One time, of accidentially riding your brakes down a hill, or getting them wet while they're hot, is all it takes to warp them. ( I.E. Car wash, after some driving, puddle, etc.)

Are you a two footed driver..?

General rule of thumb though, is to cut them once before installing them. I've seen plenty of brand new ones come right out of the box warped, simply from the heat created while machining them at the factory.

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