I made both studded tires and chains for my 20" bikes this winter, no problem making for 16" also. I think I like the chains best, especially if you are going to fold the bike and take it inside a car, bus or similar. Chains can be used on your regular tires, no need to look for the knobby ones. Look in the Winter forums, there is a sticky for homemade studded.

I think the only problem with folders in the winter is if there is deep snow. That is no fun!