I did some research on de rear rotors, and E46 rear rotors will not fit properly on a E85 Z4 (3.0i).
some dimensions from brembo:
E85 (3.0i)
E46 (330i)
First of all the parking brake won't fit: E46 rotor inner diameter is about 1 inch bigger. There is someone who made his own parking brake pads (to fit 330i rotors on a 323i which has also small parking brakes) by welding in a 323i brakepad on a 330i pad. But that still won't work for the e85.
Secondly you can clearly see that the offset from the disc itself is much less on a E46 than on a E85. So the caliper wont fit unless spacers are used between the caliper carrier and the trailing arm. This offset is probably changed to give the E85 a different trackwidth or to use rims with different ET/offset.
Next I looked at the X3 rotors:
320mm rotors, offset and depth for parking brake may seem doable, but still big parking brake pads needed.
The only rotors that may fit are the e90 rotors (up to 320i):
They are only slightly bigger (300mm), and offset is slightly different (3mm).
Not much difference to the stock e85 3.0i rear rotors
But when fitting 1 or 3 series rear performance calipers on a Z4 this is how it looks like:
On the inside diameter a slightly bigger rotor is better
On the outside the calipers can take up to 320mm
about 0,5mm room between rotor and caliper on the outside
Lots of room on the inside so thick rotors is no problem.
Maybe the e90 rotors are the best option. The rotor is a bit bigger (so the brakepads fit the rotor better on the inner side and every bit of rotor on the outer side/diameter is better), and the parking brake will probaby fit. There is less offset on the rotor, so a simple spacer between the caliper and the trailing arm (4 or 5 mm) will do the trick I think.
Only thing is that the face plate of the E90 rotor is thinner, and there's a 45deg. edge. If there's a slope on the edge which will take op space, that might be a problem.
That's what I've found out so far
Has anyone any ideas which might be of use to me to fit these calipers best?