Max allowable width with out notification is 3m, which isn't much overhang as trucks are allowed up to a max width of 2.55m (not counting mirrors) or 2.6m for refrigerated vehicles. You are allowed a 1.8m rear overhang, but if it is a rigid vehicle you must still adhere to the rule that the rear of the load must be no more than 60% of the wheelbase to the rear of the rear axle.