For this test, two meshes objects have been added to the
setup, and two Empties.
The wheels are more independent and their slope is affected by the weight of the car.
The two Empties are not really necessary if you need only automated animation, but they are very useful to allow an adjustment of the wheels slope, espescially when the car takes off, like when jumping over the broken bridge.
By moving the front and rear empties along their Local Z axis and inserting few Loc keyframes, it is easy to simulate the wheels fall, due to gravity.