A month ago I purchased a 2016 M Sport 340xi with staggered 19 inch M Sport wheels and can't wait to get up every morning to drive it. I live in Colorado and need to soon purchase some performance winter tires. Thinking of the Pirelli Winter Sottozero 3 in a 225 45 18 square setup. I contacted a local BMW dealer and was told that the suspension is tuned for the staggered setup and if I use a square setup it will cause handling issues (rear end will be loose). The BMW dealership recommended 225 45 18 front and 255 40 18 rear. From reading other forums many 340 owners have used a square setup for winter and nobody has mentioned a downside like poor handling. Please reply if you have used a square tire setup for winter and let me know what you think of the handling. I bought the car for the performance and don't want a significant compromise in winter. Will buy a staggered 18 winter setup if I have to.