Let me clarify I bit further... I see 3 options:
- Normal OEM staggered sizes - 255/40/18 and 275/40/18.
- 1 size down staggered sizes, 245/40/18 and 265/40/18. This is what Tire Rack seems to recommend.
- 255/40/18 square. This is what will come on the BMW winter packages, but the wheels are narrower than the 513M's.