WIND
Jobst Brandt
Wind is the bicyclists greatest and invisible adversary, however,
being invisible doesn't mean it should remain a mystery.
By Jobst Brandt
Why small changes in wind direction seem to make large differences in
speed is not readily apparent and is why these effects are worth
analyzing. Of course wind seems to be just fine when coming from
behind, although that is not entirely true either but the opposite is
true when riding into a headwind, especially if it is gusty. Winds
often attack from directions other than straight ahead or behind but
side winds are not quite what they seem to be. Part of this
perception arises because wind speed and direction are difficult to
gauge by a moving observer.
It may seem that only headwinds slow us down, that side winds are only
a nuisance, and that tailwinds always help. This is not entirely
true. For instance, a direct side wind, at 90 degrees to the
direction of travel, always slows speed. Even a side wind slightly
from behind, one that is obviously from behind when standing still,
retards progress. These effects are what make this a subject
interesting and worth investigating.
When moving, a bicyclist experiences relative wind consisting of
riding through still air plus "real" wind (Fig 1). Wind drag
increases with the square of its velocity with respect to the rider
and this is what makes it so burdensome. That even a small increase
in speed without wind requires significantly more effort is a result
of this squared relationship between speed and drag.
Because aerodynamic drag increases as speed squared, doubling speed
quadruples drag, and being encountered at increased speed this drag
requires more power to overcome than the same drag would at lower
speed. For this reason power increases as the cube of rider speed.
For example, riding in still air on level ground at 25 miles per hour
requires almost twice the power than riding at 20 mph, even though
this is only 25 percent faster. Or more directly, doubling speed
requires eight times more power, regardless of initial speed. In
contrast, climbing a steep hill, typically at a speed where air drag
is insignificant, increasing speed by 25 percent requires 25 percent
more power.
Two other measurable power losses that occur, tire rolling resistance
and mechanical friction (chain and bearing friction) increase roughly
proportional to speed. As long as tires are reasonably inflated and
bearings lubricated, these losses are insignificant in comparison to
air drag even at high speeds.
Thus bicycling speed on level ground is governed almost solely by air
drag. Because drag increases rapidly with speed while power to
overcome it even faster, wind direction is difficult to assess. This
makes bicycling appear to always have headwinds. Unlike with cars,
where the gas pedal is depressed until a desired speed is attained,
the bicyclist is limited by power, so that his speed is limited by
prevailing winds. Bicycling speed levels off at the point where wind
drag power equals rider power. With this in mind, it's easy to see
how tailwinds can feel like headwinds once underway.
How rider and wind speed combine to generate drag is the question at
hand. Given the variables involved in riding in wind, determining
possible riding speed for winds from the side requires some geometry.
Considering two simple situations using the same rider power, one at
25 mph in still air on level ground and a second with a headwind of 25
mph. With the headwind, speed will slow to 11.6 mph because at this
speed the relative wind of 36.6 mph (25 + 11.6 mph) squared times the
speed of 11.6 is the same as 25 mph cubed (relative wind speed squared
times rider speed).
In contrast, a 25 mph tailwind would not increase speed to 50 mph as
might be expected, but rather to 46.7 mph, because at the higher
speed, air drag demands more power (work = force x distance, power =
work x rate). With constant power (that of 25 mph cubed), only 21.7
mph of additional wind (25 + 21.7 = 46.7) can be overcome, because
46.7 squared times 21.7 equals 25 cubed. Therefore, the greater the
speed the less drag can be overcome.
Applying a 25mph wind to a 50 mile out-and-back time trial for a rider
who would take two hours with no wind, the rider would take nearly two
hours and ten minutes battling the headwind at a speed of 11.6 mph,
while the tailwind portion would take little more than half hour for a
total elapsed time of 2:41.
If performance is not an issue, the power of relative headwinds
suggests not to fight them and be miserable, but rather to relax and
exert effort when the route changes direction and the winds are more
favorable.
Deciphering the effect of side winds is more complicated because a
direct side wind doesn't actually come from the side of a bicyclist in
motion. Its effect comes from the relative wind which, as was shown,
is a combination of the side wind and rider speed while the power
required is the in-line component of its drag times rider speed.
The relative wind is neither from straight ahead nor from the side,
but from an angle somewhere in between, and its velocity can be
greater than either of its components (Fig 1). The direction of the
relative wind can be found just as the sailor does with a thread tied
to the mast, however, this can be assessed analytically. By vector
addition of rider speed and wind speed, the magnitude and direction of
the relative wind can be found (Fig 1).
It might appear that side winds create more or less drag than direct
headwinds or tailwinds as a result of a different rider and bicycle
profile that determines a drag coefficient. Practically the
aerodynamic profile is the same from any direction Because all parts
of the rider, including arms, legs, torso and head, as well as all
major bicycle parts, are round. Using a round model called a bluff
body to compute drag power from any wind directions was verified in
the wind tunnel (Fig 2), and has been used for these calculations.
Fig 3. shows power required to overcome wind of various speeds from
all directions at at constant rider speed. The curves show power
required to ride as one would drive a car; that is, at the same speed
regardless of wind. This graph, as the others, is normalized to the
rider's speed so that the results are applicable to any rider at any
chosen speed. Thus, wind speeds are expressed as a percentage and
must be multiplied by rider speed. For example, at 20 mph rider
speed, the 80-percent wind curve means a wind blowing at 80 percent of
rider speed and shows what additional power must be expended at 20 mph
with a 16 mph wind (20 mph x 80 percent = 16 mph), blowing from
various directions.
-----------------------------------
Jobst Brandt
Mark Cleary
time has shown going out against the wind I never recover the time going
back. This is just what you stated and like running the best conditions
are level ground and zero wind. The only thing fun about wind is I just
love to run 10-20 miles into a headwind and then turnaround. The fun is
always much less time.
--
Deacon Mark Cleary
Epiphany Roman Catholic Church
Lou Holtman
In contrast of most people I like to start wind tailwind. I don't like
struggling against the wind in the beginning when I'm not warmed up.
Lou
Tom Ace
with the power calculations.
And where are the figures you refer to?
Tom Ace
datakoll
datakoll
> not up to analyzing friction vs index energy consumption ?
SEE PAGE 164-170
Ben C
> I'd be interested to see the analysis of side winds,
Well, he says it's just vector addition, but that doens't make sense to
me.
Suppose you're riding along at 30kph. Your speed is given by the vector
[30, 0]. With no "real" wind, your relative wind would be:
[0, 0] - [30, 0] = [-30, 0].
So let's say the wind is coming from the side at a speed of 20kph. So
the relative wind is now:
[0, 20] - [30, 0] = [-30, 20]
Sure we can work out the magnitude and angle of that relative wind, but
those aren't really relevant. The important thing is that it has a
horizontal component of -30, just like when there wasn't a side-wind,
obviously. So I don't see why it should slow you down any more than no
"real" wind according to this reasoning.
I think a side-wind possibly is worse than no wind in the real world,
but the reasons would be because of some more complicated aerodynamic
phenomena that aren't captured by just representing the wind as a
vector.
thirty-six
> I think a side-wind possibly is worse than no wind in the real world,
> but the reasons would be because of some more complicated aerodynamic
> phenomena that aren't captured by just representing the wind as a
> vector.
The front spokes, rim and forks etc, whisk up the air reducing the
drag over the legs in a headwind which they cannot do in a sidewind.
The just cause drag by whisking up the air and the drag over the legs
is more because of the angle they show to the wind. Anyway if you
use luggage, mount it high with the rider so as to reduce the frontal
area. Supposedly some of the old delivery bikes could go a fair
crack with a racer powering them and I believe this down to the basket
assisting aerodynamically. 1/2cwt meat would also help on the
downhill sections as did rod brakes on wet chrome rims. What a
delight it must have been.
carl...@comcast.net
Dear Ben,
See figure 4 and accompanying text:
http://www.tonyfoale.com/Articles/Aerodynamics/AERO.htm
Cheers,
Carl Fogel
Jobst Brandt
>> not up to analyzing friction vs index energy consumption ?
> SEE PAGE 164-170
How about you seeing those pages and extracting the pertinent text
yourself. I don't care for the library assignments on vague subjects.
I don't see what Ambrose Bierce has to offer on riding a bicycle with
or against wind. Besides that, your URL's are stretching the
capabilities of cut and paste. Try:
Jobst Brandt
Ben C
That's an interesting article.
It's more talking about stability there than why side-winds slow you
down, but it looks from figure 4 like the wake is bigger than in figure
1, and a bigger wake means more drag, as the article says.
Of course the drag in figure 4 is not pulling you straight backwards,
but partly to the side. But the backwards component could still end up
bigger than for a straight 75mph headwind.
pastor...@lanaifaith.com
"Jobst Brandt" <jbr...@sonic.net> wrote in message
news:4b095fb2$0$1583$742e...@news.sonic.net...
resistance against the rider came the inovatation of new cycling strategize,
componants and riding position to win the race.
http://www.youtube.com/watch?v=AyvwtOQYQ-E
I believe Jobst has posted this article before, I remember reading this or
similar post- good info.
I don't like side winds, my bike is sensitive to side winds for some reason.
As for headwinds, an intelligent wheel sucker knows how ride in such a way
as to avoid headwinds.
Tail winds are my favorite, but the return ride is the payback, it's a
pleasure and pain thing.
carl...@comcast.net
Dear Ben,
Two things matter in bicycle aerodynamics.
First, there's the apparent cross-section.
Duck your head and you reduce this. Let the wind come from the side
and it increases.
Far more important is the much trickier problem of what kind of wake
your cross-section generates--it takes power to generate turbulence,
whether straight back or to the sides.
To illustrate the two points, consider the Varna Diablo fully-faired
bike.
Technically, the faired bicycle has a larger cross-section than just
the rider in its frame.
But the disadvantage of the slightly larger cross-section is dwarfed
by the aerodynamic smoothness achieved by the fairing, which generates
far less turbulence than the messy rider, pedals, wheels, and so on.
Again, it's the simple act of generating turbulent air that causes the
drag, with the direction not being as important as you might think.
Watch a car cruising at about 20 mph down the street on a quiet fall
day, and you'll see the turbulence swirling the leaves off the
pavement to either side. Generating the swirling air currents takes
power.
Or just flip a bike upside-down and spin the rear wheel up--you can
feel the turbulence from the spokes off to the sides.
A bigger wake, symmetrical or lopsided, means that more power was
wasted.
Cheers,
Carl Fogel
thirty-six
> "Jobst Brandt" <jbra...@sonic.net> wrote in message
> I believe Jobst has posted this article before, I remember reading this or
> similar post- good info.
> I don't like side winds, my bike is sensitive to side winds for some reason.
> As for headwinds, an intelligent wheel sucker knows how ride in such a way
> as to avoid headwinds.
Why do you think we moan when someone isn't wearing mudguards despite
there being no rain nor forcast of it? Because it permits closer
ridiing (as long as any wire ends are clipped short) and getting
behind someone with Salmon guards is ideal.
(PeteCresswell)
>In contrast of most people I like to start wind tailwind. I don't like
>struggling against the wind in the beginning when I'm not warmed up.
Also, maybe there's an attraction to the gambler's spirit: ride
out with the wind, and maybe it will shift or die in time to make
the ride home easier.
--
PeteCresswell
Ben C
Yes, although some of that power is coming from the wind itself, not
necessarily out of the car's engine.
> Or just flip a bike upside-down and spin the rear wheel up--you can
> feel the turbulence from the spokes off to the sides.
>
> A bigger wake, symmetrical or lopsided, means that more power was
> wasted.
Yes that sounds very plausible. In a side wind, one can imagine that
you end up with a larger wake behind you than when there is no wind.
Even a side wind which is coming slightly from behind may result in more
wake behind you.
datakoll
WORDS FAIL ME !
Andre Jute
rec.bicycles.tech
Ben C <spam...@spam.eggs> wrote:
> I think a side-wind possibly is worse than no wind in the real world,
> but the reasons would be because of some more complicated aerodynamic
> phenomena that aren't captured by just representing the wind as a
> vector.
This is correct. I'll explain in a moment.
First, Jobst is talking of an idealized situation, as indicated by his
remarks about the profile of human building blocks presented to the
wind being round, ditto bike tubes. The ideal aerodynamic shape in
section is a very fat teardrop truncated a long way from the thin end.
A round section is next best.
Except -- and this is where you come in -- to side winds. The
untruncated teardrop shape is very unstable in side winds, and the
cutoff Kamm profile, while better, is still much less stable in winds
off the quarters than from the front or the back.
The counterintuitive truth is that the more aerodynamically
incompetent a shape is in longitudinal section and plan, the better it
will handle wind off the longitundinal axis.
That is why automobiles, no matter how aerodymically smooth in the
longitudinal section and often plan, often have what appears to be
slab sides with very small radii, especially onto the roof and the
floor. These matters are to improve their stability in crosswinds.
Remember the VW Kombi, a brickshaped vehicle from the first Beetle
days? That was a vehicle which for its height was actually very stable
in crosswinds. (It was less incompetent than it appeared to the
aerodynamically naieve in several other aspects as well, careful
radiusing taking care of the inherent ills of the brick shape, and the
brick shape's removal of the centre of aerodynamic pressure to over
the rear axle being a very great benefit at speed in crosswinds.)
*****
Any disturbance in the laminar flow of air consumes power additional
to merely driving the notional frontal CdA. With a cyclist, whose
vehicle and exposed body are the inescapably the "wrong" shape for any
but perpendicular winds, winds from the quarters cost proportionately
more than in a correctly shaped powered vehicle. Thus Jobst's
idealized calculations are likely to be further off the simple vector-
addition when calculating for side winds than when calculating for a
wind from the front or the rear.
Thus, while I would put some faith in calculations by known careful
and experienced people of facing or following winds, I am of the
opinion that winds from any quarter/aero resistance/power requirement
would be better determined empirically.
Who's got a wind tunnel Ben and I can borrow over a weekend?
*****
As an aside, thrown in for discussion, I believe a roadracer might
well be more aerodynamic going backwards than going forwards, even
with his streamlined helmet. Air getting into the crook of his legs,
even churned as it would be, would be less of a block than the near-
solid mass of air captured under his torso at the crook of his hips as
he settles to the classic flat back posture.
*****
BTW, on the page Fogel refers us to, the drawing of aerodynamic shapes
passing air seems to have originated, possibly indirectly, in my book
Designing and Building Special Cars. Always flattering to see one's
influence being dissemminated.
Andre Jute
The whispering wind in the willows
Dan O
As a commuter I generally don't have much choice in the matter, but
fortunately, for much of the year the wind is calm in the mornings,
then generally helpful to me in the afternoons.
However, this time of year, while I may get a tailwind in the morning
at least as often as not, I often face headwinds (sometimes tough ones
- sometimes compounded by cold rain) in darkness on the way home. At
times like these I just think to myself, "what if I *always* faced
headwinds like this", and the realization that of course I won't is
reassuring and helps me through. (This works for tough hills, too -
what if I had to keep climbing and climbing and climbing forever - and
never, ever crest this hill?)
There are the rare days when the tailwind pushes me in the morning,
then comes around and pushes me home, too. Conversely, though, there
are the other days.
As a practical matter, dynamic wind effects are highly variable
depending on topography and other windbreaks, and it's rarely as bad
as it could be. It does help to relax and not fight it. If you see
the weather as your enemy, you're going to lose (or more probably give
up).
Dan O
> On 2009-11-22, carlfo...@comcast.net <carlfo...@comcast.net> wrote:
>
>
>
> > On Sun, 22 Nov 2009 15:14:11 -0600, Ben C <spams...@spam.eggs> wrote:
>
> >>On 2009-11-22, carlfo...@comcast.net <carlfo...@comcast.net> wrote:
You know what's really remarkable about the wake of cars and
(especially) trucks: How very warm it is.
> > Or just flip a bike upside-down and spin the rear wheel up--you can
> > feel the turbulence from the spokes off to the sides.
>
> > A bigger wake, symmetrical or lopsided, means that more power was
> > wasted.
>
> Yes that sounds very plausible. In a side wind, one can imagine that
> you end up with a larger wake behind you than when there is no wind.
>
> Even a side wind which is coming slightly from behind may result in more
> wake behind you.
I like a side wind... because it's not a headwind :-)
Frank Krygowski
> RIDING IN THE WIND
Some comments:
> Two other measurable power losses that occur, tire rolling resistance
> and mechanical friction (chain and bearing friction) increase roughly
> proportional to speed. As long as tires are reasonably inflated and
> bearings lubricated, these losses are insignificant in comparison to
> air drag even at high speeds.
This article, like most, omits any mention of suspension losses. Too
bad. I think Jan Heine has adequately demonstrated that they can be
very large - about as bad as dealing with a strong headwind.
Yes, one can say it's simply not part of the discussion; but since the
article mentions weight (when climbing), mechanical friction and
"rolling resistance" one might think it's listing all important
losses.
But since Jobst has elsewhere said rolling resistance does not include
suspension losses, an important factor is being given short shrift.
> Considering two simple situations using the same rider power, one at
> 25 mph in still air on level ground and a second with a headwind of 25
> mph. ...
> In contrast, a 25 mph tailwind would not increase speed to 50 mph as
> might be expected, but rather to 46.7 mph, because at the higher
> speed, air drag demands more power (work = force x distance, power =
> work x rate).
And in real life, I believe speed would be even less. Spokes churn
the air even when relative wind is zero, and this consumes power.
I recall having that demonstrated by a Human Powered Vehicle
enthusiast. He was showing the value of covering the spokes even with
a wheel inside a fully faired recumbent bike. With the bike
stationary, cranking a spoked wheel up to speed caused quite a breeze,
but a covered (or disk) wheel caused very little.
> The direction of the
> relative wind can be found just as the sailor does with a thread tied
> to the mast, however, this can be assessed analytically. By vector
> addition of rider speed and wind speed, the magnitude and direction of
> the relative wind can be found (Fig 1).
Yep. I used to have a set of Scott aero bars on my touring bike. I
tied a thread to the highest, most forward point on the bars. I used
it as a tool to help my wife and/or daughter draft me, i.e. to find
the best part of my wind shadow.
One final note: In _Bicycle Quarterly_ a few issues ago, Jan Heine
reported on some wind tunnel tests. He pointed out that crouching
down to the drops, etc. certainly reduced drag, but that all the
effect was due to reduction of frontal area. The drag coefficient
didn't drop at all. Seems we can't make ourselves really
"streamlined" by changing our position. At least, not on a more or
less standard bike.
But J.Heine also tested a fairly crude cardboard fairing mounted just
in front of the handlebars. He seemed surprised that it didn't help
at all, despite the fact that he made its upper surface slant upwards
- supposedly, to "direct the air [up about two feet] over the rider's
shoulders."
One might say he seemed to be envisioning air to have much more
inertia than it has, as if a slight upward push would cause it to rise
a great detail. More generally, air goes where its own physics
directs it, not where the arrows on our design sketches tell it to go!
- Frank Krygowski
carl...@comcast.net
<frkr...@gmail.com> wrote:
[snip]
>One final note: In _Bicycle Quarterly_ a few issues ago, Jan Heine
>reported on some wind tunnel tests. He pointed out that crouching
>down to the drops, etc. certainly reduced drag, but that all the
>effect was due to reduction of frontal area. The drag coefficient
>didn't drop at all. Seems we can't make ourselves really
>"streamlined" by changing our position. At least, not on a more or
>less standard bike.
>
>But J.Heine also tested a fairly crude cardboard fairing mounted just
>in front of the handlebars. He seemed surprised that it didn't help
>at all, despite the fact that he made its upper surface slant upwards
>- supposedly, to "direct the air [up about two feet] over the rider's
>shoulders."
>
>One might say he seemed to be envisioning air to have much more
>inertia than it has, as if a slight upward push would cause it to rise
>a great detail. More generally, air goes where its own physics
>directs it, not where the arrows on our design sketches tell it to go!
>
>- Frank Krygowski
Dear Frank,
Other people seem to have been able to achieve noticeable drag
reductions with fairly crude front fairings:
"It is noteworthy in table 4.3 that worthwhile drag reductions were
given by partial fairings such as those shown in figures 4.6 and 4.7.
(In some cases these were simply curved sheets mounted on the
handlebars.) The principal reason for this kind of drag reduction
appears to be the reduction of the effective area. Without any
fairing, the air billows out around the rider's bluff body, disturbing
air over an area much greater than that of of the body alone. An
upstream streamlined shape (such as a partial fairing) can reduce this
disturbance. A partial fairing can also have a favorable distribution
of pressure. The effective drag coefficient for a front fairing, such
as the lowest one in figure 4.8, can actually be negative (ref. 2,
p.312)."
--"Bicycling Science," 2nd edition, p.97
The tables and illustrations:
http://i46.tinypic.com/6gedky.jpg
Reference 2 is to Hoerner's "Fluid Dynamic Drag."
Cheers,
Carl Fogel
Gennaro
[...]
> Dear Ben,
>
> See figure 4 and accompanying text:
> http://www.tonyfoale.com/Articles/Aerodynamics/AERO.htm
I don't seem to agree with figure 4 and accompanying text.
It is true that the rectangle would generate small "sideways"
force and large "longitudinal" force, but these directions are
relative to the wind (not to the vehicle); the result, in this case,
is that the aerodynamic force would have roughly the same
direction as the 'effective' windspeed.
In the case of figure 4, the "sideways force" (relative to the
vehicle this time) is small because the 'angle of incidence' is
small; if this angle were larger (as in the case of strong
sidewind for a cyclist, say a sidewind of 50 mph for somebody
travelling at 20mph) the "sideways force" mentioned
above would be quite larger.
As noted in the past, Jobst indeed assumes that the
aerodynamic force has the same direction as the relative
wind, but ignores altogether the component normal to the
direction of the vehicle.
> Cheers,
>
> Carl Fogel
bye
Gennaro
Gennaro
[...]
> Well, he says it's just vector addition, but that doens't make sense to
> me.
>
> Suppose you're riding along at 30kph. Your speed is given by the vector
> [30, 0]. With no "real" wind, your relative wind would be:
>
> [0, 0] - [30, 0] = [-30, 0].
>
> So let's say the wind is coming from the side at a speed of 20kph. So
> the relative wind is now:
>
> [0, 20] - [30, 0] = [-30, 20]
>
> Sure we can work out the magnitude and angle of that relative wind, but
> those aren't really relevant. The important thing is that it has a
> horizontal component of -30, just like when there wasn't a side-wind,
> obviously.
As a matter of fact, this is not the case.
The intensity of the aerodynamic force is proportional to the square
of the "relative" wind speed. So, once you have calculated the
magnitude of the relative wind you have to square it (and multiply
it by some coefficients) to know the intensity of the aerodynamic
force.
If you suppose that the force has the same direction as the wind
speed you can then decompose it in its components normal
and parallel to the direction of the bike.
[...]
bye
Gennaro
Ron
> On Sun, 22 Nov 2009 17:05:09 -0800 (PST), Frank Krygowski
>
Carl,
Where is figure 4.8 in the picture? Interesting, thanks for sharing.
pm
The vector certainly does capture one reason why side winds are worse
than still air. What you're missing here is that the force from wind
is nonlinear in terms of the wind velocity. Wind resistance scales
with the square of relative air velocity for the ranges of speeds
we're talking about. So take your example. Going 30 kmh in still air,
you have a relative wind of:
[-30, 0], which has an absolute magnitude of 30 kmh, which leads to a
wind force of:
[900, 0] * C * kph^2
where C is a constant involving your coefficient of drag, fluid
density and frontal surface area. (C*kph^2) is a unit of force; I'll
just call it a "drag unit."
Now consider your 20kph side wind. Your relative air speed is now
[-30, 20] which has an absolute magnitude of 36.05 kph. The magnitude
of the wind force is related to the square of that; so 1300 drag
units. Those 1300 drag units are directed along the relative wind
vector, so the force pushing on you is
[-30,20]/36.05*1300, or
[1081, 721]
As you rightly point out, you don't care about the sideways component
of the drag force. but the backwards component of the wind drag (1081)
IS greater than the 900 drag units you had in still air. That's aside
from any effects of having a bigger wake, etc.
-pm
carl...@comcast.net
wrote:
Dear Ron,
Figure 4.6 is the photo of the chest-level Campbell wrap-around
fairing.
Figure 4.7 is the drawing of the Windfoiler see-through face-high
front-only fairing
Figure 4.8 is the vertical series of diagrams and partial drag
coefficients, from 0.8 to -0.05, taken from Hoerner's "Fluid
Dynamics."
Cheers,
Carl Fogel
Ben C
OK, so using this example, my relative wind of [-30, 20] has a magnitude
of 36kph. So a force of something proportional to 1296 (36*36=1296).
So as a force vector, I could write it [-1078.35, 718.90] (multiplied by
some coefficient to get actual N).
But without the side-wind, my force vector would be [-900, 0] (just
squaring the 30).
So I'm experiencing a force of 1078 pushing me back rather than of 900.
Is this right?
Ben C
Yes, thanks for your help and that of Gennaro. I got similar numbers
when I tried to work this out for myself.
This explains what Jobst is talking about and what I was missing (even
if there's more to wind than that as people have been discussing in
other posts).
Frank Krygowski
>
Oh, it's certainly possible to get reduced drag without a full
enclosure! In the past, I've ridden some (mostly in winter) with a
Zipper fairing, which is basically a big plastic bubble, roughly two
feet diameter. It definitely provided some benefit, demonstrated by
my coasting speed down the big hill into work; but IIRC the literature
claimed it measurably reduced drag only if you were crouched on the
drops. The instructions said you were in the right position if you
heard the air sort of rumbling past your ears as it flowed over the
top of the fairing.
Also, I once toured with a friend whose bike was identical to mine but
for a smaller frame size. Our loads were the same, our weights were
the same and I was several inches taller. But I outcoasted him easily
on every downhill, almost certainly because he was using standard
(squarish) Cannondale panniers, and I was using Specialized Tailwind
panniers, which were designed to be more streamlined and cause less
drag.
I couldn't find that copy of Bicycle Quarterly just now, but IIRC the
fairing Jan Heine tested was roughly 1/3 the size of what's shown in
the Bicycling Science photos and sketches.
- Frank Krygowski
Tom Ace
> Yes, thanks for your help and that of Gennaro. I got similar numbers
> when I tried to work this out for myself.
>
> This explains what Jobst is talking about and what I was missing (even
> if there's more to wind than that as people have been discussing in
> other posts).
I join in saying thanks to those who've helped explain this here.
Tom Ace
Andy Coggan
> It might appear that side winds create more or less drag than direct
> headwinds or tailwinds as a result of a different rider and bicycle
> profile that determines a drag coefficient. Practically the
> aerodynamic profile is the same from any direction Because all parts
> of the rider, including arms, legs, torso and head, as well as all
> major bicycle parts, are round. Using a round model called a bluff
> body to compute drag power from any wind directions was verified in
> the wind tunnel (Fig 2), and has been used for these calculations.
The "bluff body" assumption is a gross oversimplification.
Andy Coggan
Jobst Brandt
I think deciphering what is meant by bluff body is important in this
discussion. A bluff body (the rider and his bicycle) are essentially
round cross sections who's drag is governed more by cross sectional
shape rather than orientation to the wind, having no airfoil tear-drop
streamlining. Therefore, the bluff body has similar drag in all
directions (in line-, cross-, and tailwinds.)
http://www.efluids.com/efluids/pages/bicycle.htmop
Jobst Brandt
Andy Coggan
...which is not true for many cyclists.
Andy Coggan
thirty-six
I wonder for Chalo's opinion.
Tom Sherman °_°
Especially those with fairings.
--
Tom Sherman - 42.435731,-83.985007
I am a vehicular cyclist.
thirty-six
wrote:
what about red heads
Ben C
> Re: WIND
> rec.bicycles.tech
>
> Ben C <spam...@spam.eggs> wrote:
>
>> I think a side-wind possibly is worse than no wind in the real world,
>> but the reasons would be because of some more complicated aerodynamic
>> phenomena that aren't captured by just representing the wind as a
>> vector.
> Any disturbance in the laminar flow of air consumes power additional
> to merely driving the notional frontal CdA. With a cyclist, whose
> vehicle and exposed body are the inescapably the "wrong" shape for any
> but perpendicular winds, winds from the quarters cost proportionately
> more than in a correctly shaped powered vehicle. Thus Jobst's
> idealized calculations are likely to be further off the simple vector-
> addition when calculating for side winds than when calculating for a
> wind from the front or the rear.
One thing I'm not clear about is this: it's often said that aerodynamic
force is proportional to speed squared. This is a bit of an
approximation, but what exactly is it approximating? Presumably just
measured results? In that case, presumably it already takes into account
the effect of the wake.
You don't get the force proportional to speed squared _plus_ the effect
of the wake, you just get the effect of the wake, which _is_
approximately a force proportional to speed squared?
Tom Sherman °_°
> [...]
> what about red heads
<http://upload.wikimedia.org/wikipedia/commons/6/64/RL_1958_Ferrari_250_Testa_Rossa_34.JPG>
AMuzi
>> [...]
>> what about red heads
Tom Sherman �_� wrote:
> <http://upload.wikimedia.org/wikipedia/commons/6/64/RL_1958_Ferrari_250_Testa_Rossa_34.JPG>
PsyOps. The wind runs in fear from her.
--
Andrew Muzi
<www.yellowjersey.org/>
Open every day since 1 April, 1971
Andre Jute
Supposing an aerodymic body, the Cd determined either empirically or
by guesswork holds only when the wind is dead ahead. Then the velocity
squared formula holds without reference to the turbulence in the wake
which, as you say, is included.
However, an aerodynamic body from the rear has a different Cd and if
it is not measured empirically in a wind tunnel, the calculation must
include a large factor for turbulence. If the wind is from the side,
where it is not aerodynamic at all, the factor might have to be very
large. From the sides, radiusing is critical; fractions of an inch
make appreciable, measurable differences.
That is why Jobst makes a point of the roundness of a cyclist's limbs
and the tubes on his bike, because that might lower the constant in
the formula when it comes to calculating Cd for winds from anywhere
but straight ahead; the idealized vector addition Jobst is promoting
abstracts from the most difficult part of the job, determining Cd.
We might observe that an old-fashioned bike like Jobst's is probably
much more stable to any side wind than a modern "aero" bike with its
tubes ovalized in the fore-aft direction.
Andre Jute
"Cycling wisdom" is an oxymoron
thirty-six
wrote:
> thirty-six aka someone aka Nick L Plate aka Trevor Jeffrey wrote:
>
> > [...]
> > what about red heads
>
>
With a set of Rudge - Borrani wire wheels.
Chalo
>
> Andy Coggan wrote:
> >
> > Jobst Brandt wrote:
> > >
> > > I think deciphering what is meant by bluff body is important in this
> > > discussion. A bluff body (the rider and his bicycle) are essentially
> > > round cross sections who's drag is governed more by cross sectional
> > > shape rather than orientation to the wind, having no airfoil tear-drop
> > > streamlining. Therefore, the bluff body has similar drag in all
> > > directions (in line-, cross-, and tailwinds.)
> >
> > ...which is not true for many cyclists.
>
> I wonder for Chalo's opinion.
I'm more aerodynamic than other cyclists (I roll much faster
downhill), but I assume that's a simple matter of mass:frontal area.
Well, that and impressive overall smoothness. Heh.
Chalo
datakoll
Gennaro
[...]
> One thing I'm not clear about is this: it's often said that aerodynamic
> force is proportional to speed squared.
Drag D = .5 * rho* S * cd * v^2
where rho is fluid density, S front surface cd drag coefficient, v airspeed.
> This is a bit of an approximation, but what exactly is it
> approximating?
Under some simplifying assumption, from balance of momentum you
get Bernoulli's theorem:
p + .5*rho*v^2 = const. [p=pressure].
If you blew on a wall of surface S you could ideally exert on it a force
F = .5*rho*v^2*S
with the use of cd you compare this "ideal" force with what happens in
reality.
cd depends on the shape of the body and, notably, on Reynolds
number but it can be considered constant for cycling applications.
The aerodynamic force is the integral over the whole surface of
the body of pressure and friction forces.
For a flat plate orthogonal to the stream, for example, the
aerodynamic force will be the sum of the forces acting on
the front and on the back of the plate. When you blow
over such a plate (see video below at 1:34)
www.youtube.com/watch?v=ouF9Xkoi3uk
flow separates at the edges of the plate causing behind it
a large wake in which the pressure is even lower than
static pressure, resulting in a cd greater than one.
An aerofoil is designed in such a way that the flow separates
as late as possible:
www.youtube.com/watch?v=6UlsArvbTeo
on the forward part air "pushes" the aerofoil backwards, but on
its rear part the aerofoil is actually "pushed" forwards. This partial
pressure recovery stops as the flow separates (in the
wake there is no pressure recovery) and the drag force increases.
This is seen very well in the video linked above starting from 0:51.
cd for an aerofoil can be quite low (0.05 and less).
For a flow around a bluff body, such a sphere or a cylinder
www.youtube.com/watch?v=7KKFtgx2anY
the flow always separates and we have a wide range of cd,
let's say from 0.4 to 1.1 for speeds of interest.
cd can in some cases be found analytically but in
practical situations is usuuall calculated empirically.
For non faired bicycles, according to "Bicycling Science" cd
varies from 0.88 for racing bikes with crouched rider to
1.15 for upright commuting bikes.
> Presumably just measured results? In that case,
> presumably it already takes into account the effect of the wake.
As explained above, the wake causes lower pressure on the rear
surface of the body and is "automatically" taken into account when
calculating the cd
[...]
bye
Gennaro
Gennaro
http://www.efluids.com/efluids/pages/bicycle.htm
Even if a cylinder is indeed a bluff body, a bluff body is by no
menas whatsoever bound to have round cross section (a brick
is a bluff body!), as properly explained in the web pages that
you yourself linked above.
Furthermore, a bluff body does not necessarily have a drag
coefficient independent of flow direction - see for example
cube and angled cube here:
http://en.wikipedia.org/wiki/Drag_coefficient
It would be good if you strived to avoid such gross inaccuracies
in your "didactic" posts.
I do understand that it is tempting to model a cyclist+bike as a series
of vertical cylinders so that they all look the same from any direction
of the air, wrap this assumption under a (misleading) "technical" term,
and give it as an explanation why cd for a bike is essentially the same
in any direction, but this shouldn't be done. (I don't know if this is the
case, but it might actually vary only slightly with direction)..
> Jobst Brandt
Gennaro
Jobst Brandt
>>> I think a side-wind possibly is worse than no wind in the real
>>> world, but the reasons would be because of some more complicated
>>> aerodynamic phenomena that aren't captured by just representing
>>> the wind as a vector.
> [...]
>> Any disturbance in the laminar flow of air consumes power
>> additional to merely driving the notional frontal CdA. With a
>> cyclist, whose vehicle and exposed body are the inescapably the
>> "wrong" shape for any but perpendicular winds, winds from the
>> quarters cost proportionately more than in a correctly shaped
>> powered vehicle. Thus Jobst's idealized calculations are likely to
>> be further off the simple vector- addition when calculating for
>> side winds than when calculating for a wind from the front or the
>> rear.
> One thing I'm not clear about is this: it's often said that
> aerodynamic force is proportional to speed squared. This is a bit
> of an approximation, but what exactly is it approximating?
> Presumably just measured results? In that case, presumably it
> already takes into account the effect of the wake.
With bluff bodies, it is accurate and has been measured. Only
streamlined bodies diverge from that rule.
> You don't get the force proportional to speed squared _plus_ the
> effect of the wake, you just get the effect of the wake, which _is_
> approximately a force proportional to speed squared?
and power is speed cubed as the article explicitly states. It also
shows wind tunnel data in comparison to the computed values.
Jobst Brandt
Jobst Brandt
>>> I think a side-wind possibly is worse than no wind in the real
>>> world, but the reasons would be because of some more complicated
>>> aerodynamic phenomena that aren't captured by just representing
>>> the wind as a vector.
> [...]
>> Any disturbance in the laminar flow of air consumes power
>> additional to merely driving the notional frontal CdA. With a
>> cyclist, whose vehicle and exposed body are the inescapably the
>> "wrong" shape for any but perpendicular winds, winds from the
>> quarters cost proportionately more than in a correctly shaped
>> powered vehicle. Thus Jobst's idealized calculations are likely to
>> be further off the simple vector- addition when calculating for
>> side winds than when calculating for a wind from the front or the
>> rear.
> One thing I'm not clear about is this: it's often said that
> aerodynamic force is proportional to speed squared. This is a bit
> of an approximation, but what exactly is it approximating?
> Presumably just measured results? In that case, presumably it
> already takes into account the effect of the wake.
With bluff bodies, it is accurate and has been measured. Only
streamlined bodies diverge from that rule.
> You don't get the force proportional to speed squared _plus_ the
> effect of the wake, you just get the effect of the wake, which _is_
> approximately a force proportional to speed squared?
and power is speed cubed as the article explicitly states. It also
shows wind tunnel data in comparison to the computed values.
http://www.sheldonbrown.com/brandt/wind.html
Jobst Brandt
Andy Coggan
> I do understand that it is tempting to model a cyclist+bike as a series
> of vertical cylinders so that they all look the same from any direction
> of the air, wrap this assumption under a (misleading) "technical" term,
> and give it as an explanation why cd for a bike is essentially the same
> in any direction, but this shouldn't be done. (I don't know if this is the
> case, but it might actually vary only slightly with direction)..
It had long been known that the Cd of a cyclist varies with wind
direction. Jobst just refuses to accept it.
Andy Coggan
Michael Press
"(PeteCresswell)" <x...@y.Invalid> wrote:
> Per Lou Holtman:
> >In contrast of most people I like to start wind tailwind. I don't like
> >struggling against the wind in the beginning when I'm not warmed up.
>
> Also, maybe there's an attraction to the gambler's spirit: ride
> out with the wind, and maybe it will shift or die in time to make
> the ride home easier.
Yes.
--
Michael Press
Ben C
> "Ben C" wrote...
>
> [...]
>> One thing I'm not clear about is this: it's often said that aerodynamic
>> force is proportional to speed squared.
>
> Drag D = .5 * rho* S * cd * v^2
> where rho is fluid density, S front surface cd drag coefficient, v airspeed.
>
>> This is a bit of an approximation, but what exactly is it
>> approximating?
>
> Under some simplifying assumption, from balance of momentum you
> get Bernoulli's theorem:
> p + .5*rho*v^2 = const. [p=pressure].
I see. I also found this which explains it quite well:
http://scienceworld.wolfram.com/physics/BernoullisLaw.html (with some
extra terms for gravity).
I never knew how the v^2 was derived.
> If you blew on a wall of surface S you could ideally exert on it a force
> F = .5*rho*v^2*S
> with the use of cd you compare this "ideal" force with what happens in
> reality.
>
> cd depends on the shape of the body and, notably, on Reynolds
> number but it can be considered constant for cycling applications.
>
> The aerodynamic force is the integral over the whole surface of
> the body of pressure and friction forces.
>
> For a flat plate orthogonal to the stream, for example, the
> aerodynamic force will be the sum of the forces acting on
> the front and on the back of the plate. When you blow
> over such a plate (see video below at 1:34)
> www.youtube.com/watch?v=ouF9Xkoi3uk
> flow separates at the edges of the plate causing behind it
> a large wake in which the pressure is even lower than
> static pressure, resulting in a cd greater than one.
OK. It seems initially like a Cd > 1 should violate conservation of
energy based on the derivation of Bernoulli's law.
I guess what's really happening is that the velocity of the air at the
front of the plate is actually higher than v, because it's being sucked
around to the back of the plate by the lower pressure there.
But we just factor that into Cd instead because it's easier.
> An aerofoil is designed in such a way that the flow separates
> as late as possible:
> www.youtube.com/watch?v=6UlsArvbTeo
> on the forward part air "pushes" the aerofoil backwards, but on
> its rear part the aerofoil is actually "pushed" forwards. This partial
> pressure recovery stops as the flow separates (in the
> wake there is no pressure recovery) and the drag force increases.
> This is seen very well in the video linked above starting from 0:51.
> cd for an aerofoil can be quite low (0.05 and less).
>
> For a flow around a bluff body, such a sphere or a cylinder
> www.youtube.com/watch?v=7KKFtgx2anY
> the flow always separates and we have a wide range of cd,
> let's say from 0.4 to 1.1 for speeds of interest.
>
> cd can in some cases be found analytically but in
> practical situations is usuuall calculated empirically.
>
> For non faired bicycles, according to "Bicycling Science" cd
> varies from 0.88 for racing bikes with crouched rider to
> 1.15 for upright commuting bikes.
>
>> Presumably just measured results? In that case,
>> presumably it already takes into account the effect of the wake.
>
> As explained above, the wake causes lower pressure on the rear
> surface of the body and is "automatically" taken into account when
> calculating the cd
Yes, I see that now. I guess it includes friction as well?
Michael Press
Ben C <spam...@spam.eggs> wrote:
> One thing I'm not clear about is this: it's often said that aerodynamic
> force is proportional to speed squared. This is a bit of an
> approximation, but what exactly is it approximating? Presumably just
> measured results? In that case, presumably it already takes into account
> the effect of the wake.
>
It is based on a simple model invoking only the kinetic theory
of gasses. The cyclist runs into an air molecule. The air
molecule gains speed from the collision. The gain in speed
is proportional to the speed of the cyclist. The energy gained
by the air molecule is proportional to the square of the speed
gained. The number of molecules bouncing off per unit time
is proportional to the speed. Therefore the power dissipation
to air drag is proportional to the the square of the speed
times the speed: it is proportional to the cube of the speed.
--
Michael Press
datakoll
Michael Press
<47f439ec-8dd9-4b02...@y28g2000prd.googlegroups.com>,
datakoll <data...@yahoo.com> wrote:
> PLANNING A TRIP ?
>
> noaa weather service
>
> and
>
> http://...
What are you talking about?
--
Michael Press
Andre Jute
> In article
> <47f439ec-8dd9-4b02-98ef-05011e93e...@y28g2000prd.googlegroups.com>,
>
> datakoll <datak...@yahoo.com> wrote:
> > PLANNING A TRIP ?
>
> > noaa weather service
>
> > and
>
> > http://...
>
You're assuming even Gene knows what he intends to say. -- AJ
datakoll
course, replace hoop snakes, overall knowledge for wind directions
and speeds are applicable or in an evolutionary path, the converse.
the Reaper, right ?
datakoll
Andre Jute
Yes. Quite. About the evolutionary path, I mean.
About wind direction I like empirical tests; the problem is that wind
tunnel time is atrociously expensive. Unlike others here, I think
Jobst has a point about bluff bodies being a (probably) reasonable
approximation. Where I part company from him is where of late he has
seemed to claim the bluff body is a directly comparable substitute; I
am pretty sure some judgement would still be involved, and a fudge
factor or two.
Experience is just another name for having a knack for fudge factors,
though on my CV (never had one but if I ever needed one) I would call
it fine judgement or even discrimination.
> the Reaper, right ?
You're too young to be so familiar with him, son. Call him "Mr
Reaper".
Andre Jute
"The brain of an engineer is a delicate instrument which must be
protected against the unevenness of the ground." -- Wifredo-Pelayo
Ricart Medina
Andre Jute
> sometimes, I consider a vow of silence an effective approach
!
Bill Sornson
You ended a sentence with a preposition.
BS
datakoll
surly. THE REAPER is a painting(s) from Winslow Homer
Dan O
Commuting quite a distance nearly every day, NOAA observations and NWS
analysis and modeling are some of my most appreciated information
resources.
AMuzi
> "use preps sparsely, there are few between"
> surly. THE REAPER is a painting(s) from Winslow Homer
Oh. I thought you meant "reaper":
http://www.epilogue.net/cgi/database/art/view.pl?id=85314
carl...@comcast.net
>datakoll wrote:
>> "use preps sparsely, there are few between"
>> surly. THE REAPER is a painting(s) from Winslow Homer
>
>Oh. I thought you meant "reaper":
>http://www.epilogue.net/cgi/database/art/view.pl?id=85314
Dear Andrew,
Oh, I thought you meant Van Gogh.
Arles, June, 1888, Wheat stacks with reaper:
http://www.vangoghgallery.com/catalog/Painting/759/Wheat-Stacks-with-Reaper.html
Saint-R�my, June, 1889, Wheat field with reaper and sun:
http://www.vangoghgallery.com/catalog/Painting/750/Wheat-Field-with-Reaper-and-Sun.html
Saint-R�my, September, 1889, Wheat field behind St. Paul-Hospital with
a reaper:
Saint-R�my, September, 1889, Wheat field with reaper at sunrise:
http://www.vangoghgallery.com/catalog/Painting/757/Wheat-Fields-with-Reaper-at-Sunrise.html
Saint-R�my, September, 1889, Reaper (after Millet):
http://www.vangoghgallery.com/catalog/Painting/464/Reaper-%28after-Millet%29,-The.html
Saint-R�my, September, 1889, Reaper with sickle (after Millet):
http://www.vangoghgallery.com/catalog/Painting/463/Reaper-with-Sickle-%28after-Millet%29.html
Cheers,
Carl Fogel
Michael Press
"Bill Sornson" <so...@noyb.com> wrote:
What of it?
--
Michael Press
Bill Sornson
> In article <hemr91$2p4$1...@news.eternal-september.org>,
> "Bill Sornson" <so...@noyb.com> wrote:
>
>> Michael Press wrote:
>>> In article
>>> <47f439ec-8dd9-4b02...@y28g2000prd.googlegroups.com>,
>>> datakoll <data...@yahoo.com> wrote:
>>>
>>>> PLANNING A TRIP ?
>>>>
>>>> noaa weather service
>>>>
>>>> and
>>>>
>>>> http://...
>>>
>>> What are you talking about?
>>
>> You ended a sentence with a preposition.
>
> What of it?
Pedants should know better.
datakoll
Saint-Rémy: September, 1889
Museum Folkwang
Essen, Germany, Europe
F: 619, JH: 1792
GETs INTO the idea. Amazing how talent brings French primitive up
several notches into Southby's.
'WIND' attempts an objective approach to a very subjective
experience. I am amazed at F1.
take a look at kayak/canoe/river running /white water as EDDY for
ideas in using windbreaks to advantage.
Michael Press
"Bill Sornson" <so...@noyb.com> wrote:
> Michael Press wrote:
> > In article <hemr91$2p4$1...@news.eternal-september.org>,
> > "Bill Sornson" <so...@noyb.com> wrote:
> >
> >> Michael Press wrote:
> >>> In article
> >>> <47f439ec-8dd9-4b02...@y28g2000prd.googlegroups.com>,
> >>> datakoll <data...@yahoo.com> wrote:
> >>>
> >>>> PLANNING A TRIP ?
> >>>>
> >>>> noaa weather service
> >>>>
> >>>> and
> >>>>
> >>>> http://...
> >>>
> >>> What are you talking about?
> >>
> >> You ended a sentence with a preposition.
> >
> > What of it?
>
> Pedants should know better.
Know what better than what?
--
Michael Press
Bill Sornson
> In article <4b10...@news.x-privat.org>,
> "Bill Sornson" <so...@noyb.com> wrote:
>
>> Michael Press wrote:
>>> In article <hemr91$2p4$1...@news.eternal-september.org>,
>>> "Bill Sornson" <so...@noyb.com> wrote:
>>>
>>>> Michael Press wrote:
>>>>> In article
>>>>> <47f439ec-8dd9-4b02...@y28g2000prd.googlegroups.com>,
>>>>> datakoll <data...@yahoo.com> wrote:
>>>>>
>>>>>> PLANNING A TRIP ?
>>>>>>
>>>>>> noaa weather service
>>>>>>
>>>>>> and
>>>>>>
>>>>>> http://...
>>>>>
>>>>> What are you talking about?
>>>>
>>>> You ended a sentence with a preposition.
>>>
>>> What of it?
>>
>> Pedants should know better.
>
> Know what better than what?
Than to end sentences with prepositions.
datakoll
spike costs $8
paint $30
camera $310
laptop $2100
site $40/day
bike $1400 with spares
van 29000 deluxe prob $37000 counting labor
CHEAP !!
reads like a government program
shall I send a canah CRC ?
datakoll
Michael Press
Where ever did you get such a notion?
--
Michael Press
Bill Sornson
> In article <4b10...@news.x-privat.org>,
> "Bill Sornson" <so...@noyb.com> wrote:
>
>> Michael Press wrote:
>>> In article <4b10...@news.x-privat.org>,
>>> "Bill Sornson" <so...@noyb.com> wrote:
>>>
>>>> Michael Press wrote:
>>>>> In article <hemr91$2p4$1...@news.eternal-september.org>,
>>>>> "Bill Sornson" <so...@noyb.com> wrote:
>>>>>
>>>>>> Michael Press wrote:
>>>>>>> In article
>>>>>>> <47f439ec-8dd9-4b02...@y28g2000prd.googlegroups.com>,
>>>>>>> datakoll <data...@yahoo.com> wrote:
>>>>>>>
>>>>>>>> PLANNING A TRIP ?
>>>>>>>>
>>>>>>>> noaa weather service
>>>>>>>>
>>>>>>>> and
>>>>>>>>
>>>>>>>> http://...
>>>>>>>
>>>>>>> What are you talking about?
>>>>>>
>>>>>> You ended a sentence with a preposition.
>>>>>
>>>>> What of it?
>>>>
>>>> Pedants should know better.
>>>
>>> Know what better than what?
>>
>> Than to end sentences with prepositions.
>
>
> Where ever did you get such a notion?
Wherever is one word.
Michael Press
Yes it is. "Where ever" is two words.
Now that we are done with the mathematical
portion of the thread, where ever did you
get such a notion?
--
Michael Press
Bill Sornson
I'll tell you when you stop nitpicking people's posts and using stilted,
convoluted language to appear superior. And again, the word is, "wherever".
HTH!
TomP
> RIDING IN THE WIND
>
> Wind is the bicyclists greatest and invisible adversary, however,
> being invisible doesn't mean it should remain a mystery.
> If performance is not an issue, the power of relative headwinds
> suggests not to fight them and be miserable, but rather to relax and
> exert effort when the route changes direction and the winds are more
> favorable.
Which is why 90+ cadence is a good rule to observe for most
recreational cyclists.
--
Tp,
-------- __o
----- -\<. -------- __o
--- ( )/ ( ) ---- -\<.
-------------------- ( )/ ( )
-----------------------------------------
No Lawsuit Ever Fixed A Moron...
Simon Lewis
> Jobst Brandt wrote:
>
>> RIDING IN THE WIND
>>
>> Wind is the bicyclists greatest and invisible adversary, however,
>> being invisible doesn't mean it should remain a mystery.
>
>> If performance is not an issue, the power of relative headwinds
>> suggests not to fight them and be miserable, but rather to relax and
>> exert effort when the route changes direction and the winds are more
>> favorable.
>
> Which is why 90+ cadence is a good rule to observe for most
> recreational cyclists.
Would you like to explain "why" there is any link whatsoever to such a
contentious subject as 90+ cadence.
andre...@aol.com
> On Nov 23, 1:24 pm, Jobst Brandt <jbra...@sonic.net> wrote:
>
>
>
>
>
> > Andy Coggan wrote:
> > >> It might appear that side winds create more or less drag than direct
> > >> headwinds or tailwinds as a result of a different rider and bicycle
> > >> profile that determines a drag coefficient. Practically the
> > >> aerodynamic profile is the same from any direction Because all parts
> > >> of the rider, including arms, legs, torso and head, as well as all
> > >> major bicycle parts, are round. Using a round model called a bluff
> > >> body to compute drag power from any wind directions was verified in
> > >> the wind tunnel (Fig 2), and has been used for these calculations.
> > > The "bluff body" assumption is a gross oversimplification.
>
> > I think deciphering what is meant by bluff body is important in this
> > discussion. A bluff body (the rider and his bicycle) are essentially
> > round cross sections who's drag is governed more by cross sectional
> > shape rather than orientation to the wind, having no airfoil tear-drop
> > streamlining. Therefore, the bluff body has similar drag in all
> > directions (in line-, cross-, and tailwinds.)
>
> ...which is not true for many cyclists.
>
> Andy Coggan
Hey, since you appeared here, I thought I ask this questions. How many
grms of carb per hour is it ok to consume not to bonk in long moderate
effort cycling (above aerobic range)? I do about 35 to 40 grms of
carb in gummy bears= to 2 gels. I weigh about 195. What is you view on
gummy bears or other cheap candy instead of the way more expensive
gels?
Thx
Andres
Michael Press
"Bill Sornson" <so...@noyb.com> wrote:
You start a conversation about prepositions,
then do not make a point.
--
Michael Press
Bill Sornson
What ever. (Get that point? Didn't think so.)
I'll type this slowly and then I'm done. You nitpick posts for minor errors
like grammar or incorrect word usage fairly often. Also, you do it in a
smug, condescending way more often than not. Finally, you seldom use
simple, declarative sentences to express your pedantic disdain of others;
rather, you choose stilted, convoluted verbiage (like "stream of people
populated by individuals") to appear superior to your poor rube victims.
Since you've assumed the role of Resident Pedant of RBT, I find your
numerous, frequent errors ironically entertaining.
Bill "that's about which I'm talking" S.
datakoll
gummy what ? poison...
Mars Bars / 3 Musketears !
interesting abt the bars. In condition and into the wind, sugar
effects are unnormal, no slacking musculature I'm aware of...
add rotini in raspberry yogurt kept cool in thermos.
but hold the $650 GPS puhlease ! yawl read that ? WTH is comin down
there ?
gummy bears
euphimism ?
thirty-six
Not a patch on a baked potato and cheese.
Norman
Dried figs are pretty cheap & don't turn into low-
quality tubular glue in hot weather. & since I'm
no racer (& can therefore stop without feeling
a need for penance) apple, pear, peach, or
apricot pie with aye scoupe of ice cream is
what I try to aim for.
For pure efficiency in terms of mass & energy,
CheezWiz is pretty hard to beat. Also provides
ofsetting FOD for those frame-pump wielding
Italians.
thirty-six
Applles or bananas are one of the best high sugar foods when riding
hard when one only needs the sugar. For best results when you may not
be able to feed properly because of racing pressure you need to
prepare the fruit by slicing it and coating it with a sugar glaze. My
attempts at it were messy it may be simpler to coat the fruit with
powdered sugar and pass a blowtorch quickly over them.
andre...@aol.com
gummy bears don't get gluey in hot weather. In El Paso Summers you
always end up riding above 90. Gummy bears are easy to eat and because
they are straight sugar with a little gelatin you need only a small
amount to get lots of carbs. The reason I like them is because they
are way cheaper than gels, they have essentially the same nutrition,
and taste better. Finally, lots of gels work into my teeth and give me
tooth aches. For a long ride, I'd need to carry several bananas or a
handful of gummies.
thirty-six
Ah, we have Tavener's Jelly Babies which are really soft and too easy
to eat, quite fruity as well in comparison to the stiffer big brand.
Michael Press
Bait and switch. jim beam runs that.
Let's talk about sentences ending with prepositions.
--
Michael Press
TomP
> TomP <roa...@socal.rr.com> writes:
>
> > Jobst Brandt wrote:
> >
> >> RIDING IN THE WIND
> >>
> >> Wind is the bicyclists greatest and invisible adversary, however,
> >> being invisible doesn't mean it should remain a mystery.
> >
> >> If performance is not an issue, the power of relative headwinds
> >> suggests not to fight them and be miserable, but rather to relax and
> >> exert effort when the route changes direction and the winds are more
> >> favorable.
> >
> > Which is why 90+ cadence is a good rule to observe for most
> > recreational cyclists.
>
> Would you like to explain "why" there is any link whatsoever to such a
> contentious subject as 90+ cadence.
Comfort.
thirty-six
> Simon Lewis wrote:
> > Would you like to explain "why" there is any link whatsoever to such a
> > contentious subject as 90+ cadence.
>
> Comfort.
Higher cadence is the result of choosing easier gears with less pedal
force.
Jobst Brandt
>>> Would you like to explain "why" there is any link whatsoever to such a
>>> contentious subject as 90+ cadence.
>> Comfort.
> Higher cadence is the result of choosing easier gears with less
> pedal force.
It seems you are unaware of riding speed being limited by aerobic
power, which doesn't change significantly over a range of cadences
(gears) for riders whose muscles are well exercised.
Jobst Brandt