for what i understand (and i did something that works more or less correctly), what you are looking for is located in the "place" method of the car class
By default, the car is located 10 upper than its last position with the following call:
translate(0, -10, 0);
Then, you have those lines :
float rightFrontHeight=ground.calcMinDistance(rightFront.getTransformedCenter(), dropDown, 4*30);
float rightRearHeight=ground.calcMinDistance(rightRear.getTransformedCenter(), dropDown, 4*30);
float leftFrontHeight=ground.calcMinDistance(leftFront.getTransformedCenter(), dropDown, 4*30);
float leftRearHeight=ground.calcMinDistance(leftRear.getTransformedCenter(), dropDown, 4*30);
Each of the value obtained determine the distance between one of the wheel of the car and the ground...
The rest of the place method will consist in dropping down the car until each wheel collide with the ground... (as expressed by the lines you gave before). If i remenber, the angle will be used to orientate the body of the car but not so sure of that... Egon will probably complete it with his "magical expanations"