This winter when I changed from the OEM tires to the snows, I noticed that there was rust on both front rotors. I'm guessing it's because the front disc brakes aren't used unless you have an emergency stop. Would this be correct? Would it make sense to do an emergency stop once in a while to clear off the rust?
They are used, actually, every time you stop, but often not until you are under 7mph and, thus, very little wear. If you want, occasionally you can get going at a decent speed (55-60?), put the car in neutral then stop that will cancel regenerative braking and allow you to 'polish' the rotors. Repeat that cycle a couple times. As I understand it from those who know more about brakes than me, this isn't really necessary.
Yeah, occasionally the disc surfaces will have rust. They're usually cleaned by my dad who rarely drives the Prius so he tends to brake harder, getting out of regen quicker and thus cleaning the rotors. I do clean them as the doc above describes if my dad hasn't driven the Prius in a while.
