Here are a few tips for winter cyclists. These tips can be applied to a wide range of temperatures and conditions. Use your own judgment as to what you need to make your winter riding more enjoyable!
Tires
Wide tires with widely separated knobs work best on snow. with low pressure.
Lubrication
Bicycles don't need to be "winterized" the way cars do. The loads on bicycle bearings are so slight that just about any grease will protect them. You can use low temperature grease in bicycle bearings to make them easier to pedal and steer. If your bike works in the cold, it's already "winterized."
On the other hand, bicycles that are used regularly end up with more dirt and water than grease in their bearings and yearly repacking will make them last a lot longer So you can repack the bearings with low temperature grease and call it winterizing.
Find a lubricant for cables that stays liquid. . This can help your bike shift better in winter. Gore-Tex cables require no lubrication, so they work well no matter how cold they are.
Lighting
Illinois requires bicycles to have a white light in front. I strongly recommend a red light in back; Red flashers that meet this requirement are available for about $16. Headlights that meet the state requirements also start at about $16 These are basic, non-rechargeable lights that will make you legal, let you be seen and help you see under some conditions. This is often enough. However, people who ride longer distances and in all conditions usually use more powerful lights. .
Both front and rear lights should be visible at 500 feet. Wheel reflectors and pedal reflectors are really important as well.
Reflectors are available as vests, straps, tape and plastic pieces that you can wear or mount to bicycles. Make yourself as visible as possible.
Clothes
Cycling generates a lot of heat so clothes that are warm and comfortable have to control the buildup of heat and moisture as well as insulate and protect from wind.
Your particular metabolism, physical condition and riding style will determine what's needed to keep you warm. You'll have to experiment.
Your outer layer on top and bottom should have a windproof front and breathable sides and rear.
Layer various weights of clothing under your outer, breathable/windproof clothes. Multiple light layers with neck zippers let you adjust your ventilation as you ride.
Your base layer (against your skin) and mid-layers should be synthetics or wool. Cotton in these layers will feel wetter and colder.
If you feel warm as you start out then you're probably overdressed for any ride longer than a half hour.
Disposable heat packs can be part of your normal system or can be carried for emergencies. They come in hand and foot varieties and last for 2-5 hours, depending on conditions.
Neck gaiters and balaclavas are variations on the theme you may find useful. Your face, head and neck will need different amounts of protection as conditions vary. Uncovering your head is usually the simplest way to dump heat. You may need to change the sizing pads in your helmet or remove them entirely to fit your winter headgear.
You'll find eye protection very helpful if you're riding in a headwind or falling snow