aerodynamics question re drafting

Since drag increases exponentially with speed a good example to look
at would be Nascar races where they are at 180mph.

A group of cars goes faster than a single car - does that filter down
to bikes?

I know Robbie McEwen likes to try bump drafting.

Quoted message said:

i never thought that drafting a leader slowed them down a bit. but i've
heard several people comment on this effect. prehaps refering to a
disruption of airflow around the front cyclist. and apparently lance
refers to this effect in one sentence of his book, but it might be
miswritten or misconstrued.
any aerodynamic wizards out there with an answer? does drafting
someone slow the front rider down at all?
thanks

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

Quoted message said:

i never thought that drafting a leader slowed them down a bit. but i've
heard several people comment on this effect.

Then you heard stupid people. The front guy burns more energy but it doesn't
come from the rear guys. If anything, and the effect must be so slight as to
be indetectable, the guy behind actually fills in the space behind and
improves the aerodynamics.

I think that someone once computed that the effect couldn't be measured
because the distance was to great in the appropriate speed regimes.

the blur said:

does drafting
someone slow the front rider down at all?

I've seen this topic come up before, and nobody has cited a study that
addressed this issue directly AFAIK. I thought with all the power
meters out there maybe someone would have done it by now... or, you
could even get a good idea doing coast down tests... I'll have to keep
that in mind.

In "Bicycling Science" they show some old wind tunnel data with
vertical cylinders drafting each other, and another with vertical
struts (aero shape). Drag on each is plotted vs relative distance
between. Keep in mind that neither shape approximates the shape of a
bike rider very well.

Drag on the forward cylinder is slightly reduced, with a minimum Cd
value at x/d = 2. This is a bit closer than bicyclists could get, I
think. By x/d = 3, Cd has jumped up to within a few percent of what the
cylinder would have if it was alone, and it slowly rises to it's "lone"
value at infinity. BTW, the drafting cylinder's drag is only a 3rd of
it's "lone" value.

With the aero struts, the lead strut gets a *huge* benefit at x/c = 1,
and the rear strut receives much *higher* drag. By x/c = 3 to infinity,
they are back to nearly equal drag but the rear strut is still slightly
higher.

So... I'd guess that having someone behind is very slightly beneficial
to the leader... wish they'd test actual bike riders, though.

Ron Ruff said:

the blur said:

does drafting someone slow the front rider down at all?

I've seen this topic come up before, and nobody has cited a study that
addressed this issue directly AFAIK. I thought with all the power
meters out there maybe someone would have done it by now... or, you
could even get a good idea doing coast down tests... I'll have to keep
that in mind.

This is at most a few percent effect. I think it would be very
difficult to get accurate enough results outdoors even with power
meters. You'd need a wind tunnel. Forget coast down tests -
people have difficulty getting repeatable results even to judge
reasonably large differences in aero drag of a solo rider.
1-2 mph difference in ambient wind is probably enough to throw
everything off.

Quoted message said:

In "Bicycling Science" they show some old wind tunnel data with
vertical cylinders drafting each other, and another with vertical
struts (aero shape). Drag on each is plotted vs relative distance
between. Keep in mind that neither shape approximates the shape of a
bike rider very well.

Drag on the forward cylinder is slightly reduced, with a minimum Cd
value at x/d = 2. This is a bit closer than bicyclists could get, I
think. By x/d = 3, Cd has jumped up to within a few percent of what the
cylinder would have if it was alone, and it slowly rises to it's "lone"
value at infinity. BTW, the drafting cylinder's drag is only a 3rd of
it's "lone" value.
With the aero struts, the lead strut gets a *huge* benefit at x/c = 1,
and the rear strut receives much *higher* drag. By x/c = 3 to infinity,
they are back to nearly equal drag but the rear strut is still slightly
higher.

So... I'd guess that having someone behind is very slightly beneficial
to the leader... wish they'd test actual bike riders, though.

For actual riders, drafting in a single paceline is estimated
to save about 30 percent of power. This can be measured with
power meters (was it done outdoors, in a wind tunnel? Coggan
probably knows).

Compare that to the 2/3rds savings for drafting cylinders and
the increase for aero struts. That probably tells you that
the cylinders were too close and that aero forms have much
too low drag to be a good approximation of a rider.

Wind tunnels big enough to hold riders, as opposed to cylinders,
are expensive.

If you ask the question outside of July when Chung and Coggan
are paying more attention you might get a better answer. Also,
for the OP, try googling in rec.bicycles.tech.

the blur said:

i never thought that drafting a leader slowed them down a bit. but i've
heard several people comment on this effect.

You mean physically/aerodynamically slow the leader down? Or
tactically/psychologically (the leader knows he will just be wasting
his energy pulling the other guy)?

Quoted message said:

Since drag increases exponentially with speed a good example to look
at would be Nascar races where they are at 180mph.

http://www.firstmonday.dk/issues/issue5_2/ronfeldt/index.html

JT

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the blur said:

does drafting someone slow the front rider down at all?

It didn't slow down Pereiro et al.

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[email hidden] a écrit :

Quoted message said:

Since drag increases exponentially with speed a good example to look
at would be Nascar races where they are at 180mph.

The correct term is: "increases exponentially like the square"
as used by Joe Friel in his book.

-ilan

the blur said:

i never thought that drafting a leader slowed them down a bit. but i've
heard several people comment on this effect. prehaps refering to a
disruption of airflow around the front cyclist. and apparently lance
refers to this effect in one sentence of his book, but it might be
miswritten or misconstrued.
any aerodynamic wizards out there with an answer? does drafting
someone slow the front rider down at all?
thanks

actually- the front rider receives a small aerodynamic _benefit_ from
the trailing cyclists.

this effect is descibed for stock cars in movie Days of Thunder- Robert
Duval's character explains that 2 cars traveling together can share the
effort of breaking the wind and go faster than a single car.

the trailing vehicle keeps the airflow from being disrupted behind the
vehicle, making an improved slipstream.

I have a book at home- Olympic book on endurance or something- that says
that this same effect applies to cyclists in a paceline.

they have a chart with drafting benefit to each rider depending on pack
size and claim a benefit for the leading rider. the effect was
obviously much smaller than what trailing riders get, but not
insignificant- on the order of a few percent.

marc

Marc said:

the blur said:

i never thought that drafting a leader slowed them down a bit. but i've
heard several people comment on this effect. prehaps refering to a
disruption of airflow around the front cyclist. and apparently lance
refers to this effect in one sentence of his book, but it might be
miswritten or misconstrued. any aerodynamic wizards out there with an
answer? does drafting
someone slow the front rider down at all?
thanks

here's 3 expert responses- definitely no disadvantage from being the
draftee- getting a true advantage is possible but not definitive...

-marc

http://www.insidetri.com/train/bike/articles/1311.0.html

Answer from aerodynamics professor and Project 96 and 1984 U.S. Olympic
Team bike designer, Dr. Chester Kyle:
We measured this in the General Motors Wind Tunnel in 1996, and on the
track using the SRM crank dynamometers. The lead rider in a 4-man pace
line uses about 2 to 3 percent less energy than they would if riding solo.

The next in line needs about 71 percent of the lead rider's power, and
the third and fourth riders about 65 percent. See "Racing cyclist power
requirements in the 4000-m individual and team pursuits", Medicine and
Science in Sports and Exercise, v31, no.11, pp 1677-1685, 1999. J.P.
Broker, C.R. Kyle and E.R. Burke.
--Chet Kyle

Answer from aerodynamics guru and advisor to the U.S. Postal team, John
Cobb:
About two days after this question I was going to the wind tunnel
already to do some testing so I took a few minutes to set up this test.
I couldn't find that the rear bike had any affect on the front bike in
any wind angle. I tried a disc wheel and a standard wheel on the lead
bike. I don't think bicycles go fast enough for the air compression that
cars get to happen on bikes. When the bike is drafting it's drag was cut
virtually in half out to 10 degrees and was about 60 percent when set up
as an echelon out to 30 degrees.
-- John Cobb

Answer from chief wheel builder at Hed Design:
Theoretically you should get some benefit from the rider behind because
he would reduce the turbulence of the air coming off you. But in
practice you would have to go really fast, maybe 200 mph to make it
measurable. I think it works for something like stock car racing, but
they are bigger, faster, and probably more aero to start with.
--Andy
Hed Design

[email hidden] a écrit :

Quoted message said:

Quoted message said:

Since drag increases exponentially with speed a good example to look
at would be Nascar races where they are at 180mph.

ilanpi said:

The correct term is: "increases exponentially like the square"
as used by Joe Friel in his book.

Wow, broken english and broken mathematics in one sentence. Such economy
of style.

I was told that the distance with single bikes (drafter can only get so
close with both wheels in the way) the one pulling is only nominally
affected by the one drafting. However, in the case of a tandem, that the
stoker is actually close enough to the captain to improve the aerodynamics
of the "whole".

?

ie
'ride fast, take chances'

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

Quoted message said:

Marc said:

the blur said:

i never thought that drafting a leader slowed them down a bit. but i've
heard several people comment on this effect. prehaps refering to a
disruption of airflow around the front cyclist. and apparently lance
refers to this effect in one sentence of his book, but it might be
miswritten or misconstrued. any aerodynamic wizards out there with an
answer? does drafting
someone slow the front rider down at all?
thanks

here's 3 expert responses- definitely no disadvantage from being the
draftee- getting a true advantage is possible but not definitive...

-marc

http://www.insidetri.com/train/bike/articles/1311.0.html

Answer from aerodynamics professor and Project 96 and 1984 U.S. Olympic
Team bike designer, Dr. Chester Kyle:
We measured this in the General Motors Wind Tunnel in 1996, and on the
track using the SRM crank dynamometers. The lead rider in a 4-man pace
line uses about 2 to 3 percent less energy than they would if riding solo.

The next in line needs about 71 percent of the lead rider's power, and the
third and fourth riders about 65 percent. See "Racing cyclist power
requirements in the 4000-m individual and team pursuits", Medicine and
Science in Sports and Exercise, v31, no.11, pp 1677-1685, 1999. J.P.
Broker, C.R. Kyle and E.R. Burke.
--Chet Kyle

Answer from aerodynamics guru and advisor to the U.S. Postal team, John
Cobb:
About two days after this question I was going to the wind tunnel already
to do some testing so I took a few minutes to set up this test. I couldn't
find that the rear bike had any affect on the front bike in any wind
angle. I tried a disc wheel and a standard wheel on the lead bike. I don't
think bicycles go fast enough for the air compression that cars get to
happen on bikes. When the bike is drafting it's drag was cut virtually in
half out to 10 degrees and was about 60 percent when set up as an echelon
out to 30 degrees.
-- John Cobb

Answer from chief wheel builder at Hed Design:
Theoretically you should get some benefit from the rider behind because he
would reduce the turbulence of the air coming off you. But in practice you
would have to go really fast, maybe 200 mph to make it measurable. I think
it works for something like stock car racing, but they are bigger, faster,
and probably more aero to start with.
--Andy
Hed Design

ie said:

I was told that the distance with single bikes (drafter can only get so
close with both wheels in the way) the one pulling is only nominally
affected by the one drafting.

What does "nominally" mean?

JT

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John Forrest Tomlinson said:

ie said:

I was told that the distance with single bikes (drafter can only get so
close with both wheels in the way) the one pulling is only nominally
affected by the one drafting.

What does "nominally" mean?

JT

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Main Entry: 1nom·i·nal
Pronunciation: 'nä-m&-n&l, 'näm-n&l
Function: adjective
Etymology: Middle English nominalle, from Medieval Latin nominalis,
from Latin, of a name, from nomin-, nomen name -- more at NAME
1 : of, relating to, or being a noun or a word or expression taking a
noun construction
2 a : of, relating to, or constituting a name b : bearing the name of
a person
3 a : existing or being something in name or form only <nominal head
of his party> b : of, being, or relating to a designated or
theoretical size that may vary from the actual : APPROXIMATE c :
TRIFLING, INSIGNIFICANT
4 of a rate of interest a : equal to the annual rate of simple
interest that would obtain if interest were not compounded when in
fact it is compounded and paid for periods of less than a year b :
equal to the percentage by which a repaid loan exceeds the principal
borrowed with no adjustment made for inflation
5 : being according to plan : SATISFACTORY <everything was nominal
during the spacecraft launch>
- nom·i·nal·ly adverb

David Ferguson said:

John Forrest Tomlinson said:

ie said:

I was told that the distance with single bikes (drafter can only get so
close with both wheels in the way) the one pulling is only nominally
affected by the one drafting.

What does "nominally" mean?

JT

Quoted message said:

Quoted message said:

****************************

Main Entry: 1nom·i·nal
Pronunciation: 'nä-m&-n&l, 'näm-n&l
Function: adjective
Etymology: Middle English nominalle, from Medieval Latin nominalis,
from Latin, of a name, from nomin-, nomen name -- more at NAME
1 : of, relating to, or being a noun or a word or expression taking a
noun construction
2 a : of, relating to, or constituting a name b : bearing the name of
a person
3 a : existing or being something in name or form only <nominal head
of his party> b : of, being, or relating to a designated or
theoretical size that may vary from the actual : APPROXIMATE c :
TRIFLING, INSIGNIFICANT
4 of a rate of interest a : equal to the annual rate of simple
interest that would obtain if interest were not compounded when in
fact it is compounded and paid for periods of less than a year b :
equal to the percentage by which a repaid loan exceeds the principal
borrowed with no adjustment made for inflation
5 : being according to plan : SATISFACTORY <everything was nominal
during the spacecraft launch>
- nom·i·nal·ly adverb

I'm sorry, I meant what does "nominally" mean in the sentence "I was
told that the distance with single bikes (drafter can only get so
close with both wheels in the way) the one pulling is only nominally
affected by the one drafting"?

JT

****************************
Remove "remove" to reply
Visit http://www.jt10000.com
****************************

John Forrest Tomlinson said:

Quoted message said:

Main Entry: 1nom·i·nal
Pronunciation: 'nä-m&-n&l, 'näm-n&l
Function: adjective
Etymology: Middle English nominalle, from Medieval Latin nominalis,
from Latin, of a name, from nomin-, nomen name -- more at NAME
1 : of, relating to, or being a noun or a word or expression taking a
noun construction
2 a : of, relating to, or constituting a name b : bearing the name of
a person
3 a : existing or being something in name or form only <nominal head
of his party> b : of, being, or relating to a designated or
theoretical size that may vary from the actual : APPROXIMATE c :
TRIFLING, INSIGNIFICANT
4 of a rate of interest a : equal to the annual rate of simple
interest that would obtain if interest were not compounded when in
fact it is compounded and paid for periods of less than a year b :
equal to the percentage by which a repaid loan exceeds the principal
borrowed with no adjustment made for inflation
5 : being according to plan : SATISFACTORY <everything was nominal
during the spacecraft launch>
- nom·i·nal·ly adverb

I'm sorry, I meant what does "nominally" mean in the sentence "I was
told that the distance with single bikes (drafter can only get so
close with both wheels in the way) the one pulling is only nominally
affected by the one drafting"?

3c.

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David Ferguson said:

Quoted message said:

Quoted message said:

Main Entry: 1nom·i·nal
3 a : existing or being something in name or form only <nominal head
of his party> b : of, being, or relating to a designated or
theoretical size that may vary from the actual : APPROXIMATE c :
TRIFLING, INSIGNIFICANT
- nom·i·nal·ly adverb

John Forrest Tomlinson said:

Quoted message said:

I'm sorry, I meant what does "nominally" mean in the sentence "I was
told that the distance with single bikes (drafter can only get so
close with both wheels in the way) the one pulling is only nominally
affected by the one drafting"?

Ewoud Dronkert said:

3c.

Nominated for shortest ever rbr post.

it means "a little bit".

Marc said:

here's 3 expert responses- definitely no disadvantage from being the
draftee- getting a true advantage is possible but not definitive...

-marc

http://www.insidetri.com/train/bike/articles/1311.0.html

Answer from aerodynamics professor and Project 96 and 1984 U.S. Olympic
Team bike designer, Dr. Chester Kyle:
We measured this in the General Motors Wind Tunnel in 1996, and on the
track using the SRM crank dynamometers. The lead rider in a 4-man pace
line uses about 2 to 3 percent less energy than they would if riding solo.

The team is going approx 60 kph and the following riders have about 4-7
cm between the rear wheel of the rider ahead and their own front wheel.
That makes a difference.