I would like to know what effect changing the material of a set of disc brake pads would have on the rotors if you kept them the same. for example, If I have resin pads and have been using them for the life of the rotors, what would happen if I switched to metal or organic pads, while still keeping the rotors the same? Would they just squeal like crazy? thanks
I don't think you'll need to sand them. I would just change the pads and then go out for a ride on a borderline muddy day and splash through all the puddles you can find. You'll get grit on your rotors, which will accelerate the wear-in process.
If you do decide to sand them, be very careful. Everything I've ever been taught has been that you don't want to sand rotors, because it's very hard to sand in a circumferential direction (sanding as if the rotor were spinning and the sandpaper were still), which is the direction the rotors will be abraded during use. If you sand radially (moving the paper away from and towards the center of the rotor) you may run in to problems.
Depends on a lot of factors such as the rotor and pad make etc. The rotor has memory, left from the remains of pad material over time. What you can do is sand down the rotor surface lightly with medium grade sandpaper and then bed in the new pads as per the manufacturers instructions. Usually 10-20 hard stops without skidding. This will help avoid squealing etc as much as possible.