Just got back from a 10 mile ride at -3F, it felt like 20 miles. I find I ride everything in one chain ring lower in the winter. In winter I ride hours, and forget distance. If I'm in a dogsled trail, that might only be 3 miles in an hour. Sometimes it's a matter of how slow you can ride as you spin the crank. It's still faster than walking, and better than a gym. When it's colder than -10F, I try not to sweat, I just conceed defeat at the bottom of the hill, throw her in granny gear and get there when I get there. The post ride beer tastes just as good.