The ACS Type 4 wheel sizes are as follows:

For a 645i -
9.0J X 20.0" ET 15 Front
10.0J X 20.0" ET 13 Rear

For an X5 -
9.0J X 20.0" ET 35 Front
10.0J X 20.0" ET 23 Rear

You need 20 mm spacers in the front and 10 mm spacers in the rear to match the ACS X5 wheel specifications.