I am an Ironman. That's right, I've done the 140.6 deed multiple times. Do it once and it's an accomplishment. Do it twice and it becomes an obsessive. I have decided (much to the wife's lament), that I will keep Ironmanning until I qualify. Qualifying requires training. Tough training. Mentally and physically. Which includes biking...
I live in a clime non-conducive to outdoor cycling. You can't really bike in the cold anyway. Repeated studies have shown that riding when the temperature is below does more harm than good from a fitness perspective. For one, ice biking is not good for the legs. My legs are the engine. They are the heart and soul of the race. Here's the risk and a brief review of physics. At increased speeds, moving air increases the number of collisions between you and the climate. This, in turn, causes evaporation and its cooling effect. If the temperatures weren't already cold, this would have a positive effect on training. However, at cold temperatures, muscles don't achieve the optimal workout temperatures. Enzymes in your muscles work slower. Internal muscle heat could drop to dangerously low levels. I wouldn't want to risk frostbite or amputation for some outdoor miles.
For two, low temperatures impair the ability for lungs to absorb oxygen. A brief review of anatomy. As humans, we have advanced gas exchange adaptations, possibly the best in the animal kingdom. Your lungs are moist organs that serve as a barrier between you and cellular respiration. The volume of liquid is spread out increasing the surface area. Increased surface area allows for higher levels of oxygen absorption with simultaneous excretion of carbon dioxide. In cold weather, the exchange system is compromised. Due to their diminutive size and large surface area, tiny icicles are prone to crystallize in your alveoli, perhaps endangering your VO2 max in later months. I wouldn't risk it.
To further complicate matters, cold weather biking is not good for the bike. Yes, I own 2 bikes (one aluminum road and one carbon tri). Neither bike is made of a material that is necessarily corrosive. It's not the bike itself, but the components. Cables, cogs, pedals, connectors, nuts, bolts, etc. are all oxidation prone. Brief chemistry lesson...salt is a chemical catalyst for the reaction between metals (specifically iron) and oxygen. Iron, such as the kind found in the components of my precious multi-thousand dollar rides, reacts slowly with air to form a reddish-brown compound known as iron II oxide (commonly called rust). Add salt and the energy required for the reaction is greatly reduced, allowing the reaction to occur at insultingly low temperatures. Salt is good for roads and bad for ice. Worse for my bike. A bit of research will show that riding in poor-climate conditions negates the warranty on the bike. I value and cherish my ride. Risking that much money and integrity of my bike is not worth the challenge outdoor riding offers.
Understand, that these aren't scientific studies. They're more the kind that I invent to justify not riding outside. It eases the guilt. In all reality, I am a big pansy when it comes frigid pedaling. My feet can't seem to produce heat between November and March. I see many cyclists in their outdoor gear with snow on the ground and temperatures below the Mason-Dixon line. I am not sure how they do it, stealing my masculinity like that. Who do they think they are, all bundled up, spinning on their single-speeds, gloating on by not even nodding in my direction as I sit in Starbucks, sipping on my cafe mocha? I see them. I scowl. I swear. Jerks. I am going to change into my bike shorts, no shirt, no socks, and mount my ride on the roller trainer in front of the TV. I am going to do drills and monitor my HR while happily sweating in the relative comfort of my basement. I'll see you in March. Or April. Definitely May.