Here are
a couple of articles I've written about brake rotors - or more correctly brake discs. Often times you will get a brake shudder after switching pads. Too many people diagnose it as a bad rotor. What is really happening is that the new pad material is interacting with the old pad material. The two types of material simply don't work well together.
You really have to clean your old brake discs if you're installing a new brand of brake pad.
Poke around my site for the 2nd article on brake rotors. I also just finished a 3rd article that is now in Vintage Motorsport magazine.
Richard Newton