Like a lot of bicycle enthusiasts who live in cold temps, I ride regularly in feezing temperatures.

Temperatures down to 20 F (-6 C) can be done without a great deal of grief. Below that and you will start to think about taking the car.

Below 10 F (-12 C), and you have to be extremely careful with your clothing. Any mistakes could cost you skin from frostbite - quick.

My personal opinion is that temperatures below about -10 F (-23 C) is pretty punishing and dangerous. Some guys do it, and I have also bicycled in temps below -10 F (-23 C), but I question the wisdom of it.

At cold temperatures, though, you need to cover your skin. For breathing, use a balaklava to cover your nose and mouth. You can damage your throat and lungs by gulping freezing air.