OK - apparently that thread was too controversial. Let's try again...

[Tom]

This thread was Dunbarred when I tried to start it so let's do it once more.

Rider A heads up a level road directly into a headwind of X mph. Rider A averages Y mph. Rider A, before reaching the point of fatigue, turns around 180 degrees and heads home. Why does rider A not average X+Y mph on the way home, despite feeling that they are exerting as much effort?

For example, this afternoon I plan on riding about 15 miles west into a 30 mph headwind. I expect I'll average about 10 miles an hour. I'll turn around and head home, but I know I won't be going 40 miles an hour all the way back. Why?

[brians647]

This thread was Dunbarred when I tried to start it so let's do it once more.

Rider A heads up a level road directly into a headwind of X mph. Rider A averages Y mph. Rider A, before reaching the point of fatigue, turns around 180 degrees and heads home. Why does rider A not average X+Y mph on the way home, despite feeling that they are exerting as much effort?

For example, this afternoon I plan on riding about 15 miles west into a 30 mph headwind. I expect I'll average about 10 miles an hour. I'll turn around and head home, but I know I won't be going 40 miles an hour all the way back. Why?

I know I'm missing some explanations, but I have three:

1) drivetrain/tire friction energy losses (very minor)
2) aerodynamic resistance is exponential (I believe) (*wait, does that even play a role here? no, still sleepy)
3) as I've learned with my power meter, it's easier to develop power up hills/into wind as you can keep more pressure on the pedals. When going slightly downhill at a higher speed or with a tailwind, making the same wattage is much more difficult.

Okay, I'm missing a couple obvious ones I'm sure, but I'm not a guru, and I haven't even had my coffee yet!

[BumbleBeeDave]

This thread was Dunbarred when I tried to start it so let's do it once more.

Rider A heads up a level road directly into a headwind of X mph. Rider A averages Y mph. Rider A, before reaching the point of fatigue, turns around 180 degrees and heads home. Why does rider A not average X+Y mph on the way home, despite feeling that they are exerting as much effort?

For example, this afternoon I plan on riding about 15 miles west into a 30 mph headwind. I expect I'll average about 10 miles an hour. I'll turn around and head home, but I know I won't be going 40 miles an hour all the way back. Why?

Where's the Moderator? :D ;)

BBD

[mflaherty37]

The answers lie within the road load equation..

http://www.collaboratory.ucr.edu/publications/Diesel_Vehicle_Fuel_Consumption.pdf

[Big Daddy]

what color was it?

[Tom]

what color was it?

The road? It's grey, like all the roads.

Oh... you mean the bike. That's it. The bike's grey, too.

[jasond]

[QUOTE=brians647]
3) as I've learned with my power meter, it's easier to develop power up hills/into wind as you can keep more pressure on the pedals. When going slightly downhill at a higher speed or with a tailwind, making the same wattage is much more difficult.QUOTE]

+1....I experienced this yesterday. I had a 13mph tailwind yesterday and had a tough time keeping pressure on the pedals. Were as when I had a headwind I was able to keep pressure on the pedals constantly. I probably averaged 13ish with a headwind and well into the 20's with a tailwind.

J

[Too Tall]

Analytic Cycling 101. Resistance is futile.

[Lifelover]

....
2) aerodynamic resistance is exponential (I believe) (*wait, does that even play a role here? no, still sleepy)



I think that is THE major part of it.

[Kevan]

on your way back you're too tired from the effort going out.

[M.Sommers]

This thread was Dunbarred when I tried to start it so let's do it once more.

Rider A heads up a level road directly into a headwind of X mph. Rider A averages Y mph. Rider A, before reaching the point of fatigue, turns around 180 degrees and heads home. Why does rider A not average X+Y mph on the way home, despite feeling that they are exerting as much effort?

For example, this afternoon I plan on riding about 15 miles west into a 30 mph headwind. I expect I'll average about 10 miles an hour. I'll turn around and head home, but I know I won't be going 40 miles an hour all the way back. Why?

1). An object at rest tends to stay at rest and an object in motion, stays in motion, with the same speed and direction, unless impacted by an unbalanced force. Sir Newton.

2). Mental effect/affect. Golf. Ever get to the tee box and the wind is in your face? Happens all the time atmo, and when it does, the golfer 'thinks' he must kill the ball, tries to, overswings and hits a horrible shot. In golf, the law is 'hit the ball purely, square and the wind, even a strong one, will have little effect.' Sir Tom Watson has many quotes/ideas on the subject, they evolved after his win at The Open (aka The British Open) and Watson always enjoyed a huge wind at a key round of a tournament (like Turnberry, where he mastered Newton's law and knew his competition did not).

3). When I ride into the wind I remind myself of the Rule from golf; I try to ride with perfect form and it diminishes the impact of the wind. I also ride in the drops bigtime. I lastly think of Christopher Cross' big hit, 'Ride Like the Wind'.

[Tom]

1). An object at rest tends to stay at rest and an object in motion, stays in motion, with the same speed and direction, unless impacted by an unbalanced force. Sir Newton.

3). ... I lastly think of Christopher Cross' big hit, 'Ride Like the Wind'.

Unbalanced does describe me well.

I, personally, think of 'Call Me the Breeze'. JJ Cale.

[goonster]

Turbulent flow.

To impede you, the wind need only swirl randomly around you. To assist you it must push you along smoothly from precisely the right direction.

The perfect tailwind is the one going exactly as fast as you are.

[DRZRM]

Think about yourself as a sail. Because you are round (no offense) and thus aerodynamic to some extent, the wind does not impact you all that much. If you leave out all the other frictions on the bike, if you were perfectly non-aero and worked like a sail, it would be impossible for you to ride into a 30 mph headwind at all, unless you could average >30 mph without wind. As you know, that is not the case (though it might be impossible for me to ride into a 30 mph headwind without falling over, it's been a long winter). The same principle works in reverse, you benefit from the wind (that's why you go faster once you turn) but not perfectly because most of that energy slips around you.

I hope that helps answer your question, that's what you get talking physics with a historian (for what it's worth, I declared a physics major in college for a year before I realized that I was just too stupid, and got a PhD in history).

[DRZRM]

Yeah, that's what I meant...I think.

Turbulent flow.

To impede you, the wind need only swirl randomly around you. To assist you it must push you along smoothly from precisely the right direction.

The perfect tailwind is the one going exactly as fast as you are.

[idig]

African or European?

[RPS]

For example, this afternoon I plan on riding about 15 miles west into a 30 mph headwind. I expect I'll average about 10 miles an hour. I'll turn around and head home, but I know I won't be going 40 miles an hour all the way back. Why?You know this because you've done it before? :rolleyes:

Tom, did you get the answer you were looking for, or was the question meant as a joke (or brain teaser)?

[Fivethumbs]

The same question would be "If I sit on my bike and a 30 mph wind comes up, will it push me at 30 mph if I don't pedal?" The answer would be no. Why? Gravity.
















'

[RPS]

The same question would be "If I sit on my bike and a 30 mph wind comes up, will it push me at 30 mph if I don't pedal?" The answer would be no. Why? Gravity.In technical schools they don't often ask questions with simple yes or no answers. It would be more like: given these XYZ conditions, if you sit up with a 30 MPH tail wind estimate how fast the wind will push you along. And I'd expect only one right answer. :beer:

[stevep]

cause you need a new bike.

[stevep]

1). An object at rest tends to stay at rest and an object in motion, stays in motion, with the same speed and direction, unless impacted by an unbalanced force. Sir Newton.
.

nap time.
this object is going to take a rest and stay at rest for an hour.

[Tom]

Turbulence thing. I wondered why I cared about a crosswind. Now I know.

[Blue Jays]

"...To impede you, the wind need only swirl randomly around you. To assist you it must push you along smoothly from precisely the right direction. The perfect tailwind is the one going exactly as fast as you are..."Exactly correct. To state in a different way, a headwind can be virtually any offset breeze that slows progress. It doesn't need to be a square-on "headwind" to require an increase in pedaling force.
For a tailwind to be successful, it has to be almost perfectly aligned with a rider's back to truly boost speed.

[RPS]

For a tailwind to be successful, it has to be almost perfectly aligned with a rider's back to truly boost speed. :confused: :confused:
:confused: :confused:

Care to explain why you think this?
But first define "almost perfectly aligned".

[RocketDog]

I can't sort through what is meant by some of the responses here; I also can't state the answer to the OP's question better than Jobst:

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

[Elefantino]

on your way back you're too tired from the effort going out.
POTD!