Manipulate Car Controls

I am using the standard unity car asset but cannot figure out how to modify it to my needs. Instead of using WASD to move the car, I want to move it by telling the script the distance to go and how fast. One of the two scripts attached below is for the car's physics movement and the other, CarUserController, is the script I am using to control it via buttons. I just need help getting the car to follow the variables created because the two scripts don't want to work together! As well as possibly getting the controls to instead of rotate the front two wheels when steering, to rotate the entire car by maybe inverting one side. I have not had much luck so any help is appreciated!

 

To clarify, I want to control the speed and distance in which the car moves, as well as change the steering to a tank type of movement

 

Anyone? Even a place to start would be helpful thanks