Originally Posted by BMW M Power Mexico
Rotor depth seems to be ok, a lip is developing but not very deep yet though I have no way to measure exactly.
On the hub part of the rotor they have inscribed the rotor minimum thickness which is 28.4mm if I remember. On my car you can clearly see it without taking the wheel off. I would believe lip is OK as long as you are above the minimum thickness.
I use this
to measure when I take the wheels off.