Insta-Freeze: A special kind of water that immediately solidifies upon hitting you or your bike.
If you happen to be fortunate enough to ride in places with fo' real winter, you've probably screamed expletives at insta-freeze first-hand, but with a few gear tweaks and homemade gadgets it doesn't have to be so bad. (For those of you who cheat and live in warm places, much of this also applies to mud and gunk, so read on)
First, let me digress a bit into why insta-freeze happens, because I think it's neat:
In order to turn water into ice, you have to take out energy. When water is sitting in a big pool, it takes a long time for that energy to escape because the surface area is very small compared to the amount of water and transfer of that heat off of the water's surface into the air is very slow, evern when it's very cold. Additionally, when water gets close to the freezing point, it becomes less dense so the colder water will float to the top of a pool, insulating the warmer water below and further slowing the freezing process. In the case of running water, the motion of the water adds enough energy to keep it from freezing. In either case, water can remain unfrozen for a long time after it drops below the freezing point, but it's ALMOST frozen.
That's where you come in.
When you ride through a puddle or stream you splash a thin film of water onto your bike. This thin film has a huge surface area compared to it's volume, so it is much easier for heat to escape. In all liklihood, your bike is also metal, which is an excellent conductor of energy. Since both the air and your bike are below freezing, and the surface area of the water is now very large, it only takes a few seconds for the water to finish it's transition to a frozen state, and in a short time you're riding a giant ice cube.
Since few things short of filling your frame with boiling water (don't try that) are going to keep water from freezing on your bike, the only alternative is to keep the water off.
The most vulnerable component on a bike, IME, is the front derailleur. When riding in ice (or mud), it's always the first to go. There used to be a number of options for "grunge guards" to cover the derailleur armature and keep it clean but they were bulky, heavy and never quite fit right. They're also nearly impossible to find these days. The image above illustrates how to use a soda bottle and a big zip tie to DIY a handy flap that deflects most gunk and keeps everything running smooth.
To make it, cut out a pattern similar to the one pictured at left (you'll have to tweak the flap shape and the cable cutout to work for your frame) from the side of a 2L soda bottle, making sure the curvature of the bottle is going into the drawing. Then attach the flap by wrapping the small upper tab around your seat tube and securing with a zip tie, and you're done. The flap will touch the top of your derailleur (that's what holds it out at an angle), but it won't affect the derailleur's operation.
Here it is in action:
Coming soon, more DIY weatherproofing for chains, rear derailleurs, cables and YOU.
[EDIT: not one, but two people went out of their way to tell me that my filthy bike makes for rotten DIY photos. I really appreciate the comments, though I reserve the right to snarkily call you out for being way too picky when you harsh on the well-used state of my ride . Here's some better pics of the little flap. I didn't really wash the bike, but hey, old habits die hard. Click on the images for higher-res]