An good question. We used volume 31 with my friend's iPhone connecting wirelessly with the Led Zeppelin song. This was loud, but probably a lot of people would have it there for a song or three (not me). The song was Fool in the Rain, which has a three beat thumping bass line rift.
While Fool in the Rain was playing at volume 31 I selected radio, and the volume shot up to ear-splitting.
That was when the trunk crashed to the ground and all four tires deflated. Well, almost...