X rotation locked with character controller

I have a car that won't tilt downwards when going down a hill. The back bumper just rubs along the ground. So basically the x and z are locked. This is the code I use for moving the car:

 using UnityEngine;
 using System.Collections;
 
 public class CarControl : MonoBehaviour {
 
     public Transform flw;
 
     public Transform frw;
 
     public Transform blw;
 
     public Transform brw;
 
     CharacterController cc;
 
     Quaternion leftTurn = new Quaternion(0, 75, 0, 25);
 
     Quaternion rightTurn = new Quaternion(0, -75, 0, 25);
 
     Quaternion noRotation = new Quaternion(0, 0, 0, 0);
 
     public float topSpeed;
 
     float currentSpeed;
 
     public float acceleration;
 
     Vector3 direction;
 
     // Use this for initialization
     void Start () {
     
         cc = GetComponent<CharacterController> ();
     }
     
     // Update is called once per frame
     void Update () {
 
         direction = transform.rotation * new Vector3 (0, 0, Input.GetAxis ("Vertical"));
     
         if (currentSpeed == 0) {
             //Nothing.
         } else if (currentSpeed > 0) {
             currentSpeed -= 0.05f;
         } else if (currentSpeed < 0) {
             currentSpeed += 0.05f;
         }
 
         if (Input.GetKey ("a") && currentSpeed > 0.5) {
             flw.rotation = leftTurn;
             frw.rotation = leftTurn;
             cc.transform.Rotate(new Vector3(0, -2, 0));
         } else {
             flw.rotation = noRotation;
             frw.rotation = noRotation;
         }
         if (Input.GetKey("d") && currentSpeed > 0.5) {
             flw.rotation = rightTurn;
             frw.rotation = rightTurn;
             cc.transform.Rotate(new Vector3(0, 2, 0));
         }
 
         if (Input.GetKey ("w") || Input.GetKey("s")) {
 
             if(currentSpeed <= topSpeed){
                 currentSpeed += acceleration;
             }
 
             if(Input.GetKey("space") && currentSpeed > 0){
                 currentSpeed -= 0.1f;
             }
 
         }
     }
 
     void FixedUpdate(){
         if (currentSpeed > 0.1) {
             cc.SimpleMove(direction * currentSpeed);
         }
         }
 }