[GP20]

Those offsets won't work with a regular Z4, especially lowered on H&R springs.

A front 8.5" wid rim with an offset of ET35 is basically at the cut-off line before the tires would rub the inner front bumper plastic liners. With an 9" wide rims, you'd need something with an offset of ET 42, and even then there's a great chance that the inner part of the wheels would rub against the front struts housings.

I had 19x9.5 ET42 (rear rims) SSR GT3's on my '04 Z4 3.0i lowered on H&R springs and it seemed to be another 7~8 mm before the tire would rub the edge of the rear fenders. With an 19x10 rim, you'd need something closer to ET50 than ET42, in which case, again, you risk having the inner wheels rub again the shocks.

My recommendations would be to go with 8.5" front rims and 9.5" rear rims at the widest.