I have winter driven my Z4 3.0i for the last 4 years, the last 3 have been on hakka 7s non-studded (225/40/18 square on 18x8) and they have been awesome. There is noticeable tread squirm in the dry, but once there is snow on the ground, they are almost unstoppable. Limiting factor becomes ground clearance. The amount of grip they provide is truly amazing, and provide a lot of control when you WANT to go sideways