To keep your Avid X0 Trail brakes functioning properly, check your pads for wear and replace them when necessary. Organic compound pads are softer for quieter braking and increased modulation, while metallic pads dissipate heat better and last a bit longer.
Two pads, one retraction spring and a retaining bolt are included (enough for one brake) in each pad set. And, there's an aluminum backing plate option if you're really counting the grams.