A good amount of us are also running 235/40-18 up front (on stock 7.5"). Under most manufacturer's recommended 8-9.5" wheel width with no perceived ill effects. Not ideal...but helps with the understeer, and improves the ride.
That width/aspect ratio was stock on an M3 at one point (235/40 on 7.5"), so it's not exactly reckless.
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