What is the recommended ice and snow tire for a C6, 4.2, sport,18 in rims?

in North America. Most people will say to get a slightly smaller and narrower wheel and tire package so the treads can dig down and find traction. It's much easier to just swap with the wheels with the tires already mounted, than to use one set of wheels for all seasons - and they get less chewed up than if you mounted and balanced multiple sets of tires.

and handle very well in rain & dry pavement. Good braking too. Search the C5 forum for the M3s for more info.

... you probably want to go with 17" or even 16", because the taller sidewall gives you better traction in deep snow. Want mine? Mounted/balanced on 16" S5s. I went to an A8 and need new tires this season.