NOT even BMW can produce a coupe-convertible replacement for separate roadster and coupe models without gaining weight. Unsurprisingly, the result is a second-generation Z4 that is larger, slower, considerably more expensive and, in most cases, less fuel-efficient than its predecessor. On the flip side is a greater level of safety, security and refinement, more luggage space (at least with the roof up) and new technologies such as iDrive and BMW’s cracking twin-turbo six, which is an additional variant but in effect, for now, replaces the Z4 M Roadster and Coupe. Only time will tell if Australians will warm to the considerably more grown-up Z4.