How do Grand Prix Ranking work?
Solution 1:
Similar to Mario Kart Wii, there is no definitive answer, as the game developers have not released this information. Star ranking appears to correlate the most with fast track times and good coin collection (though that may be because coins make you faster), but nothing out there is definitive.
It is certainly not random, however. Many players report getting 3 Stars on virtually all grand prix races every time they try them.