@Dirt: my “regular” tires, that came with my Specialized bike, have a smooth rolling surface — no tread at all. The outside edges are knobby, so they provide traction on curves. I think they’re great, but OF COURSE they don’t do well on ice. I just never thought about getting different tires for winter, whether studded or something else. A separate set of tires is an expense, but compared to the cost of car maintenance, it’s not much. Thanks for the tips.