How to get car to reverse using motorTorque/WheelColliders?

My car doesn't reverse, I've tried adding an else if for when the velocity is zero and s is being held down that motorTorque = -torque but this does nothing. Here is my code:

 public class CarMovement : MonoBehaviour
 {
     public GameObject backLeftWheel, backRightWheel, frontLeftWheel, frontRightWheel;
     WheelCollider blWheel, brWheel,flWheel,frWheel;
     public Rigidbody car;
     public float carVelocity;
     // Start is called before the first frame update
     public float torque, brakeTorque, maxSpeed, highSpeedSteeringAngle, lowSpeedSteeringAngle;
 
     public Vector3 resetPosition;
     public Quaternion resetRotation;
     void Start()
     {
         car.centerOfMass = new Vector3 (0.0f, -0.75f, .35f);
         blWheel = backLeftWheel.GetComponent<WheelCollider> ();
         brWheel = backRightWheel.GetComponent<WheelCollider> ();
         flWheel = frontLeftWheel.GetComponent<WheelCollider>();
         frWheel = frontRightWheel.GetComponent<WheelCollider> ();
     }
 
     // Update is called once per frame
     void Update()
     {
          carVelocity = this.gameObject.GetComponent<Rigidbody> ().velocity.magnitude;
         if (Input.GetAxis ("Vertical") > 0 && carVelocity < maxSpeed) {
             blWheel.motorTorque = torque;
             brWheel.motorTorque = torque;
         } else if (Input.GetAxis ("Vertical") < 0 && carVelocity > 0) {
             blWheel.brakeTorque = brakeTorque;
             brWheel.brakeTorque = brakeTorque;
             flWheel.brakeTorque = brakeTorque;
             frWheel.brakeTorque = brakeTorque;
         } 
         else
         {
             blWheel.brakeTorque = 0;
             brWheel.brakeTorque = 0;
             flWheel.brakeTorque = 0;
             frWheel.brakeTorque = 0;
             blWheel.motorTorque = 0;
             brWheel.motorTorque = 0;
         }
         if (Input.GetAxis ("Horizontal") != 0) {
             flWheel.steerAngle = lowSpeedSteeringAngle*Input.GetAxis ("Horizontal");
             frWheel.steerAngle = lowSpeedSteeringAngle*Input.GetAxis ("Horizontal");
         } 
 
         if (this.transform.position.y < -1f) {
             resetCar ();
         }
     }