So, in Forza 4 and Forza Horizon the PI was like this: F, E, D, C, B, A, S, R3, R2, R1, X (FH4 Only)
Yet I have seen in Forza Horizon play throughs a new rank, S2, at 998, the max rating for R1 in Forza 4 before it becomes an X class.
So, what are the differences?
See this:
http://forums.forza.net/turn10_postsm440102_posts.aspx#post_440102