OK. Good news and bad news.
Good news: I found the location that controls the player car's virtual size (shown by the shadow. see the attached screenshots) which can be used to fix the "sinking in the ground" problem.
000011B7-000011C3The game reads it as a distance (in
x,y,z) from the center of the car (measured in degrees?).
000011B8-000011BA = virtual size of car from center horizontally or
x (How wide the virtual car is)
000011BC-000011BE = virtual size of car from center vertically or
y (this is what causes the "sinking in the ground" or "hovering above the ground" effects)
000011C0-000011C2 = virtual size of car from center lengthwise or
z (How long the virtual car is)
NOTE: The values below are to be left untouched. They tell the game where the x values begin/end, where the y values begin/end and where the z values begin/end. If you change these values, expect insane results in-game (and by insane I don't mean cool).
000011B7 = X (always set to hexadecimal 3F)
000011BB = Y (always set to hexadecimal 3F)
000011BF = Z (always set to hexadecimal 3F)
000011C3: Additionally this is always set to hexadecimal 40.
Bad news: if you change your car for another one (via hex editing the .gst file) and you find that it is sinking in the ground (or hovering above it) it will be very complicated to center that car on the road. The only workaround I found so far is to copy the data of a player car from line 00001170 and lines 000011B7-000011C3 of another .gst file that contains the car you want to drive, and replace the same lines in the data of the .gst file you are using. Additionally, you can copy the data from the AI racers in the same or another .gst file and replace your data. That work's fine, too. Just remember to change line 0000117C (defines AI type) from 02 (AI racer) to 01 (Player racer)(or 09 if you are in Hot Pursuit and want to be the cop). The game WILL crash if this isn't done.
Just on a sidenote if you copy all the data from lines 00001170-000011C3 you will retain the transmission used, the convertible option, and the car's color.
Hope this helps.