Warm objects, such as your air-cooled engine, lose heat when exposed to cooling air. If there’s no local air movement, as when you’re sitting at a stop light, heat radiating from your engine will hang around and warm the air around it. And you too, if that light doesn’t change.

However, moving air carries heat more effectively than air that’s not moving, so when the light changes, off you go to cool off. The greater the wind speed, the faster heat is lost.

Wind chill works the same way. When you’re moving, you feel cooler than when you’re sitting at the light. Your engine cools down too. That’s the wind chill effect at work.

How much wind will a wind chill chill? In the fall of 2001 the National Weather Service began using a revised wind chill formula based on new research on how wind and cold air affects people. Wind chill tables are designed to indicate the dangers of different combinations of wind and temperature on the bodies of humans and animals. The old wind chill formula was based on experiments with a can of water hanging on a pole in Antarctica in 1945. The new index was tested on human subjects and is based on heat loss from exposed skin. Science marches on.

You can see from the new chart that on a cool day, say about 50 degrees, riding your bike unprotected at freeway speeds will cool you down enough to chill your beer. If the weather drops just five more degrees, you could freeze your latte.