The M Coupé shares its 3.2 L Inline-6 with the M Roadster. The E86 Coupé features a fixed hard-top roof which yields additional torsional rigidity 24,000 lb·ft per degree of body twist on the coupe compared to 10,700 lb·ft per degree on the roadster. This additional rigidity improves driving dynamics and corner handling. The roof now features a ‘double bubble’ contour which serves as an aerodynamic aid and offers more headroom than the roadster with top closed. The coupe has a sleek fastback rear window that slopes down to an integrated spoiler shaped to deliver downforce to the rear axle at speed.
Over the Z4 E86 life cycle (2006–2008), only 12,819 Z4 coupés (E86) were produced worldwide