Class i array laver access violation

Jeg leger med classes i øjeblikket... jeg har nu lavet et array [1..5] of TLastvogn, som er en class. Men når jeg bruger en for-løkke i FormCreate'n laver den en access violation. Kode:

MainU:
---------------------------------------------

unit MainU;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ClassU, StdCtrls, Spin;

const
  AntalBiler = 5;

type
  TForm1 = class(TForm)
    Button1: TButton;
    Label1: TLabel;
    Label2: TLabel;
    SpinEdit1: TSpinEdit;
    Label3: TLabel;
    Edit1: TSpinEdit;
    procedure FormCreate(Sender: TObject);
    procedure Button1Click(Sender: TObject);
    procedure SpinEdit1Change(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  Lastvogn : TLastvogn;
  Lastbiler : array [1..AntalBiler] of TLastvogn;
  AktuelLastvogn : Integer;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
  i : Integer;
begin
  Lastvogn := TLastvogn.Create;
  Lastvogn := TLastvogn.Create;
  Lastvogn.KasseVaegt := 5;
  AktuelLastvogn := SpinEdit1.Value;

  for i := 1 to AntalBiler do
  begin
    Lastbiler[i].KasseVaegt := 5; // Her laver den en AccessViolation
    Lastbiler[i].AntalKasser := 0;
  end;
end;

procedure TForm1.Button1Click(Sender: TObject);
var
  tmp : Integer;
begin
  tmp := Edit1.Value;

  Lastvogn.AntalKasser := tmp;

  Label2.Caption := IntToStr(Lastvogn.Vaegt);
end;

procedure TForm1.SpinEdit1Change(Sender: TObject);
begin
  AktuelLastvogn := SpinEdit1.Value;
  Edit1.Value := Lastbiler[AktuelLastvogn].AntalKasser;
end;

end.

ClassU:
---------------------------------------------

unit ClassU;

interface

type
  TLastvogn = class(TObject)
    private
      FAntalKasser : Integer;
      FKasseVaegt : Integer;
      function GetVaegt : Integer;
    public
      property AntalKasser : Integer
        read FAntalKasser
        write FAntalKasser;
      property KasseVaegt : Integer
        read FKasseVaegt
        write FKasseVaegt;
      property Vaegt : Integer
        read GetVaegt;
    end;

implementation

function TLastvogn.GetVaegt : Integer;
begin
  Result := KasseVaegt * AntalKasser;
end;

end.