Designing a BMW 3 Series is one of the hardest tasks in the motor industry.

12.5 million have been sold to date and it is the world’s best selling premium-make car. It is also the best selling BMW and thus, says BMW Group design director Adrian van Hooydonk, the BMW people see on the road more than any other.

‘It has to look like a BMW, it has to say BMW to people. And any new design themes we want to introduce have to be seen on this model.’

This is why the F30 BMW 3 Series is no great break from tradition. To do anything other than evolve the classic long-wheelbase, short front overhang proportions would be wrong. That’s not to say the new one simply repackages the looks of the old, though. To explain what makes the new 3 Series special, Hooydonk talked through the new car…

Front

The precursor to a 3 Series, the 1968 BMW 2002, had single headlights and tall kidney grilles. This was where the facial graphic of the 3 Series was born. Come the 1983 E30 3 Series, twin headlights were fitted, cut off by the bonnet at the top to concentrate the look. The new 3 Series carries this theme on yet further.

The double headlamp look is retained, this time with the cylinders picked out by vivid white daytime LEDs. The bonnet cutoff is this time depicted by a ‘razor’ bar on top of the light. The grille is also wider and attached to the grille for the first time, a styling trick that makes the whole front look lower and wider. Debuting here, the look is coming to other BMWs too.

Side

This must express dynamic movement. ‘Design is a promise’ says Hooydonk. Two feature lines do this, moving upwards toward the rear to suggest forward motion. ‘The 3 Series is the sprinter of the family, and the design hints at a quick getaway.’

Hooydonk compares the angle of this feature line to that of bigger BMWs. On the 7 Series it is horizontal, running the entire length of the car unbroken. ‘This expresses presence and luxury.’ On the 5 Series, it is more angled, to help give it a strong autobahn-ready look. ‘The 5 Series has to express speed.’

Rear

The rear is the most familiar aspect to current 3 Series owners. Here, BMW has looked to enhance the car’s solidity by visual tricks that make the rear look wider even than its additional dimensions portray. Hooydonk’s goal was to make it look more cohesive than the current car, courtesy of subtle improvements to the shape of the now more vertical bootlid and better-configured bumper shape.

Details like the new L-shaped lights are a typical BMW trademark: here, they have a more diagonal upper edge to suggest sportiness ‘and there are two light bars within them at night: the 5 and 7 have three’.

Interior

‘The interior of a 3 Series has to develop round the driver, and we have enhanced this cockpit feel with the new car.’ Hooydonk says it has a strong asymmetry in its design, that extends from the upper dashboard itself right through the centre console and between the front seats. ‘It is more asymmetrical than any other BMW car.’

Premium details feature heavily. It has the black panel instruments of the 5 Series, plus a super-wide iDrive screen taken straight from the 7 Series. ‘It is the first time in this class a car has had such a large screen.’ The standalone design mimics modern flatscreen TVs, while a further nod to technology comes in additional stowage space inside. Smartphones, digital cameras, music players: ‘We all have many things we want to dump in our cars’.

Summary

Designing a BMW 3 Series is a heady task. It is such an icon, the stylists simply can’t get it wrong. While the F30 is familiar, it’s also more modern and stand-out in the key area that has long defined the 3 Series, the front end. Like it or loathe it, you’d better get used to it, as you’ll be seeing a lot of them on the road once the car is launched on 11 February 2012.

But do you like or loathe it? Do you agree with Hooydonk’s interpretation of what a 3 Series should be and how it should look? Share your thoughts on the look of the new F30 BMW 3 Series…

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LEARNING how to do folding hard-top roofs with the 3 Series Convertible served BMW well.

It meant it could launch a folding hard top Z4 relatively easily – simply because it had acquired so much knowledge.

What’s more, the shift over to the folding tin top is another reason for the car’s production relocation to Germany.

The Regensburg plant where it’s built has now become BMW’s official ‘centre of excellence’ for folding hard-top roofs.

It’s so well geared up, the supplier is even located there on site, an engineer insider told me.

‘This gives us the best possible means of achieving high quality levels.’

Engineering a folding hard top isn’t the work of a moment. Even one such as the Z4’s, whose lower 2-panel count reduces the number of joins and joints to worry about.

The problem come in areas you probably don’t even think about. Such as?

•    Packing the roof into the boot without the lardy bum of a Peugeot 307 CC. ‘A close working relationship with the designers is vital.’

•    Making it watertight – ‘this is the key. The biggest challenge is not to get the roof moving, it’s to keep the water out.’

•    The need to like coffee. ‘I was able to work closely with the expert from the 3 Series Convertible project – we could have coffee, chat about our weekends, and how to get the Z4 roof watertight. We did this a lot…’

‘Once you’ve got it watertight the first time, you then need to do it again. Repeatability is of huge importance.

‘Our approach is to always take one car at random and test it for water tightness.’

Passing the tough BMW test involves putting the car in a high-pressure shower. Literally. ‘It’s a severe test. At the moment, every car is being tested. In time, tolerances will be such that we can test a certain percentage.’

What’s a watertight test pass rate for BMW? 95 percent ‘right first time’. Which means that, basically, every single Z4 has to be built to be watertight.

‘We’re almost there…’

BMW Z4 development background

BMW Z4 chassis secrets

BMW Z4 photo stream on Flickr