Originally Posted by M3SQRD
The stock 245/40-18 PS2 has a rolling diameter of 25.7". The 235/40-18 3D has a rolling diameter of 25.4" so the fender-to-wheel gap increases by ~0.15".
BMW M3 270M winter wheels are 18x8"et20 and they recommend running a square 245/40-18 winter tire setup.
Not sure if it makes a difference, but I also have comp package.