Car physics problem

Working on some basic suspension physics and I've run into an issue in which my car floats when in contact with the ground.

Here's my code, anyone have any insight?

 using UnityEngine;
 using System.Collections;
 
 public class suspensionPhys : MonoBehaviour {
 
     public Rigidbody rb;
     public GameObject carObj;
     public carPhys carScript;
 
     [Header("Suspension")]
     public float springForce;
     public float damperForce;
     public float springConstant;
     public float damperConstant;
     public float restLength;
 
     private float previousLength;
     private float currentLength;
     private float springVelocity;
 
     // Use this for initialization
     void Start () {
         rb = carObj.transform.GetComponent<Rigidbody>();
         carScript = carObj.GetComponent<carPhys>();
     }
 
     // Update is called once per frame
     void FixedUpdate () {
         RaycastHit hit;
         if (Physics.Raycast(transform.position, -transform.up, out hit, restLength + carScript.wheelRadius)) {
             previousLength = currentLength;
             currentLength = restLength - (hit.distance - carScript.wheelRadius);
             springVelocity = (currentLength - previousLength) / Time.fixedDeltaTime;
             springForce = springConstant * currentLength;
             damperForce = damperConstant * springVelocity;
 
             rb.AddForceAtPosition(transform.up * (springForce + damperForce), transform.position);
         }
     }
 }