I ride all winter long on 32 mm 700C tires on a hybrid bike, with a little tread pattern (definitely not knobby). Thinner tires are better in the winter for me . . . they punch through the snow and give you traction on the road. The only time that studded tires would be nice is when it's extremely icy, and frankly, I don't trust biking around the cars when it's that slippery. The areas that my hybrid really shines over my road bike for winter riding:
- Cheaper components. This is a big relief every time a wave of salty slush sprays over you and your bike.
- Thumb and trigger shifters are a lot easier to manipulate with gloves on than STI paddles (which always seem to get my fingers caught)
- v-brakes stop better than the cantilevers I have on my road bike. You do want a brake that has decent clearance for sticky snow/ice, otherwise your brakes are constantly grabbing and slowing you down as you ride through all the crap.
- The road bike has a skinnier chain (30 speed) and I don't trust it to handle the same amount of wear and tear that the thicker chain on my hybrid 24 speed would.
- The hybrid has easier gearing. You go much slower in the winter, between the cold, the snow, the blowing winds, and the ski-pants. Having those easier gears really makes a world of difference when you come to the super-mountain that every winter destination seems to be on.
Of course, any winter bike NEEDS decent fenders and lots of blinky lights since most of your riding will be after dark.