you also calculate that formula off the factory issued weight, of the sedan bodied variant, so its 770kg's ive gone over this so many times, by the rta it is not engineerable but there is probably exceptions to the ruel, i reckon the rta and police will catch on soon. the police around my area know a certain dodgy engineer and if u are pulled up and the cops see's a certificate from this guy they still book you, it happened to a mate of mine.