What makes the extra music layer start playing in Mario Kart 7?

Solution 1:

There are two extra requirements:

  • Speed. You have to maintain a certain forward velocity for the extra beat to play. I'm not sure what the exact number is, but it's higher than what's possible during a 50cc race, so you can only hear it in 100cc and above.
  • Separation. You have to maintain a certain distance between yourself and the 2nd-place racer. It would be hard to measure this without looking at the game's code.