CSL development team: PH Meets

PH talks carbon roofs, cardboard floors and more with the engineers who built the M3 CSL

Carbon fibre on road cars is commonplace now, but even 10 years ago it was an expensive, rarefied material reserved only for the top echelons of motorsport and ridiculous million pound hypercars. The E46 M3 CSL changed that.

Carbon's everywhere now but the CSL was a pioneer

Far from being a bolt-on special, BMW’s M Division engineers employed a considered analysis of using composite materials to turn the regular E46 M3 into the CSL, warranting the addition of that iconic boot badge. But what exactly was the motive behind the decision to make an M3 CSL back in 2003?

According to Hans-Bruno Starke – the engineer behind the CSL’s lightweight body and trim parts – “the time was right. The E36 M3 was watched very closely internally by BMW. Everyone looked at its sportiness and it was the danger that the car would become too sporty. The idea was to be more withdrawn politically, and we knew M3 owners would be sad at that. But things changed and that’s why we were so inspired when it came to the E46 CSL, we were allowed to differentiate it more from the standard car – make the wheel arches wider, the chassis more extreme and use carbon fibre parts.”

With the development team given the green light to make the M3 more hardcore, were there certain parameters the CSL had to hit? Yes, and Starke outlines the development goals thus.

BMW wanted the M3 less extreme ... oops!

“We just said ‘let’s make it as light as we can’. We wanted to have an optimal car in terms of aerodynamics and performance, but it still had to be functional on the road. We did have one target though – we wanted it to go round the Nurburgring in under eight minutes, so we had some options. You can either increase the performance, or you can reduce weight. But you can also increase the performance through the tyres, too.

“The CSL is a mix of everything. We worked on the aero and chassis design and designed a specific tyre combination. We also employed lightweight design – that’s what we realised with this car. We were able to design parts that had only been in the pipeline in BMW as pre-development items. They made the jump onto the road from the experimental stage.”

So the CSL was effectively a running, working prototype for future BMWs then?

Carbon on the body, and under it too

Starke elaborates. “Yes, yes it was. Like the carbon fibre roof – there had been pre-development project from BMW before elsewhere in the group, and we utilised this existing development for the roof. With that we were able to realise the roof as the first series carbon component and roll it out onto later M cars. It’s a small part of what we call the BMW i philosophy today.”

Composite materials aren’t cheap now, let alone over a decade ago when the car was in development. BMW knew this, hence dipping its toe in the carbon fibre pool with the CSL before making the materials available on more standard M cars.

“There was always a desire to use it [carbon fibre] on other cars. After the project started we proposed these components and the first use had the highest costs – that was the CSL. But once you develop and refine the processes, you find competitive edges when it comes to price, so you can manage to stop the technology costing so much.”

You'll not be wanting to replace that bumper...

So that’s why the CSL cost around £60,000 when it came out… But it truly was an innovative car in terms of its construction. No production vehicle built in similar numbers before it (officially 1,383 were made, with “a few more tucked away”, according to Starke) used the material as widely.

“The roof was the first industrial application of carbon fibre and saved around 7kg, lowering the centre of gravity, too. The front bumper is actually a racing car component. It’s a carbon fibre shell that doesn’t use the plastic or aluminium carrier structure of the standard M3. It costs around 4,000 euros.

“The rear window is a thinner pane of glass, but we kept that material to retain refinement. The total weight saving was 110kg [dropping the kerb weight to 1,385kg] and we must have taken around 50kg out of the interior – the door panels and centre console are carbon and the seats save around 25kg.” Looking at the original press pictures of the CSL [pictured] we can see just how lightweight it is.

Lighter wheels and stickier tyres part of the package

“Actually, we discussed scrapping the rear bench seat completely to make it a two-seater and save more weight, but sales insisted on having a four-seater,” adds Starke.

And the infamous ‘cardboard’ boot floor?

“That was a joke. Did they think it was real? We do have a paper composite used at the bottom of the boot, but that’s the only cardboard I know of…”

The lightweight body and trim parts complimented the chassis. According to Peter Schmidt – the man behind the CSL’s chassis – the wheels are 2kg lighter than the 19-inch E46 M3 wheels, while the lower suspension control arms at the rear are in aluminium.

Without provocation Starke earlier touched on something with modern day relevance – the tie in with BMW’s i sub-brand and its carbon fibre constructed cars. The modern quest for ever more efficient vehicles is being achieved by downsized, forced induction motors and lightweight materials, so will lessons learnt from the CSL onwards and technology and processes from the i cars be utilised in future M products?

Evocative badge, still held dear by M engineers

“Definitely. Absolutely. With the CSL we called the philosophy ‘intelligent lightweight’ [the same as BMW calls it today] so we don’t need to reinvent the planet completely. Just like the CSL’s roof, the process can be done vice-versa.” There’s great potential, then, that lightweight instrument carriers and carbon fibre panels could feature on a special version of the M4.

With the CSL, the lightweight engineering worked, and the M Division boffins achieved their goal. The car lapped the ’ring in 7min50sec. “It’s one of the most emotional M cars of the past,” believes Starke.

For the full transcript of Sean's chat with Hans-Bruno Starke click here.

BMW's released a short video about the 10th anniversary trip to Munich that PH joined - see here.

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