It was a sunny day, but the temperature barely got above 40 degrees. Riding a motorcycle in 40 degree weather may not sound unreasonably cold until you consider the wind chill. I had always been curious about exactly what wind chill means, so I did a bit of research about it ten years ago. Basically, it has to do with how cold a person feels due to the effect of wind. Not a big revelation. The calculations are based on a formula, which was arrived at through empirical means. The literature consistently makes the point that the calculation of wind chill is just an approximation but you would not think so based on the following formula.

T = temperature
S = wind speed
Wind chill = 91.4 + ( T – 91.4 ) x ( .474 + .304 x sqrt(S) – .0203 S )

I actually found a number of different formulas. The one above is the one I was actually able to replicate in an Excel model and get the same results as the published table. Apparently the calculations are not as accurate at higher temperatures and wind speeds because most of the tables only go up to forty degrees and the wind range in the tables typically goes up to 20 or 30 miles per hour. My interest was different, however. When riding a motorcycle, in effect, you create your own wind, and on the Interstate, it is 65 miles per hour! My estimate of the chill factor at 55 degrees and 65 miles per hour was that it felt like freezing. The formula above yielded 33 degrees. A lot of work to confirm what I had guessed, but I feel better knowing.  The sunny 40 degrees today at 40 mph produced a wind chill of 26 degrees. I could not bare to ride at 40 degrees without using my Widder electric gloves and vest.