Axle.cs

using System;
using UnityEngine;

// ReSharper disable once CheckNamespace
namespace MotherTruckers.Vehicle
{
    [Serializable]
    public class Axle
    {
        public WheelCollider LeftWheel;
        public WheelCollider RightWheel;
        public bool IsMotor;
        public bool IsSteering;
    }
}

VehicleController.cs

using UnityEngine;
using System.Collections.Generic;
using BeardedManStudios.Network;

// ReSharper disable once CheckNamespace
namespace MotherTruckers.Vehicle
{
    [RequireComponent(typeof(Rigidbody))]
    public class VehicleController : NetworkedMonoBehavior
    {
        public bool Controllable = true;

        public List<Axle> Axles;
        public float MaxTorque = 400f;
        public float MaxAngle = 30f;
        public float SteeringSpeed = 1f;

        public bool UseCustomCenterOfMass = false;
        public Transform CenterOfMass;

        private float TargetSteeringAngle = 0f;

        private Rigidbody _rigidbody;
        private Transform _transform;

        public void Awake()
        {
            this._rigidbody = this.GetComponent<Rigidbody>();
            this._transform = this.GetComponent<Transform>();

            if (this.UseCustomCenterOfMass)
                this._rigidbody.centerOfMass = this.CenterOfMass.localPosition;
        }

        public void FixedUpdate()
        {
            if (this.IsOwner)
                this.ProcessControls();

            if (!this.IsOwner)
                this._rigidbody.isKinematic = true;
        }

        public void Update()
        {
            if (this.IsOwner)
                this._transform.FindChild("Cameras").gameObject.SetActive(true);

            foreach (var axle in this.Axles)
            {
                this.VisualPosition(axle.LeftWheel);
                this.VisualPosition(axle.RightWheel);
            }
        }

        protected void ProcessControls()
        {
            if (!this.Controllable)
                return;

            var torque = this.MaxTorque * Input.GetAxis("Vertical");
            var steering = this.MaxAngle * Input.GetAxis("Horizontal");

            foreach (var axle in this.Axles)
            {
                if (axle.IsSteering)
                    this.Steering(axle, steering);

                if (axle.IsMotor)
                    this.Torque(axle, torque);
            }
        }

        protected void Steering(Axle axle, float amount)
        {
            axle.LeftWheel.steerAngle = amount;
            axle.RightWheel.steerAngle = amount;
        }

        protected void Torque(Axle axle, float amount)
        {
            axle.LeftWheel.motorTorque = amount;
            axle.RightWheel.motorTorque = amount;
        }

        protected void VisualPosition(WheelCollider c)
        {
            Transform wheelTransform = c.gameObject.GetComponent<Transform>().GetChild(0);
            Vector3 pos;
            Quaternion rot;
            c.GetWorldPose(out pos, out rot);
            wheelTransform.position = pos;
            wheelTransform.rotation = rot;
        }
    }
}