From what I had gathered in a little test, it seams like the game runs a point system behind the level up process.
Working like 8pts for first, 4 for 2nd, 2 for 3rd and 1 for 4th (from what it seams even last place gives points)
And it requires the same amount of points as the number of wins Famine posted, so it's like:
D > C 8pts
C > B 8pts
B > A 16pts
A > S 24pts
But I would like to test it further to see if all that is 100% accurate or not.
Also note that the number of laps don't affect the level up process.