You absolutely need winter tires, especially in Vancouver since Dec 17th.

Best bet is to have a separate set of winter wheels, with dedicated winter tires. That way you can get a smaller wheel (18") and the tires will perform better in the snow, and not be as expensive as 20". Skip the all-seasons, and get the proper ones. I got mine at my dealer, but you can get non-OEM wheels as well.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue