Why did you deduct the weight of permanent fittings like the towbar and side steps, etc.? In doing so, you have determined the ex-works weight but not the actual current kerbweight of the car. Any feature which is permanently added to the vehicle after it leaves the factory automatically changes the kerbweight. Contrary to GVW and gross train weight, which are not variable amounts but absolute limits specified by the manufacturer, the kerbweight is a variable which can be changed at any time by technical modifications to the vehicle.