Angular momentum proportions are based on the total width, height and length of the car. (x , y , z)
X: This value affects to steering and "barrel-rolling". If this value is very high, the car will roll sideways very slowly & smoothly, maybe like it had some helium in it. (Unlike in the first picture)
Y: This affects to barrel-rolling too, if you put a high value here.
Z: This affects mostly to steering. And if the value is too high here, and you drive down from a rooftop, the car won't lean forward when there's not anymore ground under the front wheels. (Second picture)