The BMW Z4 is a rear-wheel drive sports car by the German automaker BMW, known as the E85 in roadster form and E86 in coupe form. Production started in 2002, and thus replaced the BMW Z3. The design addresses many criticisms of the Z3; the Z4 is larger, more powerful, and has a significantly stiffer chassis. It is built in Spartanburg, South Carolina. Initially, the Z4 was available only as a roadster, but in 2006 a coupé version was officially launched.
The Z4 was designed by Chris Bangle and began the controversy over his "flame surfacing" design and aggressive styling choices, which can also be seen on most modern BMW cars, most noticeably the 7 Series and 5 Series. As of 2006, the entire BMW car line, including the BMW 3 Series, had incorporated Chris Bangle's design theme.
The Z4 features a strut type front suspension like its precessor, the Z3. The rear suspension, however is considerably different from that of the Z3, which was based on that of the E30 BMW 3 Series. Instead of a semi-trailing arm suspension, the Z4 uses a more advanced multi-link suspension.
The Z4 offers a choice of four straight-six motors: A 2.2 L, a 2.5 L, a 3.0 L, and a 3.2 L. All are variants of the BMW M54 engine. In the European market, a 2.0 L straight-4 is also offered.
The 2.2 L, 120 kW (170 bhp) version can reach 100 km/h in 7.7 s, but is not sold in the United States.
The 2.5 L engine produces 141 kW (192 bhp) at 6000 rpm. BMW claims a 6.8 s time to 100 km/h (62 mph) with a manual transmission. It weighs 1,335 kg (2,932 lb) with a manual transmission—30 kg (66 lb) lighter than the 3.0 L version, but still heavier than the 2.5 L Z3's weight of 1315 kg (2899 lb).
The 3.0 L, 170 kW (231 bhp) (at 5900 rpm) straight six has a claimed time to 100 km/h (62 mph) of 5.9 s.
The 3.2 L motor produces 246 kW (330 bhp) at 7900 rpm and (262 lb-ft) of torque at (4900 rpm)
Five-speed manual gearboxes are standard on all models except the 3.0 L and the M Roadster, which has a 6-speed Getrag. 5-speed automatic are available on all cars. The M Roadster shares its 6-speed Getrag 217 manual gearbox with the M3. 
A Sport package is also available, which adds stiffer and lower suspension, larger wheels with run-flat tires, and Dynamic Driving control, BMW's Vehicle Stability Control system.
2006-2007 Z4 3.0si
2006-2007 Z4 3.0si
In 2006, BMW updated the Z4 line by installing its new N52 I-6 engines. In the 3.0si, this engine makes 255 bhp and 220 lb-ft of torque. The N52 features magnesium block construction and BMW's Valvetronic variable valve timing system. Although the new engines represent a modest upgrade in peak power over the M54, they are considerably more powerful through the middle of the rev range, and also improve fuel economy noticeably. A final benefit of the N52 engines (the lightest production 6-cylinder engines in the world) is that they improve handling and turn-in due the the decreased weight over the nose of the car. This is particularly noticeable when compared to the Z4 M, which continues with the heavier S54 iron block engine.
In addition to the powertrain updates, BMW made mild revisions to the styling of the Z4, added several electronic features, and increased the brake size on the 3.0si models.