Doug Westly | Safety Editor
IMPORTANT NOTICE: Ultimately, the safety of motorcycle riders and their passengers is their own responsibility. Nothing presented in the column supersedes, negates or relieves a motorcyclist and/or passenger from assumption of personal responsibility for their actions and safety.
Yes, winter is over, unless you’re on tour in Australia or
New Zealand. So why do you need to think about windchill?
Windchill is not just for winter. It can occur in (just about) any
climate, under different weather conditions.
There are lots of definitions for windchill. For our purposes,
let’s just call it the perceived decrease in temperature
felt by the body as a result of airflow across exposed skin (although
some measurements also use a clothed body).
We lose body heat through either radiation, conduction or
convection. In the case of windchill, it’s convection that is the
culprit. The air moving across our body, it disrupts the layer of
warm air formed by the body (known as the epiclimate), allowing
cooler air to displace the warmer layer. This cools the skin
surface. The faster the air flow, the faster the surface cools.
Windchill doesn’t just happen in winter, at freezing or even
cold temperatures. Anytime the warm epiclimate is disrupted
by cooler airflow, windchill results. As a motorcycling example,
at 50 degrees (F), an airflow of 70 mph will result in
almost a 12 degree drop in perceived temperature. See the accompanying chart.
Now for the technical part, just for you “I gotta know”
types. There are different formulas for calculating windchill.
Part of the discussion is whether or not the calculations should
include allowance for clothing. It’s also calculated a little
differently between the U.S. /UK and Australia (just in case
you are currently on the aforementioned Australian tour right
now). For our purposes, the formula looks something like this:
Wct = 35.74 + 0.6215T – 35.75V (**0.16) + 0.4275TV(**0.16)
where Wct is the wind chill index, based on the Fahrenheit scale T, is the air temperature, measured in °F, and V is the wind speed, in mph. (Source: NOAA)
Interestingly, the U.S. /UK formula does not factor in humidity, even though that can be important for those of us who ride in humid climates like Flatistan (Florida). You would think the English at least would figure out humidity is kind of important in the algebraic effort. However, those of you on the Australian tour can rest easy on this issue, as the Australian formula does factor in humidity. This just demonstrates that how windchill is calculated depends on where you are riding.
By the way, windchill is generally only calculated at 50 degrees (F) and below. However, that does mean that even in summer, if you start out on a brisk 48 degree (F) morning, you could be surprised by some windchill impact. Even at ambient temperatures above 50 degrees (F), windchill can occur under the right circumstances (higher speeds, exposed skin, wet conditions, etc.).
Speaking of which, if you get wet, it becomes even more complicated. Moisture on the skin cools it even more, and accelerates/ increases the windchill effect.
So what does all this mean to us, as motorcyclists?
First off, we need to recognize that (in sub 50 degree (F) and/or wet weather) as our speed increases, the effect and impact of windchill become more critical. Referring again to the chart above, we see that it only takes a little bit of wind to impact our body temperature. Even above 50 degrees (F), windchill can become a factor. Continuous exposure to windchill is for all practical purposes the same as exposure to actual temperature, as represented by the windchill formula. Bottom line: You and your body get cold. Get too cold and you go from merely cold to hypothermia pretty quickly.
How do we fight windchill? First off we have to recognize the phenomenon exists, and that it can affect us even in moderate ambient temperatures. Fortunately there are several steps that can ward off windchill.
Understanding the nature of windchill gives you an advantage. Checking the weather report before riding to get an idea of temperature and humidity factors (not to mention the possibility of rain) is critical. Make sure you are equipped (gear) to handle possible windchill conditions. Bare skin is probably the number one problem with windchill. Dressing in layers, so you can adjust to the changing temperature and weather/riding environment is always a good idea.
Finally, if you start getting cold, don’t wait to take action. Don’t think “It’s only another 60 miles. I can make it.” That only guarantees a miserable ride and possibly could convert your windchill and lowering body temperature into the initial stages of hypothermia. It’s not macho or impressive to anyone who watches you try to “tough it out.” If you start getting cold, stop. Take a break. Readjust your riding gear. Add a layer(s).
Understanding windchill and how it impacts you is just one more mark of a good rider. Use your skill and knowledge to have a safe, fun ride.
Ride Safe – Ride Smart!