+100 snow tires! Get a dedicated 17" wheelset. It'll pay for itself after a couple of seasons of not having to pay for mounting and balancing. I found a used set of OE 17's on this forum or Tire rack sells 17's that fit.
2007 E90 335i, TiAg, 6AT, ZPP, ZSP, ZCW, 6FL, HD
Quaife lsd, ETS fmic, GIAC s/w, Dinan intake/exhaust/oc, KW/GC/M3/Meyle susp, Apex Arc 8, Mich PSS