Can't get a raycast suspension system to work properly.

Hey everyone. I am currently trying to get a raycast based suspension system off the ground and I just cant seem to figure out why my physics engine is going bananas. Here is a .gif of what is going on.

https://www.youtube.com/watch?v=kchI-AURdG8

Here is the code snippet:

 void Start()
 {
     car = this.gameObject.GetComponent<Rigidbody>();
     car.centerOfMass = new Vector3(0, -dropCOM, 0);
     RaycastHit fLRayHit;
     RaycastHit fRRayHit;
     RaycastHit rLRayHit;
     RaycastHit rRRayHit;
     if (Physics.Raycast(fLTire.position, -fLTire.up, out fLRayHit, susLength))
         fLPos1 = fLRayHit.distance;
     if (Physics.Raycast(fRTire.position, -fRTire.up, out fRRayHit, susLength))
         fRPos1 = fRRayHit.distance;
     if (Physics.Raycast(rLTire.position, -rLTire.up, out rLRayHit, susLength))
         rLPos1 = rLRayHit.distance;
     if (Physics.Raycast(rRTire.position, -rRTire.up, out rRRayHit, susLength))
         rRPos1 = rRRayHit.distance;
 }

 // Update is called once per frame
 void Update()
 {

 }

 void FixedUpdate()
 {
     RaycastHit ground;
     Ray groundCheck = new Ray(transform.position, -transform.up);

     if (Physics.Raycast(groundCheck, out ground, 10f, groundLayer))
     {
         gravityDir = ground.normal;
         Debug.Log(gravityDir);
         groundRot = ground.transform.rotation.x;
     }

     car.AddForce(gravityDir * gravityVal, ForceMode.Acceleration);

     RaycastHit fLRayHit;
     RaycastHit fRRayHit;
     RaycastHit rLRayHit;
     RaycastHit rRRayHit;

     if (Physics.Raycast(fLTire.position, -fLTire.up, out fLRayHit, susLength))
     {
         float fLPos2 = fLRayHit.distance;
         float velocity = (fLPos1 - fLPos2) / Time.deltaTime;
         float fLRatio = (susLength - fLRayHit.distance) / susLength;
         float susLift = fLRatio * susForce + velocity * susDamp;
         float lift = susLift;
         car.AddForceAtPosition(lift * fLTire.up, fLTire.position, ForceMode.Acceleration);
         fLPos1 = fLPos2;
     }

     if (Physics.Raycast(fRTire.position, -fRTire.up, out fRRayHit, susLength))
     {
         float fRPos2 = fRRayHit.distance;
         float velocity = (fRPos1 - fRPos2) / Time.deltaTime;
         float fRRatio = (susLength - fRRayHit.distance) / susLength;
         float susLift = fRRatio * susForce + velocity * susDamp;
         float lift = susLift;
         car.AddForceAtPosition(lift * fRTire.up, fRTire.position, ForceMode.Acceleration);
         fRPos1 = fRPos2;
     }

     if (Physics.Raycast(rLTire.position, -rLTire.up, out rLRayHit, susLength))
     {
         float rLPos2 = rLRayHit.distance;
         float velocity = (rLPos1 - rLPos2) / Time.deltaTime;
         float rLRatio = (susLength - rLRayHit.distance) / susLength;
         float susLift = rLRatio * susForce + velocity * susDamp;
         float lift = susLift;
         car.AddForceAtPosition(lift * rLTire.up, rLTire.position, ForceMode.Acceleration);
         rLPos1 = rLPos2;
     }

     if (Physics.Raycast(rRTire.position, -rRTire.up, out rRRayHit, susLength))
     {
         float rRPos2 = rRRayHit.distance;
         float velocity = (rRPos1 - rRPos2) / Time.deltaTime;
         float rRRatio = (susLength - rRRayHit.distance) / susLength;
         float susLift = rRRatio * susForce + velocity * susDamp;
         float lift = susLift;
         car.AddForceAtPosition(lift * rRTire.up, rRTire.position, ForceMode.Acceleration);
         rRPos1 = rRPos2;
     }

     inputDevice = InputManager.ActiveDevice;

     float deadzone = deadZone;
     stickInput = new Vector2(inputDevice.LeftStickX, inputDevice.LeftStickY);
     if (stickInput.magnitude < deadzone)
         stickInput = Vector2.zero;
     else
         stickInput = stickInput.normalized * ((stickInput.magnitude - deadzone) / (1 - deadzone));
 }

I want this to just act like a normal suspension system. Any help would be greatly appreciated. I am still fairly new to this stuff.

The reason for the custom gravity situation is that I want the vehicle to be able to drive on the walls and ceiling.

Thanks