Rotors are surprisingly fragile, and it doesn’t take much to knock one out of true – extreme heat from dragging your brakes all the way down a descent can also warp discs. More often than not a few minutes with a truing tool will silence a disc that pings a brake pad as the wheel spins, but rotors can become deformed past the point of no return. If you’re wrenching away at a disc for more than 10 minutes and it's showing no signs of improvement, it’s time for a new one.