After you come indoors from a brisk winter ride, I know the last thing you want is to fuss with your bike. You want to warm you hands, have a nice meal and perhaps a warming beverage. But at some point, perhaps after feeling returns to your fingertips, you'll have to attend to your bike. Snow and icy slush, especially combined with salt and street grime, make a corrosive mixture that will eat through your bike and all its delicate systems.
To start off, use fenders. Not the kind that go on the seatpost. Real ones, front and back, that attach with struts and stay on. Like these:
They cost about $45 plus installation, but they will keep you and your bike drier and cleaner.
There is a some controversy about whether a bike should be stored indoors or out during winter. Without taking sides, I think it's safe to say that in Chicago you're usually better off storing your bike indoors to avoid theft. If you have the luxury of a porch, garage or basement, that's probably ideal. Otherwise, spread some absorbent matting in your living room or hallway where your bike can drip dry. Storing your bike in a vertical position may help in draining any water stuck inside the cable housing.
If your ride has been particularly messy, brush off as much accumulated slush as you can before bringing the bike in, and rag off excess water. Lubricate the chain with an oil formulated for use on bicycle chains (not WD40). Drip a little oil on each chainlink, and wipe off excess by running the chain through a rag with one hand while you slowly spin the pedals backwards with your free hand. Drip a little oil on the pivot points of both derailleurs (any hinge points at which the derailleurs flex), and a little more inside the jockey wheels on the rear derailleur. Do this at least weekly, and each time you ride through real slop. Following this ritual will protect your drivetrain from corrosion, excessive wear through the winter, and sudden breakage.
In winter, you should also regularly clean your bike, focusing especially on the drivetrain (the chain and everything it touches) and the wheels. This is also a good time to check your brakes. Pads can wear out a lot faster when exposed to salt and debris. If the pads get worn down to the metal, they will damage your rims (and fail to stop your bike). Keep the rims clean too, because this process can go both ways. Gritty stuff accumulated on the rims can speed up the wearing of the brake pads. Don't wash your bike at a carwash with pressurized water. That can knock grease out of bearings, and allow water to enter places it doesn't belong, like the rear freewheel or cassette, where it can later freeze causing all sorts of problems. Instead, use a bucket of hot soapy water, a rag and a stiff nylon bristled brush. Brush off the chain, all cogs and the rims of your bike. Dry everything thoroughly and re-lubricate as described above. (Find more winter bike maintenance tips at Chicago Bike Winter).
Rapid Transit Cycleshop does offer a winter tune-up package, where, for one set fee, we will take care of cleaning and maintaining your bike throughout the season. If you don't have the time, the space, the inclination, the patience or the ability to do it yourself, it just might be a great deal for you.