You don't have to stop riding in the winter. You just have to dress correctly. I find that most riders don't seem to know how to dress for winter riding, and therefore don't seem to get out on the bike as much as they could. Correct apparel is critical to an enjoyable winter ride. You can always tell the inexperienced winter riders, no head cover, full jackets, and light gloves. All wrong! Let me explain.
The key to winter riding is to not sweat. Sweating, while unavoidable on a hot summer day on a fast ride, is to be avoided for winter riding. When you sweat, the moisture chills your body. You become uncomfortable quickly and want to cut the ride short. Dressing properly avoids sweating, and allows you to ride longer distances, but not as hard or as long as you might in the summer.
The first rule of winter riding is you want to be cold at the start of the ride. If you are toasty warm at the start of the ride, you are over dressed for sure. When you start riding, you should be cold. You should not be unbearably cold and shivering, but colder than you would otherwise be comfortable with. This should pass as you start to ride the bike in the first few miles, when you should become just cool, like you have walked into a room with the air-conditioning set on full blast. This will pass as well once you get into the ride. But you should always be cool, think cold air conditioning on a hot summer day.
There are three basics to remember in winter riding:
There are two other techniques you might want to try for winter riding to keep the chill away. The first is drafting. While drafting in the summer is all about conserving energy, drafting in the winter is all about getting out of the wind. The less wind, the less heat you lose. The other technique I find extremely helpful in getting warm while on the bike is a quick stop out of the wind if you can't seem to warm up. Say you are 5 miles into the ride and you are still uncomfortably chilly. Stop out of the wind for 2-3 minutes. You don't need to go inside, but just sit out of the wind and preferably in the sun. Your body will continue to generate heat, but the wind will not be taking it out of you. Once you warm up, continue on the bike. You will now be warmer, and the wind will have to remove that much more heat. A hill is also a good way to generate some heat, just don't over do it. Remember, you don't want to sweat. If you find yourself getting toasty warm, unzip, sit up, slow down, or find that downhill to scrub off the extra heat.
I dress according to temperature. I break everything down into 10-degree increments or bands. At the high end of a specific band, you might find yourself tossing an item or two, and at the low end, you will be a little chilly until that first hill. You will notice in the following descriptions that prefer natural fibers like silk and wool. I find they work better than synthetics. Wool is remains warm when it gets wet and is comfortable in a wide range of temperatures. Silk keeps you warm with friction as well as its insulation properties, and it feels great to wear. The only synthetics I wear are summer riding clothes, tights, gloves, and some fleece around my head. The rest is wool or silk.
My first band is 60 degrees or above. This is full summer riding apparel, shorts all around.
My next band is 50-60 degrees, when it starts to cool off in the fall, or late spring. For this, you want to wear arm warmers, glove liners and something light on your head. All these things are easy to remove and stuff in your pockets as the day warms up. I use a silk balaclava for my head. I can double fold it over my ears, and it keeps the heat from my head from being whisked away by my helmet. Glove liners cut the chill to your fingers, but don't trap moisture, and arm warmers keep the chill off parts of your body that don't get as much circulation as your legs or torso.
At 40-50 degrees, you need to think about covering your legs. I use leg warmers, as they are easy to remove if the day warms up. Tights may get too warm later in the ride. For the hands, I switch to a light glove with a glove liner. You can easily use one or the other if it warms up during the ride. For my head, I use the same silk balaclava, but add something around my ears, like a fleece band. I also put a silk undershirt under my jersey. This keeps your torso a bit warmer, but not too warm. I also bulk up my socks to a SmartWool or similar thick sock.
At 30-40 degrees, you have to assume the day will not warm up much. The first thing I do is upgrade to running tights I wear over my normal summer cycling shorts. I also upgrade to a full ski glove with liners for my hands. Remove the liners if your hands are getting too warm. For my head, I use the same balaclava and then a large wide fleece band around my ears. For the torso, I wear a layer of silk, then a long sleeve wool jersey, and finally a summer jersey over the whole thing. For my feet, I add a neoprene toe cover and the thickest wool sock I can find. You don't need a full foot cover, it will just make your feet sweat and get chilled. Your heals never get cold, just your toes, so keep them out of the wind with a toe cover and let the rest of your foot breathe. Also don't wear your shoes tight. Keep them as loose as possible, as this will keep in air, a natural insulator. You also might consider putting duct tape over any vents in the shoes to keep the warm air in the shoe.
At 20-30 degrees, I upgrade to mittens with glove liners for my hands. I also add a neck warmer. This keeps the wind off the last visible bare skin except for your face. You can also pull the balaclava over more of your face to keep the wind off of it.
Below 20 degrees, I go skiing.
So there you have it, a simple system to keep you riding (or skiing) all winter.