I saw Ryan, the coach of Zap Fitness say to use tights if it is under 50 degrees. I sometimes use half tights, but once you get going it doesn't matter. Case in point, the Club 2008 Cross Country Club Championships when it was like blow zero with a killer wind chill , l am from the south and made the mistake of wearing tights in that race and l was one of the only runners in the race with them on. It really dosen't make a difference once you get going. Your hands and head are the most important, as well as your upper body. I went to college in the Midwest and never wore tights all those years.