I agree. Find a used 18" rim/tires setup for the winter. People are always selling them on here. You can save yourself a lot of money since they're about $1800 new on Tirerack.
2013 M3 - Mineral White, Carbon Fiber Roof, Competition, Cold Weather, Premium, 6MT, BPM Stage 2 Tune, MS Stage 2 Intake, Challenge Race X-pipe, M Performance Wheel