I need a little help thinking through what I need to do to my bike to continue to commute during Philadelphia's short but messy winter. Typically, we don't get snow and ice on the ground until January/February, but every year it seems to surprise me and I'd like to get a jump start on planning. Here's the situation: neighborhoods are rarely plowed or salted and in the downtown, snow is plowed into the bike lane. I need to be able to ride about 1.5 miles on packed snow with patchy ice (the unplowed neighborhood) and then about 3 miles on possibly plowed but also possibly icy streets/bike lanes with lumpy packed snow and patchy ice. I commute on a Jamis Coda Elite (steel, disc brakes) but also have an old Raleigh mountain bike (aluminum, cantilever brakes) I could use.

Should I just stick studded tires on the Raleigh and reserve it for the icy days? (I did read the excellent thread on winter tires.) I love my disc brakes for quickly stopping for jerk driver maneuvers, though--should I invest in a second set of wheels for the Jamis and put the winter tires on them? What else should I be thinking about?