CarMovement.cs

using UnityEngine;

public class CarMovement : MonoBehaviour {

	public WheelCollider rl = null;
	public WheelCollider rr = null;
	public WheelCollider fl = null;
	public WheelCollider fr = null;

	public float torque = 10.0f;
	public float brakeStrength = 5.0f;
	public float steering = 10.0f;

	void Update () {

		float acceleration = Input.GetAxis ("Vertical") * torque;
		float steer = Input.GetAxis ("Horizontal");

		Debug.Log (acceleration);

		rl.motorTorque = acceleration;
		rr.motorTorque = acceleration;

		fl.steerAngle = steer * steering;
		fr.steerAngle = steer * steering;

		/*if (acceleration > 0.0f) {
			rl.motorTorque = acceleration * torque;
			rr.motorTorque = acceleration * torque;
		} else if (acceleration < 0.0f) {
			rl.brakeTorque = brakeStrength;
			rr.brakeTorque = brakeStrength;
		} else {
			rl.brakeTorque = 0;
			rr.brakeTorque = 0;
		}*/

	}
}