It will be different for the e90 and e92
For the fronts (on both models), you can go 19x8.5 with an offset of 30-40
The rears are where the offsets will differ (even between pre facelift and facelift sedans)
On the e92 rears, you can use a 19.9.5 et30-35
Or 19x10 with an offset 35-38
You will have to roll the fenders, if you're lowering the car... or depending on how low you go
The offset basically determines how far in or out the wheels sit - the lower the number, the closer it will be to arch
I am using 19x10 et37 at the back with 265.30.19... car is lowered, and fenders rolled
Can load the car, and no touching