It's a very detailed chat, and a lengthy one too, but if you're really into your CSLs and M cars in general there are some fascinating revelations and geeky little facts contained. Go on, indulge yourself!
Click here to go back to the main article and abridged version.
When the decision was made to make a CSL variant of the E46 M3, what were the goals in terms of weight saving over that car? Did you have a specific percentage figure or was it just let’s make it as light as we can for so many euros?
HBS: “As light as we can. We can only make new components and parts that are going to be specifically designed for M. So the basic design requirements, the functional requirement that relates to the kind of parts that we want to do. We want to have a nice car, an optimal car for aerodynamics, and the function of the car needs to be perfectly designed for the M car.
“So it was all about reducing weight and making it lighter. We did have a figure in mind. We did have a target. We wanted it to go under eight minutes around the Nurburgring – that was the top target. So we had two options. You either increase performance, or you reduce weight. But you can also increase performance through the tyres.
“Now this is a mix of everything you see. We worked on the aero design, we worked on the chassis’ design, we designed a specific tyre combination and we also had the top performance of 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. And now they came onto the road in that car and they used to be in the pipeline.”
So it was almost like a running, working prototype for certain technologies you were experimenting with?
HBS: “Yes, yes, it was. Like the carbon fibre roof – there had been pre-development projects from BMW before. Not here in M, but elsewhere in the BMW group, and this way we were using the concept of realising carbon fibre. So we were able to use already existing development in the group to realise this roof – it was there already. The development was in the group, you know.
“So with that we were able to realise and produce this roof as the first series component. Do you know it’s a small component of what we call the BMW i philosophy today, and that was the best use of the car, of the roof, and we rolled it out to various coupes afterwards: E92 M3 and M6, for example. So we rolled it out more times.”
So, you didn’t purposely design the carbon fibre parts on the CSL and think these are just going to be for the CSL? It was always with a view to expanding and putting that sort of technology on other M cars?
HBS: “Of course, there has always been a desire to do that, so after the project started we proposed these components and the first series use had the highest costs – that was the CSL. Then after developing the processes then of course you get competitive edges when it comes to price, so you can manage to stop the technology costing so much.”
So that’s why it was £60,000 when it came out…
HBS: “But the roof of the M3 today is very similar to the CSL – only in processes, as it’s a new design – but we used the same processes. It’s a roof, sure, but making this in small numbers meant it would cost a lot of money. This was the first industrial application for a carbon fibre roof and saved around 7kg from the overall weight, lowering the centre of gravity, too. We also used lightweight materials for bulky items and we were able to use both components for subsequent models.”
If you look at the car next to a standard E46 M3, you can tell the lightweight parts in terms of the front bumper and the roof – they’re immediately obvious – but where else was the car optimised over a normal E46 M3 to save that weight?
HBS: “The rear window is a thin pane of glass – that was another optimisation.”
And the boot floor?
HBS: “Standard M3.”
Some people believe that the boot floor of the CSL is made of cardboard and can’t hold any weight, though?
HBS: “No, no. That was a joke actually, you know. Did they think it was real? We do have a paper composite used as the bottom in the boot, we do have that, but that’s the only cardboard I know of.
“You don’t see the chassis’ optimisations either. That’s not visible.”
In terms of trim, what sort of weight did you strip out of the interior over a standard E46 M3?
HBS: “110kg as a total weight reduction. That’s in total. Only interior – I don’t know exactly…”
HBS: “Yeah, around 50kg probably. We have 25kg in the seats, the door panels and centre console and back seats, so nearly 50kg.”
The wheels are much lighter than even the ones on the CS aren’t they? The CS had the same design but they weren’t quite as light?
PS: “Yes, its 2kg per wheel compared to the series production E46 M3 with 19-inch wheels.”
The chassis optimisations for weight obviously aren’t visible, but over a regular M3 of the time, where is the weight saved mechanically?
PS: “The lower control arms are in aluminium at the rear.”
And anything else that’s different to the normal M3?
PS: “Not for weight, but for position we used optimised the ball joints.”
And the geometry, is the geometry much more aggressive?
PS: “Yes, of course, so we increased camber and castor, too.”
Going back to the body and the trim, was carbon fibre always the material you were focusing on, or did you experiment with any other material to try and get that weight saving but maybe not at the same cost?
HBS: “Apart from the boot lid – that was an exception. That’s in sheet mould compound – the entire rear lid, inside and outside. It was more for aerodynamics. It wasn’t for the purposes of reducing weight only, it was rather for aerodynamics. Of course you don’t want to shift the balance of weight between the front and rear axle – that was one reason.”
So what’s the weight distribution? Is it 52:48, front to rear?
PS: “No, it’s 51:49. The standard M3 was 52:48. There’s no extra weight at the rear in the CSL, it’s just changing the distribution by reducing the weight at the front.”
HBS: “We can also talk about the bumper. From a series production developer like myself actually the front bumper is a racing car component. It’s a carbon fibre shell made in the autoclave. It doesn’t have the plastic or aluminium carrier structure of the standard M3’s bumper – it’s different. So we accepted the risks specifically for this car in terms of cost.”
How much, then? 4,000 euros?
HBS: [Laughs] “Yes… I asked my boss if he wanted to have it light or inexpensive. He said light…”
And the exhaust system – was that lighter than the standard car? Thinner walled?
PS: “I don’t know. I think so… The air intake is light, because it’s carbon.”
HBS: “I’m not sure…”
What about spring rates and dampers settings?
PS: “Yeah, this is also special, optimised for the CSL. Every part. I don’t have the right figures, but it’s higher spring rates and optimised damper settings.”
Presumably a stiffer anti-roll bar as well?
Coming from the E36, there was the E36 M3, then the GT. You move to the E46 and the E46 CSL – why didn’t you think about a CSL for the E36, or even the E30? What was it about 2003 and this car that made you think it was the right time to produce a CSL? There hadn’t been one out for 30 years or so, so why was the time right?
HBS: “The previous model – the E36 M3 – was watched very closely internally by BMW. Every one looked at its sportiness. And it was the danger that the M3 became too sporty. With the E36 M3 we showed a rear wing as well, and it was decided not to go with it because it was the idea to be a bit more withdrawn politically. That was quite difficult back then. There was a challenge that M cars should function on the road very perfectly and also on the race track. So you have to decide.
“We were very careful with the E36 in that you could get an M3 and an M3 with a sports package. If you compare these two, there’s not much of a difference. We knew that the M3 customers would be sad, but that’s why we were so inspired with the E46 CSL. We could do things like make the wheel arches wider and the chassis more differentiated form the standard car, and then the carbon fibre parts were just another add on.”
Moving to where BMW is now, we’ve got the M4 coming soon, and also with the carbon fibre technology and the partnerships you’re entering into with the BMW i sub brand, do you think there could be crossovers with the lessons you’ll learn from carbon fibre production with the i cars fed back to M cars – especially given the fact that you’ve gone turbocharged to help lower emissions and trying to lower weight by using these lightweight materials?
HBS: “Definitely, absolutely. Not at once, not right away. Our bodies are made in sheet metal, whereas BMW i cars are made specifically in a factory designed for carbon fibre construction. And still they’re faced with a challenge.
“We called it ‘intelligent lightweight’ with the CSL and its carbon fibre parts, so we don’t have to re-invent the planet completely. Because we build our M Cars – M5 and M6 in Dingolfing and the M3 here in Munich – as assembly line cars, we would need to look what is available. So if we reinvent it completely, it will not be affordable.”
That’s true, but if you look at McLaren with its carbon fibre tub on the 12C, is there room in the BMW range in the future for an out-and-out carbon fibre chassis hypercar above the i8 – as that’s really to showcase the i sub brand?
HBS: “I’m not a member of the board unfortunately…”
But you’re not ruling it out…
HBS: “I’d love it. It’d be an engineer’s dream. I’d be the first one to raise my hand if they asked us to do it. But one other thing, you know a supercar, that’d be a completely new process.”
Surely the lessons you learn with carbon fibre as part of the i projects can be transferred to other areas?
HBS: “Yeah, absolutely, of course. So the roof of the CSL to project i, it can also be done vice-versa.”
So between chassis and body and trim, what are your favourite parts of the car? When you signed the car off, what were you most proud of, the best thing you’d achieved with the E46 CSL?
HBS: “I can’t pick one thing. You have to look at the whole thing, the entire piece of art. It all works together. I was allowed to drive it once on the Nurburgring and I will never forget it. That will stay with me forever. It’s the whole thing.”
PS: “At that time I think it was because the task for this car was to be faster than eight minutes on the Nordschleife, so the question was what is necessary to achieve that goal?”
HBS: “I think it’s one of the most emotional M cars of the past.”
If you can’t tell me what your one favourite part is between you, what’s the one thing you would do differently if you had the opportunity again. You’re an engineer, so there must be something you’d do differently…
HBS: [Laughs] “Well, we search for improvements in lightweight materials – that’s an on-going process, right. And we have a lightweight carrier for the instrument panel we developed for the car, and it’s been published in material papers. It was originally designed for current M3, but it didn’t work, because it was not mature enough for series production. Just as an example, there are other components that had potential, but there were no series production processes at the time which fell into the budget to make production and the car’s end price affordable. There is potential, but it has to be affordable for the customer at the end of the day.”
Why was there no manual option on the car? Why offer it with just the SMG gearbox?
PS: “Race car technology. So it’s paddleshift.”
It’s interesting to look at how far paddleshift gearboxes have come in 10 years – DCT on M3, M5 and M6. I don’t mind this gearbox as you get quite a lot involvement with it. You feel it and hear it as you change gear, but wasn’t there a case for a manual?
HBS: “Using two gearboxes means there would have been more effort involved if you had two versions.”
Did you think about adaptive dampers at the time, or did you consciously want to go for a fixed rate damper?
PS: “Yes, we didn’t think about adaptive. We wanted to keep it plain, less weight, as simple as possible.”
So you were prepared to have a few more compromises on the road to achieve that ultimate performance on the track?
PS: “Yes. As in a race car, we lowered the variety of situations it had to work in. It was a special task, it had to lap the Nurbrgring in under eight minutes and that was it.”
Does it ride any lower than a standard M3?
PS: “Yes – at the front, it’s 10mm lower than a standard M3. Only at the front.”
Did you think about under body aerodynamics in the development of the car at all?
HBS: “Yes, there’s a cladding under the front to smooth airflow, but that’s as far as we went.”
And how much ram air effect do you think you get – how much extra horsepower do you think the scoop into the airbox gives at speed?
PS: “I think it’s around 10hp in total as you have high pressure in the airbox like a sports bike. In this car you don’t even measure the air intake, you calculate the air coming in. So it was already to high resistance with too much air for the measurement unit, so they took the measurement unit out like an air restrictor.”
So you measure air pressure?
PS: “Yeah, air temperature and pressure. That’s how we calculate it. That’s why we needed a more powerful control unit, because they have to calculate more as this car has higher potential. So really big steps for the last few hp.”
If you deleted air conditioning and the stereo, how much extra weight would that save you?
HBS: “21kg for air conditioning, and for the radio, I’m not sure. It was a no cost option. But you don’t need the air conditioning in England, no…?”
No, we do – it helps stop the windows steaming up in the rain. And the strut brace, how much of an effect does that have?
PS: “It gives you much sharper turn-in, much more precision at the front over the normal car.”
You wanted to target eight minutes for the Nurburgring and you wanted extra performance, so you changed springs, dampers, lighter wheels, more power, lighter interior. Why did you not put more emphasis on changing the brake setup?
PS: “Well, there’s a bigger disc in the front – 345mm for the CSL and the normal car has a 325mm disc. And the tyres were only for the CSL. We had a similar tyre for the current M3, but not quite a extreme. For the CSL these were very extreme.”
What sort of lateral g can you pull on those?
PS: “I think 1.4 lateral g, measured by Sport Auto. The rear brakes are the same, like the standard series M3.”
The guys who track there cars regularly, a lot of them put AP Racing calipers and discs on the front, as the brakes are thought to be the weakest point and fade quite a bit.
PS: “This was a series production car though and we still needed that compromise, as although we wanted race track performance, we still needed it to be a road car. We have special pads available with a different compound if you want to choose them.”
So you didn’t consider Perspex or anything even lighter for the windows? You wanted to keep glass for refinement?
HBS: “Yes. We dared to do that only with the GTS.”
So why not call the GTS a CSL. What was the reasoning behind that?
HBS: “That’s a different concept anyway, the GTS. There were less cars – the quantity was less. It’s more extreme. There’s no rear bench, there are four-point belts, there’s a roll cage and we have certified seats registered for racing. That was the problem – the complaint that they had with the CSL. They said there were no six-point belts available, so we gave it to them with the GTS. It’s rather a collector’s car, a racer’s car, the GTS.
“The GTS is only 125 units. The CSL, we honestly didn’t know how many cars we were going to produce. We discussed that, but we didn’t want to set a limit. We ended up having 15 to 16 hundred.”
Do you know what the final production total was?
HBS: “In the museum we say 1,383 – that’s the official number. And a few more tucked away somewhere…”
There’s a big CSL following in the UK – I don’t know if the same thing happens in Germany, but they say the black ones are faster…
HBS: “The CSL drivers were here this morning from Great Britain but 95 per cent of them were silver grey…”
Yeah, in the UK the black ones are much rarer.
HBS: “Yeah, the UK was the single biggest market in the world for the CSL. 422 cars were sold to the UK. That’s very British…
“At the beginning we thought we would make the car more extreme as well. We discussed scrapping the rear bench seat completely to make it a two-seater car only and save more weight. We discussed that and the answer was we couldn’t. That would have saved us the job of having to develop the folding mechanism for the front one-piece bucket seat, but sales insisted on having a four-seater. They had to develop the carbon fibre centre console and the concept car of 2001 also had the rear seats. We discussed it with the GTS but for the CSL there was still some need for day-to-day usability, so it was an issue. It was all discussed though.”
The concept car had a carbon fibre cam cover, too, how come the road car didn’t get that? Was it because of cost?
HBS: “Yes, I think because of cost. Because the interior trims were also designed in carbon fibre as well, originally. The dashboard in the concept was originally meant to be carbon, but we decided to go with regular materials for the interior of the series production car. But we did realise a lot of carbon fibre features from the concept car.”
Are the radio and the speakers more basic than in the normal M3?
PS: “No… they’re basic items from the normal car.”
It sounds very tinny…
PS, HBS: [Laughing]
When you’ve got that noise to listen to though, I guess it doesn’t matter.
PS: “Yeah, that’s the sound generator!”
HBS: “So it’s no problem without air conditioning or the radio – you know, you have your windows down to get the ventilation and you listen to the engine…”