Even tho it could be 40 here in Denver on a nice sunny winter day, lots of times, depending on the elevation you go to, some of the valleys and or canyons could be 10-20 degs colder. That is at a stand still. At speed the temp starts to drop dramatically. Check out a windchill chart. When I was commuting to work everyday, and better aclimated to the colder temps, 25 was the lower limit for no heated gear. That was for a 20 minute ride. Anything under 35 now requires the heated gear. I must be getting old....