It's amazing how comfortable 30°F can be once you get moving and build up some heat. The toughest part for me is getting out the door and on the bike. That said when it stats getting close to 20°F the mental hurdle becomes quite a bit more challenging. But in the winter the biggest detractor to riding outside for me anyway are the roads. Roads are salted heavily in my area and I don't want that crap all over my bike. And when the snow starts sticking and building up on shoulders safety is a big concern.