Drafting effects for highway riding

On Sat, 27 Aug 2005 06:46:14 GMT, [email hidden]

(Stuart Lynne) said:

One of my favourite training rides is out on a rolling sub-urban highway
that has wide shoulders.

I have noticed that my average speed seems higher on this route than
some others I do and the only difference I can think of is that perhaps
there are some drafting effects from the automotive traffic.

I'm not attempting to draft, I'm in my own lane (or shoulder). But there
is a fairly continous amount of traffic passing by at about 80Kmh
(50Mph) and I find my average speed is about 5-10Kmh higher than I would
normally do (on other rides with less traffic..)

Has anyone quantified this? It certainly does not appear to be as good
as following another cyclist, but it does appear to be helpful..

Or am I just imagining things, it could be just the extra adrenalin from
the cars zipping by ...

Dear Stuart,

It's not your imagination, but it's going to be awfully hard
to quantify, since the vehicles zipping past you vary so
much in shape and size, distance from your lane, and number
per minute.

But you can get some idea of the turbulence involved and
which way it's going by watching a car idle down a quiet,
leaf-covered street on a windless day.

At 20 mph, the car's invisible wake will swirl up leaves to
either side, which keep swirling and follow the car for some
time after it's passed.

Or you can just ride out a lonelier highway as I do, and
note the wind blast as a car goes by. You can feel the gust
buffeting you when a car goes past the other way in the
opposite lane, so an even stronger gust is helping you when
an overtaking car zips past much closer--it's just that
you're going in the same direction, so the helpful tailwind
is harder to feel.

Carl Fogel

Stuart Lynne said:

One of my favourite training rides is out on a rolling sub-urban highway
that has wide shoulders.

I have noticed that my average speed seems higher on this route than
some others I do and the only difference I can think of is that perhaps
there are some drafting effects from the automotive traffic.

I'm not attempting to draft, I'm in my own lane (or shoulder). But there
is a fairly continous amount of traffic passing by at about 80Kmh
(50Mph) and I find my average speed is about 5-10Kmh higher than I would
normally do (on other rides with less traffic..)

Has anyone quantified this? It certainly does not appear to be as good
as following another cyclist, but it does appear to be helpful..

Or am I just imagining things, it could be just the extra adrenalin from
the cars zipping by ...

There is a stretch along my regular loop where I run parallel to, and
slightly above a freeway. The traffic moves counter to my direction.
I've noted that there is always a headwind along there. It isn't a huge
headwind, but it's noticable. I too figured it must be something I
imagined, but my daughter noted it too. My horizontal distance is about
100 m and I'm roughly 15 m above the freeway traffic.

I doubt you can quantify this for the reasons given by another poster.

-paul

the vehicles create a tunnel of wind debris exhaust gases carbon rubber
particles all charged and somewhat cohesive
the drafting sweet spot can be about five car lengths back-there a
crest in there like surf-find it and roll
UPS trucks in convoy down the intercoastal bridge are a trip

Quoted message said:

the vehicles create a tunnel of wind debris exhaust gases carbon rubber
particles all charged and somewhat cohesive
the drafting sweet spot can be about five car lengths back-there a
crest in there like surf-find it and roll
UPS trucks in convoy down the intercoastal bridge are a trip

City buses work well - 30 mph speeds at a 15 mph effort. Fat tires are a
good idea, since you won't see the potholes in time to avoid them.

--
Sniper Anon

----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
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Stuart Lynne said:

One of my favourite training rides is out on a rolling sub-urban
highway that has wide shoulders.

I have noticed that my average speed seems higher on this route than
some others I do and the only difference I can think of is that
perhaps there are some drafting effects from the automotive traffic.

I'm not attempting to draft, I'm in my own lane (or shoulder). But
there is a fairly continous amount of traffic passing by at about
80Kmh (50Mph) and I find my average speed is about 5-10Kmh higher
than I would normally do (on other rides with less traffic..)

Has anyone quantified this? It certainly does not appear to be as good
as following another cyclist, but it does appear to be helpful..

Or am I just imagining things, it could be just the extra adrenalin
from the cars zipping by ...

Ask brit time trialists.

--
Andy Morris

AndyAtJinkasDotFreeserve.Co.UK

Love this:
Put an end to Outlook Express's messy quotes
http://home.in.tum.de/~jain/software/oe-quotefix/

Sniper Anon said:

Quoted message said:

the vehicles create a tunnel of wind debris exhaust gases carbon
rubber particles all charged and somewhat cohesive
the drafting sweet spot can be about five car lengths back-there a
crest in there like surf-find it and roll
UPS trucks in convoy down the intercoastal bridge are a trip

City buses work well - 30 mph speeds at a 15 mph effort. Fat tires
are a good idea, since you won't see the potholes in time to avoid
them.

Bill Baka lives!

Sniper Anon said:

City buses work well - 30 mph speeds at a 15 mph effort. Fat tires are a
good idea, since you won't see the potholes in time to avoid them.

City buses are a problem as they tend to pull over
and stop every few blocks. The best vehicle to draft
is an ambulance with sirens blaring.

Robert

Paul Cassel said:

Stuart Lynne said:

One of my favourite training rides is out on a rolling sub-urban highway
that has wide shoulders.

I have noticed that my average speed seems higher on this route than
some others I do and the only difference I can think of is that perhaps
there are some drafting effects from the automotive traffic.

I'm not attempting to draft, I'm in my own lane (or shoulder). But there
is a fairly continous amount of traffic passing by at about 80Kmh
(50Mph) and I find my average speed is about 5-10Kmh higher than I would
normally do (on other rides with less traffic..)

Has anyone quantified this? It certainly does not appear to be as good
as following another cyclist, but it does appear to be helpful..

Or am I just imagining things, it could be just the extra adrenalin from
the cars zipping by ...

There is a stretch along my regular loop where I run parallel to, and
slightly above a freeway. The traffic moves counter to my direction.
I've noted that there is always a headwind along there. It isn't a huge
headwind, but it's noticable. I too figured it must be something I
imagined, but my daughter noted it too. My horizontal distance is about
100 m and I'm roughly 15 m above the freeway traffic.

I doubt you can quantify this for the reasons given by another poster.

-paul

Dear Paul,

Possibly the "100 m" is a typo for "10 m"?

Given vehicles of ordinary size and speed, it's unlikely
that the turbulence of their passage can be detected, much
less affect a bicycle, at 100 meters in open air.

Open air works well for transmitting sound by compression
waves, but poorly for actual flow--the friction of the 400
feet of intervening air damps the turbulence noticed up
close when the 5-foot-high cars and 12-foot-high trucks zip
by.

You can test this by blowing at a kleenex tucked into the
pages of a book a few feet away--the kleenex will move.

Now take another kleenex, hold it in your hand, and bring it
in from the side as you imitate a bellows.

Notice how close the kleenex in your hand can come to the
air blast that shakes the kleenex hanging out of the
book--the stream of turbulence doesn't have much side
effect.

This is why geese must fly so close to each other when
they're taking advantage of the turbulence swirling off the
wing tip of the goose ahead and to one side--the turbulence
rapidly dissipates.

The same problem was what made flying heavy daylight bombers
so physically hard--tactical theory dictated a formation
tight enough that the trailing bomber pilots fought the
controls for hours as their planes were buffeted by the
turbulence of the bombers ahead of them. Easing off fifty
feet made a huge difference--the plane became much easier
to fly.

In any case, assuming that you're talking about a two-way
freeway, there would be traffic heading in the other
direction within 110 meters or so. At typical freeway
traffic levels, this would tend to cancel out a good deal of
any effect.

I suspect that you're either much closer than 100 meters to
the freeway (10 meters is getting plausible), or that you're
just riding into a prevailing wind, which can be easily
magnified by a 15 meter bank.

Carl Fogel

In article <[email hidden]>,
[email hidden] says...

Quoted message said:

Or you can just ride out a lonelier highway as I do, and
note the wind blast as a car goes by. You can feel the gust
buffeting you when a car goes past the other way in the
opposite lane, so an even stronger gust is helping you when
an overtaking car zips past much closer--it's just that
you're going in the same direction, so the helpful tailwind
is harder to feel.

and the vortex is blown sideways by any crosswind component which makes
the big difference.

the four trailer road-trains we have here demonstrate these effects quite
well.

Bruce G

-City buses work well - 30 mph speeds at a 15 mph effort. Fat tires are
a
-good idea, since you won't see the potholes in time to avoid them.

On a good semi-rural road where I used to live, I could easily hit
40MPH behind a (CNG powered) city bus. I wouldn't try this on a diesel
one, though.

I remember seeing something a few years ago on one of those popular
science type tv shows where people were trying to put very small wind
electric generators along a NJ highway. It had those very high walls
and created quite a breeze.

Quoted message said:

On Sat, 27 Aug 2005 10:12:59 -0600, Paul Cassel

Quoted message said:

Dear Paul,

Possibly the "100 m" is a typo for "10 m"?

Given vehicles of ordinary size and speed, it's unlikely
that the turbulence of their passage can be detected, much
less affect a bicycle, at 100 meters in open air.

Open air works well for transmitting sound by compression
waves, but poorly for actual flow--the friction of the 400
feet of intervening air damps the turbulence noticed up
close when the 5-foot-high cars and 12-foot-high trucks zip
by.

You can test this by blowing at a kleenex tucked into the
pages of a book a few feet away--the kleenex will move.

Now take another kleenex, hold it in your hand, and bring it
in from the side as you imitate a bellows.

Notice how close the kleenex in your hand can come to the
air blast that shakes the kleenex hanging out of the
book--the stream of turbulence doesn't have much side
effect.

This is why geese must fly so close to each other when
they're taking advantage of the turbulence swirling off the
wing tip of the goose ahead and to one side--the turbulence
rapidly dissipates.

The same problem was what made flying heavy daylight bombers
so physically hard--tactical theory dictated a formation
tight enough that the trailing bomber pilots fought the
controls for hours as their planes were buffeted by the
turbulence of the bombers ahead of them. Easing off fifty
feet made a huge difference--the plane became much easier
to fly.

In any case, assuming that you're talking about a two-way
freeway, there would be traffic heading in the other
direction within 110 meters or so. At typical freeway
traffic levels, this would tend to cancel out a good deal of
any effect.

I suspect that you're either much closer than 100 meters to
the freeway (10 meters is getting plausible), or that you're
just riding into a prevailing wind, which can be easily
magnified by a 15 meter bank.

Carl,

It wasn't a typo, but was a serious wrong estimate of the distance. I
went that route again today and as you state, the distance is much
closer than I stated above. There is also a flyover which is closer yet
and also comes from higher than the bike path and closer than the
freeway which may have some effect.

Today that stretch had a clear tailwind if no other factors intruded,
but, true to form, the wind there was neutral due to whatever micro
weather is prevalent at that locale. That too may be a factor we can't
ignore. That section is a huge freeway intersection (largest in the
state by far) which creates a somewhat porous wall of concrete where the
porosity are the bridges where the cars go. That may create a mini
weather pattern which would result in a headwind even if no cars were
present.

I think that may be a contributor because I haven't noted a significant
difference in the effect linked to traffic volume. I've been by there at
0530 during the long days when there isn't much traffic, but noted the
headwind (or tailwind if going the other way).

-paul

Stuart Lynne said:

I have noticed that my average speed seems higher on this route than
some others I do and the only difference I can think of is that perhaps
there are some drafting effects from the automotive traffic.

If you want to see this stuff illuminated, get a copy
of _An Album of Fluid Motion_ by Van Dyke.

http://www.amazon.com/exec/obidos/tg/detail/-/0915760029/103-5663916-3258233

--Blair
"Then imagine yourself a particle
in a viscous substance..."

Blair P. Houghton said:

Stuart Lynne said:

I have noticed that my average speed seems higher on this route than
some others I do and the only difference I can think of is that
perhaps there are some drafting effects from the automotive traffic.

Quoted message said:

If you want to see this stuff illuminated, get a copy
of _An Album of Fluid Motion_ by Van Dyke.

He /was/ a pretty good tap dancer in his day.

[censored] Humor Bill (slow night)