I recommend trying to do this with the following settings:
Race: Lv. 1 - The Snowfields
Character: My Avatar or Krystale
Board: Rare Board – High Top
"A" Rank reference time: 1'10"891
You need to get down the mountain as fast as possible while navigating through the gates at the same time. For every gate you miss, you will receive a 2 second penalty. Again, just keep replaying the first race until you memorize the locations. By the time I got my first "A" rank I was able to hit 31 of the 32 gates without too much trouble. Remember to pretty much lean forward the whole time for more speed and there are a couple of turns where you will need to make a sharp slow turn to get between the gates. Other than that it is straight ahead with some slight directional adjustments.