That really annoys me that that happens as it becomes hard to know what times you have to get to get 3 star rank with each character.
its not entirely based on time:
Mario Kart DS Formula (Revised to fit Wii standards)
Your GP rank is decided by 2 scores, your Championship Point (CP) and your Hidden Point (HP).
Everybody should be familiar with CP. It's the point given to you based on where you placed in each race:
1st: 15
2nd: 12
3rd: 10
4th: 8
5th: 7
6th: 6
7th: 5
8th: 4
9th: 3
10th: 2
11th: 1
12th: 0
HP is a score that is hidden from the player, and it's given base on how "well" you performed in the race. You start with 0 HP, and according to what you did, points are added or deducted from your HP.
ACTIONS THAT ADD HP:
-- Total Time for Each Race --
Each circuit has a preset time. You will be awarded HP depending on how much faster your time is from the preset time.
-- Lead Time --
HP is given for been in 1st place. The longer you are in 1st, the more HP you receive.
-- Rocket Boost/Start --
+25 HP for each successful Rocket Boost.
-- Mini-Turbo --
+2 HP for each successful mini-turbo.
-- Item Attack --
+5 HP for each successful attack using item.
--Tricks--
+? HP for each successful trick.
--Wheelies--
+? HP for each succesful wheelie.
ACTIONS THAT DEDUCT HP:
-- Off-Track Time --
HP is deducted for the amount of time you spend off the track. The longer you are off-track, the more HP you loss. Exceptions are when you are under the effect of star, mushroom, bullet pill, or ghost(Boo).
-- Hit a Wall --
-20 HP everytime you hit a wall.
-- Hit a Course Obstacle --
-30 HP everytime you hit a course obstacle (car, fireball, etc.).
-- Fall Off Track/ Pick Up by Lakitu--
-70 HP everytime you fall off track and get picked up by Lakitu.
----------------------
Rank
-- 60 CP: --
1000+ HP = 3-star (***)
700-999 HP = 2-star (**)
400-699 HP = 1-star (*)
200-399 HP = A
0-199 HP = B
negative HP = C
-- 52-59 CP: --
1000+ HP = 2-star (**)
700-999 HP = 1-star (*)
400-699 HP = A
200-399 HP = B
0-199 HP = C
negative HP = D
-- 47-51CP: --
1000+ HP = 1-star (*)
700-999 HP = A
400-699 HP = B
200-399 HP = C
0-199 HP = D
negative HP = E
-- 40-46CP: --
1000+ HP = A
700-999 HP = B
400-699 HP = C
200-399 HP = D
less than 200 HP = E
-- 0-39CP: --
1000+ HP = B
700-999 HP = C
400-699 HP = D
less than 400 HP = E