SrcWheel.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class ScrWheel : MonoBehaviour {
    private Rigidbody rb;

    public bool wheelFrontLeft;
    public bool wheelFrontRight;
    public bool wheelRearLeft;
    public bool wheelRearRight;

    [Header("Suspension")]
    public float restLength;
    public float springTravel;
    public float springStiffness;
    public float damperStiffness;

    private float minLength;
    private float maxLength;
    private float lastLength;
    private float springLength;
    private float springVelocity;
    private float springForce;
    private float damperForce;

    [Header("Wheel")]
    public float steerAngle;
    public float steerTime;

    private Vector3 suspensionForce;
    private Vector3 wheelVelocityLS; // Local Space
    private float Fx;
    private float Fy;
    private float wheelAngle;

    [Header("Wheel")]
    public float wheelRadius;

    void Start() {
        rb = transform.root.GetComponent<Rigidbody>();

        minLength = restLength - springTravel;
        maxLength = restLength + springTravel;
    }

    void Update() {
        wheelAngle = Mathf.Lerp(wheelAngle, steerAngle, steerTime * Time.deltaTime);
        //transform.localRotation = Quaternion.Euler(transform.localRotation.x, transform.localRotation.y + steerAngle, transform.localRotation.z);
        transform.localRotation = Quaternion.Euler(Vector3.up * wheelAngle);

        Debug.DrawRay(transform.position, -transform.up * (springLength + wheelRadius), Color.green);
    }

    void FixedUpdate() {
        RaycastHit hit = new RaycastHit();
        if (Physics.Raycast(transform.position, -transform.up, out hit, maxLength + wheelRadius)) {
            lastLength = springLength;
            springLength = hit.distance - wheelRadius;
            springLength = Mathf.Clamp(springLength, minLength, maxLength);
            springVelocity = (lastLength - springLength) / Time.fixedDeltaTime;
            springForce = springStiffness * (restLength - springLength);
            damperForce = damperStiffness * springVelocity;

            suspensionForce = (springForce + damperForce) * transform.up;

            wheelVelocityLS = transform.InverseTransformDirection(rb.GetPointVelocity(hit.point));
            Fx = Input.GetAxis("Vertical") * 0.5f * springForce;
            Fy = wheelVelocityLS.x * springForce;

            rb.AddForceAtPosition(suspensionForce + (Fx * transform.forward) + (Fy * -transform.right), hit.point);
        }

    }
}