Some years ago I replaced the stock rotors for slotted and drilled on all four wheels of my 2003 Monte Carlo. At the time I needed to replace the rotors and they had a habit of warping. The new rotors work great and way outlasted the old ones without a hint of warping. However, after putting them on my car (along with new pads) I started having rings appear on them like this:
This picture is from the front wheel, I have one on the back wheel that is mostly rust ring with 2 small normal rings. I have considered replacing them but I have not had any impact on braking performance (even with the few times I have had to stand on the brakes) or funny handling in all types of weather.
I have changed out the pads once thinking it would clear these up, but no luck. I don't know what the insides surface look like either. I'm in need of new brake pads now and wonder what I can do to improve this situation. I have read up on turning the rotors and know what it takes to do it with slotted and drilled ones. I barely drive this car as it is and they are not warped so that is a last resort at best.