In the most basic movements, the car accelerate and brake at different rates. In the game the brake force is stronger.
The pivot point is at the front wheels, and the rotation force vary with the speed. I used a second degree polynomial curve :
(-(1/max_speed)*current_speed^2+current_speed)/(max_speed/4)
The resulting curve will be a float between 0 and 1. This value is a coefficient that will be multiplied with the real rotation speed. That mean the max rotation speed available is when we are in the middle point between the max speed and 0.
But there is a twist: on the second half of the curve I add a "high speed rotation" value to the coefficient (0.3 is an acceptable value). The value is then capped at one.
The final curve is a standard growing curve until the middle point, where it keep at its maximum value for a while and then drop slowly to stop at the high speed rotation value.
I hope this explanation will help you with your 3D car physics :)
If you have any questions or if I didn't explain well some things don't hesitate to ask !