I've ridden this fall in a couple of sub-zero (Celcius) mornings, but no colder than -4C/25F so far. I haven't had to cover my face but I'll wear a cycling-specific toque under my helmet below 6C/43, lobster mitts over my gloves below 3C/37 and booties over my shoes below -5C/23F. I'm putting together notes on temperature, what I wore and whether it was good, too much or not enough.