If you have normal, run of the mill cupping, it likely due to underinflation. If the tire is inflated to the correct psi, and you still have cupping, it's probably from hard braking. All of my bikes have "cupped". Between the bikes being heavy, me being heavy, and me like to use my front brake(s). . . . a lot. . . . it's a given. I've used higher than spec'd tire pressures, but it doesn't seem to help. And, since it really doesn't effect the bike's handling. . . . I don't worry about it.