Sonic Riders Zero Gravity stunt ranks

Time for some nostalgic trip to the PS2 era. Basically the stunt ranks depending on how perfect you press the X button before you do a stunt. Do it too early or too late, and you'll get C which doesn't increase your score.

X
This is the rank that gives the biggest amount of gravity points. The X rank is only awarded if you: The latter happened when I jumped on a ramp in Meteor Tech Sparkworks. This seems to be extremely rare as subsequent jumps are usually counted as SS rank.
 * Do an S-ranked stunt for your first stunt in a level (subsequent jumps will either only reward you an SS or S rank).
 * Press the X button near the edge of a ramp (extremely rare).

X-ranked jumps usually has a "wind" effect when you do the stunt.

SS
The second highest rank. The SS rank can be awarded by pressing the X button near the edge of a ramp, while doing subsequent jumps. At first, it is an S rank, but the letter S will spin and turn into SS.

S
The third highest rank which can be awarded by pressing the X button a bit farther to the edge, but not too far so that you'll miss it.

AA
Almost the same as A, but can be earned when jumping a bit closer to the edge, but not that close.

A
This can be done by pressing the X button while you're at low speeds, such as 90 or 100, or you can just time it so that you jump on the middle of the ramp.

BB
Almost the same as B, but can be earned when jumping a bit later than the B rank.

B
You can get this rank by pressing the X button as soon as the button pops up on the screen. This gives you the smallest amount of GP.

C
This rank won't give you any gravity points since it counts as a failed jump. The character will also say things like "No!" instead, and they'll lose the grip with their hoverboard for a few seconds. It is untested whether or not doing C-ranked stunt will award you a B rank when you do it on first level jump, but probably it won't since it counts as a penalty.

Trivia

 * It is unknown why would Sega decide to use ranks like SS, AA, and BB instead of S+, A+, and B+, which are more logical to the school grading.
 * There are no XX and CC ranks, probably because the former would be impossible to get without hacking and the latter would look somewhat awkward since the character was meant to respond negatively when they get the C rank.