I noticed when rotating the tires on my GF's car that the pads are getting close to needing replacement. I also noticed the rotors had a lip on the outside edge. More so than i've ever noticed on any of my cars. Guess i'm curious if I checked them whats the minimum thinkness that they can be turned and remain safe? Looks like they have never been turned. Car has 73k miles on it.

Chuck

 

I would say just replace when you do the pads if there is a deep enough wear that there is a lip. From what I have been hearing, the OEM rotors in general are not very machineable, and with 73k, it sounds like you have gotten you money's worth!
If they are machineable, they are more likely to fade/warp...so consider the way that the car is driven when decideing.

 

OEM rotors on most BMW cars are very soft compared to other makes.

My sister's '02 MC had about 45k on it when the brake pads went out. The rotors did not have a bad lip on them so they were turnable. She drives pretty easy though.

My stock brakes only lasted about 20k and the rotors had about a 2mm lip on them. I chose not to have them turned because of risk of warping under heavy use.

Current brakes have lasted me 45k and have bout 20k left in them by my estimation. This is under the same conditions that wore the stock out in 20k.

Brakes on my car:
Hawk performance ceramic pads
Powerslot cryo-tempered slotted rotors
Goodridge SS brake lines
Motul RBF 600

 

Ok thanks both of you.