BMW has a long, if sporadic, history of making roadster sports cars. It made the 328 for four years from 1936, two decades later it made the 507 for four years, and then three decades later it made the Z1 for four years until 1991. In their time these cars were lauded by the motoring press for offering something different and more advanced than the competition. But they were expensive and as a result sold in small numbers, less than 9000 units in total.
The Z3 launched in 1995 changed all that. The Z3 was designed to compete at the top end of the new sports car market sector defined by the Mazda MX5/Miata, and sold at more than 50 times the rate of its predecessors.
Given the Z3’s success it might have been expected that BMW would replace it with an evolutionary product, but its successor, the Z4, was developed at the outset from a clean sheet of paper.
The Z4’s task was to maintain the high level of sales success of the Z3, but also continue its move up-market to compete directly with the Porsche Boxster, Mercedes SLK, Honda S2000, Chevrolet Corvette and forthcoming Nissan 350Z.
And it had to reassert BMW’s ‘ultimate driving machine’ identity and heritage of building advanced sports cars after the uninspiring handling and performance of the Z3, and its retro design identity.
In 1998 the design group in Munich began making Z4 ‘mules’, based on cut-and-shut Z3s, to develop a strong front engine roadster proportion, similar to sports cars from the class above the Z4, like the Mercedes SL, Jaguar XK8, Maserati Spider and its short lived sibling, the Z8. This traditional sports car proportion would distinguish the Z4 from similarly priced but more ‘cab-forward’ proportioned and less focused sports cars, such as the front wheel drive Audi TT and Alfa Romeo Spider, although perhaps not so much from cars like the Honda S2000 and Chevrolet Corvette. This ‘cab-backward’ proportion was also seen to be a natural progression of the Z3’s long nosed look, which would help appease existing Z3 owners who might otherwise have found the Z4 design too much of a departure. Fundamentally, it ensured that the Z4 might never be accused of being a 'hairdresser’s car’.
Once the core proportions of the package had been created, sketch development work began in both the Munich and California studios. Within Designworks (the Californian studio) three of the designers worked on Z4 proposals and at the larger Munich studio approximately 15 designers were engaged at this initial stage.
After three months of sketch development, four exterior and four interior design proposals from Munich and one exterior and one interior design proposal from California were selected to progress into 40% scale clay models. Working on each exterior model was a team comprising one designer, one design engineer (studio engineer) and four to five modelers. On each interior model were one interior designer, one color and trim designer, one design engineer, one ergonomist and two to three modelers.
At the beginning of 1999, three Munich exterior design proposals and the one Californian proposal were chosen for progression into full size clays, whilst two of the Munich based interior proposals were chosen for development into full size models.
With its roof down, a roadster’s interior becomes part of its exterior, so it was particularly important that there was an empathy between interior and exterior design development, afforded in part at BMW by its designers doing both exterior and interior work (the Z4 exterior designer was also responsible for the X-coupe concept car interior). Ultimately the selected interior and exterior models were refined as full size clays sitting adjacent to each other in the same studio, designers moving from one model to the other to ensure the final design worked as a whole.
In Summer 1999 the Designworks proposal for the Z4 exterior by Anders Warming and the Munich based interior proposal from Oliver Sieghart were selected as the designs to progress to production.
Although little is known about the proposals not chosen for production, Warming’s exterior design has possibly the most unique surfacing of any production car today and he cites in particular his reliance on the modelers and his own ‘hands-on’ approach to clay modeling as having been critical to its development. This ‘flame surfacing’ is more subtle and more controlled than that of Chris Chapman’s X-Coupe concept car shown in Detroit 2001, although significantly it should be noted that the Z4 predates the X-Coupe in its design inception.
Unusually sharp edges define the boundaries of surface areas, which in the flanks of the car move through convex and concave almost as if moving, and give credence to the term ‘flame surfacing’. This, according to Warming, ‘reflects the dynamic performance below the surface and thus emphasizes the characteristics of the car and the (aspired) personality of its drivers’.
The lower belt line echoes classic sports cars such as the big Healey and BMW’s own 507 as it arcs back from the front lamps through the wings and down into the doors to abruptly whip back up and around to define the rear wing of the car, accentuating the ‘cab-backward’ proportions of the car as it does so.
But otherwise the detailing of the car shows innovative new interpretations of BMW’s design signifiers, such as the recessed, more voluptuous double kidney grill and roundel logo integrated with the side repeater, and wholly new design elements such as the body color break running through the rear lamps.
The interior of the car has an architecture closely related to the 7-series, with a strong horizontal theme running across the IP replacing the traditional BMW driver focused feel. Floating cowled instrumentation and a clearly sporting, if perhaps rather retro, steering wheel signify this as a new sports car interior for BMW.
Exterior and interior designs were refined in Munich from summer 1999 to summer 2000 when they were slowly frozen as deadlines for the manufacturing of components were reached. It was then that digital design tools were used most, with the final design being digitized for production. Up until this point this particular BMW exterior design had been developed using only traditional methods (except when resizing the model to full size), with the interior using digital design just for small elements.
Exterior designer, Anders Warming, describes the Z4 design development as a ‘project of passion’ that enthused all of the many people involved. Although identifiable as the designer responsible for the exterior design, as was Oliver Sieghart for the interior, Anders worked with proportions developed by the team, with modelers in America and Germany and with frequent input from Design Director Chris Bangle and other designers. As such, the Z4 design development is a story of the creation of a new BMW sports car and also of impassioned individuals working together as a team.