The first generation of the BMW Z4 consists of the BMW E85 (roadster version) and BMW E86 (coupe version) sports cars. The E85/E86 generation was produced from 2002 to 2008. The E85/E86 replaced the Z3 and is the third model in the BMW Z Series. Initial models were in the roadster (E85) body style, with the coupé (E86) body style being added in 2006. In February 2009, the BMW Z4 (E89) began production as the successor to the E85/E86.

The E85 was designed by Danish BMW-designer Anders Warming from mid-1998 to the summer of 1999.[citation needed] The coupe models were designed by Tomasz Sycha.[3] The E85 designs were frozen on March 1, 2000.[4] The Z4 was introduced at the Paris Motor Show in 2002,[5] and North American models went on sale in November of the same year (as the 2003 model year). European sales began in March 2003.[6]

Initial models consisted of the roadster body style powered by a 2.5L or 3.0L 6-cylinder engine

Roadster (E85)
The Z4 Roadster was launched in 2002 with the 2.5i and 3.0i six-cylinder models.[7] Transmission choices were a five-speed manual, six-speed manual, five-speed automatic and a six-speed SMG-II automated manual transmission.[8]

A four-cylinder model, the Z4 2.0i Roadster, was introduced for the European market in May 2005.

The drag coefficient is maximum of Cd=0.35

Coupé (E86)

Z4 Coupé (rear view)
BMW unveiled a concept coupé version of the Z4 at the 2005 Frankfurt Motor Show.[10] The design of the Z4 and Z4 coupé has variously been ascribed to Anders Warming, Chris Bangle, the controversial former BMW Head of Design, and Adrian van Hooydonk, former BMW chief designer,[11][12] and BMW designer Tomasz Sycha. The design was approved in Summer of 2004 and frozen in December 2004. The company announced in 2005 that the two-door coupé would be available for production including the return of the M Coupé. The production car was introduced at the New York Auto Show in April 2006 and was available for sale in late May 2006.[13]

Thanks to its hatch design, the Z4 Coupé offers 10.1 cu ft (0.29 m3) of trunk space,[14] compared with 8.5 cu ft (0.24 m3) for the roadster.[15]

The Coupe's fixed roof increases torsional rigidity, resulting in a stiffness of 32,000 N⋅m (24,000 lb⋅ft) per degree of body twist on the coupe (compared to 14,500 N⋅m (10,700 lb⋅ft) per degree on the roadster), which improves turn-in and overall handling response.[16] The roof has a "double-bubble" contour which serves as an aerodynamic aid and offers more headroom than the roadster with the soft top closed. The Coupé has a sleek fastback rear window that slopes down to an integrated spoiler which is shaped to deliver downforce to the rear axle at high-speed.

The model range for the Coupé was more limited than the roadster, and consisted of the six-cylinder 3.0si and Z4 M model only.[17][18] Transmission choices were a 6-speed manual and a 6-speed automatic with shift paddles mounted on the steering column

Compared with its Z3 predecessor, the Z4 is larger and has a stiffer chassis.[19] As per the Z3, the front suspension is a Macpherson strut design. The rear suspension uses a multi-link design, instead of the semi-trailing design used by the Z3. Some reviewers have criticised the ride quality for being too harsh, and observed excessive bump steer from the rear suspension.[20]

The Z4 used lightweight materials to offset the increased weight over the smaller Z3, such as an aluminum hood and suspension components, magnesium roof frame. Run-flat tires removed the need for a spare tire, which reduces weight and allows for a larger trunk

The 6-cylinder engines included all-alloy construction, variable valve timing (double-VANOS), and throttle by wire. Safety technology included four-wheel disc brakes and electronic stability control, incorporating ABS and traction control.

An optional "Sport Package" included added stiffer and lower suspension, 18 inch wheels, and sport tuned electronic steering, throttle and shift parameters ("Dynamic Driving Control").[22]

Electric power steering replaced the traditional hydraulic power steering used by the Z3.[23][24] The power assist is speed-sensitive, allowing for easier maneuvering at low speeds. The steering has been criticised for lacking feedback.[25] However, the Z4 M uses hydraulic power steering, and has been judged as having a more direct and communicative feel to the steering.[26]

In 2002 a 6-speed SMG gearbox was offered as an option on the 2.5 and 3.0 roadsters