I rode to work in sub 20 deg. weather and leaned my bike against the wall in the high school classroom where I teach. A few minutes into the first period I heard a loud "poing!" and asked the class if anyone had just thrown something at my bicycle wheel. The biggest clown pointed to the quietest girl and said "she did it." I decided it wasn't anything to get too excited about but when I got ready for my ride home I discovered one of the spokes had let go. I continue to blame it on the change in temp. unless someone out there has a better theory.