As the new BMW 3 Series Sedan prepares for its world premiere, the next generation of the sports sedan is entering the final phase of an extensive programme of testing that every new BMW model must go through as part of its pre-production development.
Here, the full range of stresses and strains a car will encounter over many years of everyday driving are reproduced in concentrated form. From extended periods driving flat out to endless stop-start traffic, sub-zero temperatures to searing heat, twisty country roads and high-speed autobahns to pothole-infested tracks, ice and snow to gravel and desert sand, the prototypes sent through the test programme for the new BMW 3 Series Sedan have experienced everything their production equivalents will come across in everyday life.
To prevent curious onlookers from clocking too many details of the new BMW 3 Series Sedan’s design, every prototype is carefully clad in a disguise before it heads out onto public roads. In the basement of BMW’s Research and Innovation Centre (FIZ) in Munich, pre-production vehicles are kitted out with a made-to-measure and confusingly patterned cloak of camouflage. Applying the black-and-white wrap requires an expert hand and takes a whole working day to complete.
Then comes the plastic cladding, which distorts the lines and surfaces of the car. The light units, sections of the window surfaces and, of course, the brand badges also get a layer of sticky camouflage. The interior needs to be hidden from sight as well. To this end, the cockpit is “curtained off” with black matting, which the test engineers partially remove at the start of testing and then painstakingly replace at every pause in proceedings – so that no prying eyes can spot or even get a photograph of the displays and controls.
Long before the first test runs on public roads, the development process sees each new model taken into the company’s own testing facilities. In the initial phase of the programme, computer simulations help to set important areas of the car off on the right path. Here, the testing programme, which is still purely digital at this stage, involves simulating more than 12,000 driving manoeuvres (from lane changes to cornering and roundabout driving to dynamic acceleration and braking) using a computer-generated vehicle model, with the sole aim of determining and optimising its dynamic properties.
On the basis of the knowledge gained here, development mules are made consisting of just a body and chassis. On the kinematics compliance test bench they are fixed into a test assembly and sent on virtual test drives. A variety of road conditions can be faithfully reproduced on this test rig, from cobblestones to the Nürburgring’s Nordschleife circuit, so the rigidity of the body structure or the susceptibility to vibrations of axle constructions can be properly inspected.
Optimisation of aerodynamics and passive safety also takes place largely behind closed doors. At the BMW Group’s Aerodynamic Test Centre in Munich, full-size vehicle models, prototypes and production vehicles are tested using precise reproduction of real-life airflow conditions on the road.
At the centre’s wind tunnel, the new BMW 3 Series Sedan has been given the detailed touches required to bring its drag coefficient down to 0.23. The key factors here are not only how the car manipulates the airflow, the ideal channelling of air around the underbody and the optimisation of the spoiler lip at the rear of the body, but also details such as combinations of wheels and tyres.
The introduction of the WLTP fuel consumption testing procedure has meant all the wheel variants available for a particular model have to be put through an extensive aerodynamics test. Every variant is checked to establish how the wheel design and tyre size impact on the aerodynamic characteristics of the new BMW 3 Series Sedan and therefore its fuel consumption and emissions.
The proving grounds at Aschheim, a few miles north-east of the development centre in Munich, provides the venue for undisturbed dynamic testing. It was here, at an early stage of the development process, where the first steps were taken in imbuing the new BMW 3 Series Sedan with its impressive dynamic potential.