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Calculating windchill...

Old 01-17-20, 09:33 AM
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Calculating windchill...

If the temperature is 21F and I'm cycling at 12mph into a 24mph headwind, is the windchill calculated using 36mph?

Similarly, if I'm traveling at 24mph with a 24mph tailwind is windchill negated?
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Old 01-17-20, 12:36 PM
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my guesses

yes, 21 - 36 = -15 degrees

yes

winter is coming back to my area Brrrr!
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Old 01-17-20, 03:48 PM
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Originally Posted by rumrunn6 View Post
my guesses

yes, 21 - 36 = -15 degrees
You can't subtract windspeed from temperature, can you?
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Old 01-17-20, 03:55 PM
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Windchill and cycling ...

(Initially, I posted this query in the winter cycling sub-forum. But this sub-forum seems to get a lot more traffic)

If the temperature is 21Farenheit and I'm cycling at 12mph into a 24mph headwind, is the windchill calculated using 36mph?

Similarly, if I'm traveling at 24mph with a 24mph tailwind is windchill negated?
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Old 01-17-20, 05:07 PM
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Looks as if you have an answer in "Winter Cycling."
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Old 01-17-20, 05:23 PM
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Originally Posted by shelbyfv View Post
Looks as if you have an answer in "Winter Cycling."

The only reply in that thread makes no sense because Velocity cannot subtracted from nor added to Temperature.

i.e. 21F - 36mph ≠ -15F
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Old 01-17-20, 05:29 PM
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This is what google says. I Have no idea if it’s accurate.
“Calculate the
wind chill using the National Weather Service's new formula. Multiply the temperature by 0.6215 and then add 35.74. Subtract 35.75 multiplied by the windspeed calculated to the 0.16 power. Finally, add 0.4275 multiplied by temperature, multiplied by wind speed calculated to the 0.16 power.”
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Old 01-17-20, 05:48 PM
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Yes, use your airspeed.

When I still had a motorcycle I used a wind chill chart like this one. Note it has the same formula mentioned above
https://www.weather.gov/safety/cold-wind-chill-chart
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Old 01-17-20, 05:50 PM
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As windchill is a relative expression of an absolute (that is, temperature) being outside @ 21F riding into a 24mph wind, the temperature is 21F. Any exposed skin will experience the sensation of temperature around 5F. This is above the threshold for frostbite. Riding 12mph into a 24mph headwind is absolutely not 12 + 24. You're not somehow going faster into the wind than the wind is hitting you. Windchill would be based on the wind speed, and should be essentially moot, as I don't know why anyone would be going out with bare arms and shorts in 21F temps to begin with.

Meanwhile, I'm sitting here thankful I can never experience such conditions here. I don't think I've ever seen it windy with the temps below 40F or so. Most of our wind comes from the desert, so if it's windy, it's warming.
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Old 01-17-20, 05:52 PM
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My understanding is that this is the formula for determining windchill for stationary objects.

What I'm unsure of is if bike velocity and windspeed can be combined by simple addition to determine windchill "in motion", or if there is an exponential factor to consider as when two cars collide head on.

When two cars collide head on, each traveling at 15mph, the force of their collision is not the sum total of their combined velocities. Is it not the same when riding into a headwind?

Last edited by AllWeatherJeff; 01-17-20 at 05:59 PM.
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Old 01-17-20, 05:58 PM
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If your relative velocity is slower than the windspeed, the wind is never going to be hitting you faster than the wind is blowing.

If the wind speed is 20mph and your speed is 10mph, the wind speed is 20mph.
If the wind speed is 10mph and your speed is 20mph, the wind speed is 20mph.
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Old 01-17-20, 06:09 PM
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^^please reconsider. If on a still day at 40F, you set out at 60 mph (back to my motorcycling example), you are going to be very, very cold.
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Old 01-17-20, 06:10 PM
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Originally Posted by DrIsotope View Post
If your relative velocity is slower than the windspeed, the wind is never going to be hitting you faster than the wind is blowing.

I can't help but think that you would rethink your reply if you'd ever ridden a bike at any speed into 25mph headwind in sub-freezing temperatures, and then compared that sensation by turning around and riding 25mph with a 25mph tailwind in the same temperature. The difference between the two experiences is immense.

Whether bare naked or buried beneath several winter layers, loss of heat is an inevitability in certain conditions, especially if one of the factors you have to consider before riding is how long you can last in the wind and sub freezing temperatures should you have to repair a flat tire far afield.
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Old 01-17-20, 06:10 PM
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AllWeatherJeff speed is not the same as momentum
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Old 01-17-20, 06:18 PM
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Originally Posted by Darth Lefty View Post
AllWeatherJeff speed is not the same as momentum
They are if my momentum is carrying me along at 15mph into a 25mph head wind.


Are you saying that windchill is the same, regardless of whether or not one is moving or standing still?

This is the essence of my initial query.
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Old 01-17-20, 06:24 PM
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Originally Posted by AllWeatherJeff View Post
(Initially, I posted this query in the winter cycling sub-forum. But this sub-forum seems to get a lot more traffic)

If the temperature is 21Farenheit and I'm cycling at 12mph into a 24mph headwind, is the windchill calculated using 36mph?

Similarly, if I'm traveling at 24mph with a 24mph tailwind is windchill negated?
That makes sense to me. It's pretty straight forward. Windchill is the effect of wind on cooling down the body. With the wind at 0 mph, your net wind is your speed, and that's how your windchill is calculated. Years of riding in winter tells me this also.
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Old 01-17-20, 06:24 PM
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Originally Posted by Darth Lefty View Post
^^please reconsider. If on a still day at 40F, you set out at 60 mph (back to my motorcycling example), you are going to be very, very cold.
What is your experience of the difference between riding a motorcycle 60mph into a 25mph headwind versus riding 60mph with a 25mph tailwind?
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Old 01-17-20, 06:27 PM
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Originally Posted by mcours2006 View Post
That makes sense to me. It's pretty straight forward. Windchill is the effect of wind on cooling down the body. With the wind at 0 mph, your net wind is your speed, and that's how your windchill is calculated. Years of riding in winter tells me this also.
Thanks. I wasn't sure if there was some kind of exponential factor of momentum nvolved as when two cars collide head on.
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Old 01-17-20, 06:28 PM
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Originally Posted by AllWeatherJeff View Post
I can't help but think that you would rethink your reply if you'd ever ridden a bike at any speed into 25mph headwind in sub-freezing temperatures, and then compared that sensation by turning around and riding 25mph with a 25mph tailwind in the same temperature. The difference between the two experiences is immense.

Whether bare naked or buried beneath several winter layers, loss of heat is an inevitability in certain conditions, especially if one of the factors you have to consider before riding is how long you can last in the wind and sub freezing temperatures should you have to repair a flat tire far afield.
Riding 10mph into a 25mph headwind, wind speed 25mph.
Riding 25mph with a 25mph tailwind, wind speed 0mph.

And I reiterate: the wind speed is the wind speed; if you were to ride 25mph into a 25mph headwind, that doesn't magically make the wind speed 50mph. That's not how air works.
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Old 01-17-20, 06:42 PM
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Originally Posted by AllWeatherJeff View Post
You can't subtract windspeed from temperature, can you?
according this calculator I was waaay off, should have been -1.3 degrees when I added wind speed against you with your traveling speed (36 mph wind against you). don't know why that wouldn't apply. but this is not my area of expertise. gotta explain it to me like I'm 6

https://www.weather.gov/epz/wxcalc_windchill

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Old 01-17-20, 06:43 PM
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Originally Posted by DrIsotope View Post
Riding 10mph into a 25mph headwind, wind speed 25mph.
Riding 25mph with a 25mph tailwind, wind speed 0mph.

And I reiterate: the wind speed is the wind speed; if you were to ride 25mph into a 25mph headwind, that doesn't magically make the wind speed 50mph. That's not how air works.
Maybe, maybe not. I'm trying to determine windchill factor not windspeed, per se. But I can guarantee that standing still in a 25mph wind versus traveling at 25mph into that headwind at 21F are two entirely different experiences.


I may be mistaken, but what sounds implausible is that your response implies that at 21F with a 25mph wind that a body will lose heat at the same rate whether standing still or in motion.
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Old 01-17-20, 06:49 PM
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Merged duplicate thread. Please do not cross post.
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Old 01-17-20, 06:50 PM
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Originally Posted by AllWeatherJeff View Post
But I can guarantee that standing still in a 25mph wind versus traveling at 25mph into that headwind at 21F are two entirely different experiences.
Oh, for sure. I mean, traveling 25mph into a 25mph wind on a bicycle would take something between 1,700 and 2,000 watts. You'd be producing so much heat you could take your shirt off.

The windchill (relative) is as I said much earlier, around 5F, give or take. That's cold. If the wind chill were recalculated to say, -1F, would that make an earth-shattering difference?
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Old 01-17-20, 06:51 PM
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Originally Posted by cb400bill View Post
Merged duplicate thread. Please do not cross post.
Roger.
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Old 01-17-20, 06:58 PM
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Originally Posted by AllWeatherJeff View Post
You can't subtract windspeed from temperature, can you?

Look up the windchill equation .... it is a rather hilarious exercise of "why in the world is that the case???!!!"
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