What type of Winter tires are most people getting for the G35 sport. Should I drop down to 17 inch rims? What width would be good 215? 225? etc.

 

I ran Dunlop Graspic DS-2 on my '03 and I'm going to try these on my '07. The size I believe I am running is 215/55-17. A smaller tire for snow is best to dig in. A wider tire tends to sit on top of the snow. As I recall at the time when I bought these there wasn't much of a selection that would also fit on my stock rims. I'm going to buy winter rims this time since my sport has 18" wheels.

The Bridgestone Blizzak WS-50 are really good snow tires.

 

If you're looking for something with a little higher speed rating, I would recommend the "H" rated Toyo Garit HT.
I'm going into my second winter with them on my '05 sedan (215/55-17).

 

The immediate past issue of Consumer Reports has a Winter Tire Test.