I've been nose and mouth breathing since I started cycling a year and a half ago mainly 'cause that's how I was taught in Physical Ed a long time ago. But I was struggling a bit with my breathing, not getting enough oxigen I guess, mostly on climbs and when riding in the aero position (TT bars), yesterday I tried something completely different, by accident, and voila!. It was very cold yesterday 32F and my nose was running like mofo, so I started inhaling and exhaling through my mouth, it was "efen" incredible man, I got into this sweet rythim and my probs were gone.