cd (that's the coastdown tests) to determine your Cd.

Quoted message said:

This business of adjusting constants -- fudge factors, guestimates,
street myths, wishful thinking -- is important. Notice for instance
that I made -- it took me two days of hard thought to get there -- a
formula that entirely obviates the necessity for working with the
rolling resistance of some notional tire because I saw too wide a
range in the data you referred me to, and didn't trust the idea of a
lab test with a drum substituting for the road. Instead, I made my
formula include the actual tyres you use on the test, with a real
measurement, not a guesstimate, no matter how distinguished the
guesser. In fact, I made my formula work so that it can operate as a
check on the Cr guess!

Quoted message said:

But if you think my suggestion is too much work, then that's it;
someone else will take it up sooner or later and then we'll find out
who's right. All I can say is that my method has worked for a quarter-
century for special car builders who bought my book (they write to me
to tell me so) and before that, back into the nineteenth century, for
automobile engineers and before them railway engineers, whose methods
I adapted in the light of modern requirements and knowledge. (It isn't
like I invented anything weird: I just rearranged and reapplied widely
known physics to overcome practical difficulties in cyclist
measurements.)

Quoted message said:

Quoted message said:

Perhaps a more suitable way would be to use a hill of known slope and
coast down from a standing start, and measure elapsed time and if
possible speed at the end of the course.

Quoted message said:

Sure, if that's what you want to do. It sounds a lot easier and
quicker than my method, but it only gets you one reading; even
averaging several runs gets you only one data-point (my suggestion
gets you averages on many data points -- you could for instance use
the data gathered for my method to calculate your optimum gearset). To
exclude the other factors from your reading of downhill speed to
arrive at Cd, you must then have instruments not available to you, or
make all kinds of assumptions about conditions and mechanical
reactions. My method, while more tedious, excludes these sources of
error.

Quoted message said:

Quoted message said:

That way you get to use the nice and consistent gravitational force
instead of the variable pedal power.

Quoted message said:

The second, coastdown part of my suggested test also uses
gravitational force. The iterative acceleration tests overcomes the
perceived problem of variable pedal power. You keep trying to solve
the problem with one big bang, by measuring top speed and trying to
deduce power from that; that is obviously a very fallible method. My
method argues that you exhibit maximum power on acceleration, and by
repeated tests over various ranges with results averaged, it will give
a more reliable final reading. What's more, my method separates the
distribution of the power between the resistances without making any
assumptions and without any fudge factors.

Quoted message said:

Quoted message said:

I have a constant slope hill with a clear 300m or so that would be
good for such a test. I just don't know what to do with the info I
could gather there.

Quoted message said:

Graham has already supplied a formula

Quoted message said:

We'll find out after you do the downhill test whether the Cd you
calculate predicts your maximum speed pedaling flat out along a flat
road, which is the point of having a Cd number. One thing is for sure:
if you merely want a cafe Cd closer to the 0.3 you dream of than the
c0.5 average (for 80 per cent of racing cyclists, say) that I suspect,
you're more likely to have your wish fulfilled with the downhill
shortcut than my method!

Quoted message said:

For those who want to look it up, we're referring to my article at:

Quoted message said:

http://members.lycos.co.uk/fiultra/BICYCLE%20TECH%20--%20basic%20cycl...

Quoted message said:

Good luck with the test.

Quoted message said:

Andre Jute
No such thing as a free lunch -- Hayek
Never ate lunch in my life -- Armstrong

I have no doubt your method works, and I expect I will use some parts
to check the Crr values. I think the hill roll down will work well
because it uses a constant force of gravity working on the constant
mass of the rider/bike instead of the variable force avialable form
the rider.

Joseph

There is also the question of how much precision you need for a
practical result. Graham tells in a concurrent post of impressive
empirical crosschecks on the downhill method. Good luck.

Andre Jute
http://members.lycos.co.uk/fiultra/BICYCLE%20%26%20CYCLING.html

"Andre Jute" <[email hidden]> wrote in message
news:[email hidden]...

email hidden said:

Andre Jute said:

[email hidden] <[email hidden]> wrote:

[Snip]

There is also the question of how much precision you need for a
practical result. Graham tells in a concurrent post of impressive
empirical crosschecks on the downhill method. Good luck.

Andre Jute

Andre,

I am not sure my results are all that impressive merely within the bounds of
what might reasonably be expected. I am sure we all realise the difficulties
of matching theory to reality when it comes to cycling on the open road but
I have found over the years of building a model of "me" both running and
cycling - never got anywhere with swimming!!! - I have managed by a process
of cross comparison and averaging to be able to get some reasonably
consistant results. This goes as far as average heart rates and times for
both cycling and running events or triathlon splits. I fully support your
approach of using a series of different test environments to emperically
derive the important variables but I also recognise there are large
uncertainty bands around any one off result. All my data has been collected
via my Garmin F301 over a period of several years. In an attempt to overcome
the Garmin's large error margin on altitute I have used a digital mapping
package to provide the altitude and hence gradient data for my modelling.

In Joseph's case then the down hill method whilst not delivering "precision"
will allow him to do comparative tests on his position on the bike or
possibly even between his wheel sets providing he does them on the same day
and can follow the same line down the hill. In short all I am saying is that
I agree with your basic premise that provided you understand the basic
physics and you do reasonably controlled tests the law of averages gets you
pretty close to the mark.

Graham.

graham said:

"Andre Jute" <[email hidden]> wrote in message

news:[email hidden]...

[email hidden] <[email hidden]> wrote:

Graham has already supplied a formula

We'll find out after you do the downhill test whether the Cd you
calculate predicts your maximum speed pedaling flat out along a flat
road, which is the point of having a Cd number. One thing is for sure:
if you merely want a cafe Cd closer to the 0.3 you dream of than the
c0.5 average (for 80 per cent of racing cyclists, say) that I suspect,
you're more likely to have your wish fulfilled with the downhill
shortcut than my method!

Andre,

I have read your article and would not argue with most of it. I do however
find your statement above about wish fulfillment a little harsh.

Joseph's a big boy, complete with intimidating three-day stubble. Ånd
maybe I'm just envious of his skintight red outfit, and the muscles
and the style to bring it off!

Quoted message said:

I have
conducted many of these tests in the past and after a good degree of
averaging I arrived at CdA figures as used in the formula I suggested to
Joseph of 0.51 riding with my hands on the hoods, 0.34 on the drops and 0.31
on my race bike on my tri bars (I am a veteran triathlete). Clearly when
doing such tests by far the biggest uncertainty is in determining the slope
of the hill which introduces considerable scatter in the results.

If , however, I plug the 0.31 number into a power calculation for my last
40km TT in 65 mins using the other data I gave in my example to Joseph
together with an overall drive train efficiency of 95% (obviously not needed
in a coast down calc) it has me putting out around 250W which does not seem
too bad for an old timer like me. If however I were to use your figure of
0.5 (assuming you mean the same as what Joseph and I mean by a CdA of 0.3
when you speak of a Cd of 0.5) that would put me closer to 350W for over a
hour which I think would be flattering indeed.

Graham.

I'm pretty veteran myself but in cycling terms I'm a potterer, not a
racer. (I put my heart rate at 80 per cent of max, and hold it there,
counting on my Cyber Nexus automatic gearbox to regulate my pace and
cadence up and down hills.) I transmogrified my formulation out of
automobile experience, as collected in a book I wrote for special car
builders -- rather fortunately as not too long after the book was
published I gave up cars altogether and would in the intervening years
have forgotten the formulae. (You know you're an old chappie when you
have to look up stuff -- in a book you wrote yourself!)

Cd is a dimensionless coefficient, in inherent quality of a shape (or
in this instance a contortion of the human shape which we assume the
rider can replicate precisely...). The A part is the frontal area of
the individual unit or person. CdA is the product of the two parts. We
would expect A to vary widely between cyclists, but Cd, for the same
position on the bike and assuming skintight clothes, to be much more
obviously close within reasonable limits. I add the qualification
because the radius of rounding is a factor in Cd and clearly really
large people have different edge radius than really small ones. So, to
answer your question more precisely, no, my Cd is not your CdA.
Example: Cd 0.3, frontal area 6sq ft or .5574 sq meter, so CdA is 1.8
in Imperial measure or .167 in metrics; whereas Cd is dimensionless,
CdA should always be accompanied by the measure of A. I don't quite
know how you get your numbers, but, approaching it from the back end,
if your check-result of 250W is reasonable, then your method and
terminology must be okay.

My guess for cyclists of Cd = 0.50 which bothers you still seems
reasonable to me, possibly on the low side of a conservative estimate.
An automobile must be awesomely well developed to reach a Cd of 0.3.
The human body is simply not an aerodynamic device, and in the
Aerodynamicists' Club hangs a Wanted Criminal poster for the man who
designed the safety bicycle. A person has only one advantage over a
car, aerodynamically speaking, and that is that his orifices are small
(as long as he's breathing through his nose); but that's more than
balanced by the bits sticking out (ears, elbows, legs). But then
again, I'm not a bicycle specialist, I'm extrapolating from automobile
experience, and you have your back-check. I'll wait to adjust my
opinion -- or take it up as an argument in search of evidence -- when
Joseph reports his results.

Either way I'm sure we'll advance our knowledge and have a spot of fun
doing it. Nice meeting you, Graham.

Andre Jute
http://members.lycos.co.uk/fiultra/BICYCLE%20HUMOUR.html

"Andre Jute" <[email hidden]> wrote in message
news:[email hidden]...

graham said:

"Andre Jute" <[email hidden]> wrote in message

news:[email hidden]...

[email hidden] <[email hidden]> wrote:

[Snip]

Either way I'm sure we'll advance our knowledge and have a spot of fun
doing it. Nice meeting you, Graham.

So long as it is fun then that's fine by me. There are far too many
"stressful" debates on this news group. You will by now have seen my
previous reply but to answer your query about my methodology it is all set
out in my original reply to Joseph. I have not attempted in the modelling I
have done to seperate out frontal area from drag coefficient but merely to
have derived their product from the formula I offered Joseph. I have toyed
with the idea of using photography to obtain an approximate measure of my
frontal area but never got round to it as the numbers for Cd x A I have
derived from my tests seem to be quite close which is what matters. As I see
it even if I could measure my frontal area how sure could I be of the value
of Cd to multiply it by?

Graham.

graham said:

In Joseph's case then the down hill method whilst not delivering "precision"
will allow him to do comparative tests on his position on the bike

If one were interested in doing comparative tests then precision would
be key. On the other hand, if the interest is in using CdA to get a
reasonable estimate of power, accuracy is more important.

Andre Jute said:

[...]
My guess for cyclists of Cd = 0.50 which bothers you still seems
reasonable to me, possibly on the low side of a conservative estimate.
An automobile must be awesomely well developed to reach a Cd of 0.3.

My 1994 Honda Civic Si had a reported Cd of 0.29.

Quoted message said:

The human body is simply not an aerodynamic device, and in the
Aerodynamicists' Club hangs a Wanted Criminal poster for the man who
designed the safety bicycle.[...]

Careful now, the dark side is calling.

Here is a model of bicycle that reportedly (based on recorded speed and
power meter data) has a Cd of less than 0.08:
<http://www.ent.ohiou.edu/~et181/hpv/lisa_Vetterlein.jpg>. Of course, it
is not usable on anything but a close course in low wind conditions.

--
Tom Sherman - Holstein-Friesland Bovinia
The weather is here, wish you were beautiful

Tom Sherman said:

Quoted message said:

[...]
My guess for cyclists of Cd = 0.50 which bothers you still seems
reasonable to me, possibly on the low side of a conservative
estimate. An automobile must be awesomely well developed to reach
a Cd of 0.3.

Quoted message said:

My 1994 Honda Civic Si had a reported Cd of 0.29.

Quoted message said:

Quoted message said:

The human body is simply not an aerodynamic device, and in the
Aerodynamicists' Club hangs a Wanted Criminal poster for the man
who designed the safety bicycle.[...]

Quoted message said:

Careful now, the dark side is calling.

Quoted message said:

Here is a model of bicycle that reportedly (based on recorded speed
and power meter data) has a Cd of less than 0.08:

http://www.ent.ohiou.edu/~et181/hpv/lisa_Vetterlein.jpg

Quoted message said:

Of course, it is not usable on anything but a close course in low
wind conditions.

This thread and the one about optimal spoke pattern is depressing to
me. It seems RBT has drifted into the "me too" syndrome of fans of
professional athletes. No one seems interested in enjoying bicycling
for itself but rather looking for ways of achieving world records.

Following that direction, "Bicycling in America" becomes more a way of
life:

http://draco.acs.uci.edu/rbfaq/FAQ/6.1.html

Wind effect has always been interesting in bicycling, but that is not
what this thread is about. To fill that gap for wind effects:

http://www.sheldonbrown.com/brandt/wind.html

Get out and enjoy the beauty of bicycling and forget about beating the
next guy in racing with special and more expensive equipment. There's
much more to bicycling than competition. In fact there's more to life
than the sports page.

For example:

http://www.paloaltobicycles.com/alps_photos.html

Jobst Brandt

Quoted message said:

This thread and the one about optimal spoke pattern is depressing to
me.  It seems RBT has drifted into the "me too" syndrome of fans of
professional athletes.  No one seems interested in enjoying bicycling
for itself but rather looking for ways of achieving world records.

I quite enjoy cycling just for the hell of it. That's why I do dumb
things like ride track bikes around on hilly roads. It's fun. But
racing is fun too, and in my case would be quite a bit more fun if I
didn't get dropped from every road race, or finish last in every time
trial. To acheive this I could either move someplace where there are
slower racers, or I can eliminate waste from my equipment and train to
become stronger. I chose the latter two. And that gives an enjoyment
in itself.

Quoted message said:

Get out and enjoy the beauty of bicycling and forget about beating the
next guy in racing with special and more expensive equipment.  There's
much more to bicycling than competition.  In fact there's more to life
than the sports page.

It doesn't have to be expensive. That TT bike in my pics has a $139
frame and used Sora equipment. Hardly expensive!

But I agree there is more than competition. For me competition is just
one facet. And as such, I cannot fathom why some of the folks I ride
with spend hours and hours at health clubs in the winter riding
stationary bikes.

Quoted message said:

For example:

http://www.paloaltobicycles.com/alps_photos.html

Beautiful.

Joseph