You need about 1/8" overall off the snout of the rotor. So if you set the lathe up starting at 0 you would end at .0625 at the cutter. Also want it about a 3/8" deep towards the wheel mating surface in my experience.
Do your wheels have a chamfer or just a step where it necks down?
My wheels have the same chamfer, because of my calipers I use a 3/8" spacer currently.
