Standard offset is 35-38, 24 is about the lowest you can go without serious rubbing issues. With ET24 beemer wheels on mine the rear was fine but the fronts rubbed on harsh bumps & uneven cambers.
I have ET28 7j wheels, the front is fine but I've got 16mm spacers on the back which work out to ET12, and I need to bash my arches in a bit as it now rubs over bumps and with people in the back!
Edit: This is after lowering 40mm though...