Day 315: Wind chill calculator

14 11 2010

Despite the fact that it’s mid-November, it’s been surprisingly warm the past few weeks with temperatures in the 60s and 70s. I’ve found that once temps get in the low 60s I have to start layering my clothing when I go out for a ride. (Recently I discussed my lack of motivation for riding in cold weather.) Today, I enjoyed a nice 15 mile ride with temperatures in the low 50s. I know the good-weather days are going to end soon as Winter moves in. While I was riding today, I wondered what exactly the wind chill was. My math skills leave a lot to be desired, so I turned to Google to search for a good explanation on wind chill and how it’s calculated. This chart from the National Weather Service was pretty helpful:

National Weather Service wind chill chart

Apparently, this is the formula the U.S. National Weather Service uses to calculate wind chill:

T(wc) = 0.0817(3.71V**0.5 + 5.81 -0.25V)(T – 91.4) + 91.4
T(wc) is the wind chill, V is wind speed in miles per hour and T is the temperature in degrees Fahrenheit. 

I have no idea what this means, nor how to calculate the numbers. (I was an English major – math frustrates me.) Maybe some of you can make more sense of it. Or perhaps I can just use a calculator like this one or this one. I found some good information at IceBike.org. I wondered how wind speed differed from cycling into the wind. According to IceBike, cycling into still air is the same as wind speed. Okay, I guess that makes sense. But does the wind chill factor change if a cyclist rides at 15-mph into a 10-mph headwind on a 40-degree day? Or is that the same as what’s stated on the chart? I’m still confused.

Today’s food journal:

Lunch:
— Organic LF yogurt with granola = 5 points

Snack:
— Power Bar = 3 points
— 1 cup LF chocolate milk = 3 points

Dinner: (at restaurant, so I’m estimating points as best I can)
— Black bean lasagna = 13 points
— Iced tea = 0 points

Snack:
— Skinny Cow ice cream = 2 points

Life’s a journey. Enjoy the ride!

         _O
        \<,
…( ) / ( ) 

Thanks for visiting.

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4 responses

14 11 2010
Dave M

It’s the vector sum of the wind speed and the bike speed. Thus 15mph bike with 10mph head wind is 25mph. 15mph bike with 10mph tail wind is only 5mph. 15mph bike with 10mph cross wind is (Pythagorean theorem) sqrt(100+225) = about 18mph. Other angles are going to require you to bust out the law of cosines, which you can find on wikipedia.

15 11 2010
Alice - cyclingproject365

Aah. Thanks Dave! That makes sense — until I got lost with the cross wind Pythagorean theorem and cosines. My math skills obviously leave a bit to be desired. Thanks for your help!

14 11 2010
Tom

Alternatively, you can use a scale like that “real man’s” torque wrench found on Sheldon Brown’s site, found here: http://sheldonbrown.com/tork-grip.html

I would imagine the readings would range from “cool” to “chilly” to “cold” to “darned cold” to “S&$^! It’s f@#*&ng FREEZING!”

15 11 2010
Alice - cyclingproject365

Perfect! I think that’s all one really needs, isn’t it? “Cold,” “damned cold” or “@(#$& freezing” (at which point I definitely won’t be outside riding.)

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