The Laws of Physics

There are two fascinating sides to the world of physics not everybody may realise right away: First, physics provide a clearly defined foundation for all driving processes in a car; second, nobody can go beyond the laws of physics, which are the same at all times and in all places.

Setting out to develop a new and truly thrilling sports car, the M3 CSL, the engineers at BMW M focused from the start precisely on these straightforward laws and principles. Reminiscent of a long tradition at BMW, the abbreviation "CSL" stands for Coupé, Sport and Lightweight. The legendary 328 Mille Miglia Coupé, for example, dates back all the way to the year 1938 and features an all-aluminium skin. Then, in the '70s, a lightweight sports car was built in small numbers on the basis of BMW's 3.0-litre coupé.

After taking up this theme once again at the Frankfurt Motor Show in 2001 with the first M3 CSL Concept Car and receiving overwhelming feedback from customers and the public at large, BMW subsequently decided to build the M3 CSL as a production car. Whilst not quite as elaborate for reasons of cost as the extremely light Concept Car shown in Frankfurt, the road model naturally lives up in full to the myth of the CSL with supreme performance, thrilling agility and outstanding driving precision all combined in one.

The definition of dynamics goes back 300 years

What is so special about the letter L in the abbreviation CSL and what does it mean in terms of physics? The answer is clear and convincing: Back in the 17th century, Sir Isaac Newton, the English physicist and astronomer, discovered and expressed the basic equation of dynamics: F = m x a. In simple terms, this means that force F is the product of mass m times acceleration a. Now, looking at this formula from the perspective of a, meaning that a = F/m, we see that acceleration - a - increases or becomes faster with every increase in force F and every reduction of mass m.

Both simple and easy to understand, this means in the case of a car that every kilo of superfluous weight deprives the car of its power and performance in accelerating. So the engineers building highly dynamic cars such as the BMW M models are able to follow two possible approaches in practice: They either improve acceleration by increasing F, the force or power that drives the car, or - and this is far more difficult - they reduce mass m.

It is fair to say that even the "standard" M3 does not have any lack of power, the car's high-speed engine concept derived from Formula 1 providing maximum output of 343 bhp (252 kW) at 7,900 rpm.

The far more interesting and challenging option is to optimise mass m, since, with customers expressing increasing demands in terms of motoring comfort and with cars therefore being equipped to an ever-increasing standard, even thoroughbred sports cars have in the meantime "put on a bit of fat". So now the engineers and other specialists creating the M3 CSL seek to make a clear departure from this upward weight spiral and introduce a new philosophy.

More power alone is not the solution to better dynamics

Whilst an increase in the power or force factor F, that is the philosophy most manufacturers follow in the market, serves primarily to improve a car's longitudinal dynamics, that is its straight-ahead acceleration, a decrease in mass m offers advantages in both longitudinal and lateral acceleration. A simple comparison: Increasing only the power of a car versus the regular or standard model, we are able to improve the car's straight-ahead or longitudinal dynamics, meaning that the car will now accelerate faster in a straight line and may also achieve a higher top speed.

Reducing the overall weight of a car, on the other hand, and possibly increasing engine output in the same process, we are able to significantly improve the car's lateral dynamics as well as its positive and negative longitudinal dynamics. On the road, this means that the car not only accelerates faster, but is also able to achieve a far higher speed in bends and come to a standstill more quickly when the driver applies the brakes. Precisely this is the approach taken by the engineers at BMW M with the new M3 CSL, creating the foundation for a truly unique, purist driving experience.

Nurburgring and motorsport - two of the M3 CSL's most significant genes

The Northern Circuit of Nurburgring, probably the most demanding and challenging race track in the world, plays a very special role in achieving such a high standard of driving dynamics. After all, this 20.8-kilometre circuit through the Eifel Mountains has always been a significant test track in developing and consistently enhancing the driving dynamics of every M Car. This is where, in the "home" of the M3 CSL, all criteria in driving dynamics are put to the test. This is where the supreme stand out clearly from the mediocre and even the good, since the interplay of all car components can be measured in terms of simple and straightforward lap times.

This is also where a genuine sports car is able to demonstrate its purist standard of driving dynamics, its thoroughbred character as a genuine driving machine. What makes the difference is the way a car "feels", the feedback it gives the driver from the chassis, suspension and steering.

This dynamic driving experience reaches its supreme standard in motorsport where absolutely no compromises are required, say, in terms of comfort, where weight is consistently reduced in the interest of dynamic performance.
Weight reduction is therefore the name of the game - and there are several ways to reduce the weight or mass of a car. The first option is simply to leave out a number of parts and components - a purist, but rather limited approach. The second option is to use especially light and/or high-quality materials instead of conventional parts made of conventional materials in a conventional car. But relying on one single lightweight material would not have been a genuine BMW M solution, which is precisely why the M3 CSL follows a philosophy rightly referred to as "intelligent" lightweight technology.
Intelligent lightweight technology is the answer.

Intelligent lightweight technology BMW M-style means using the right material in the car at the right point. In other words, the most suitable material is used for each part and component of the car, since every material has specific features and properties to be taken into account. In particular, these are physical properties such as heat resistance, elasticity, flexural strength or stiffness. But criteria such as quality and ease of production must of course also be considered.

First and foremost, the M3 CSL uses materials such as carbon-fibre-reinforced plastic (CFP), glass-fibre plastics carried over from aerospace, aluminium and other lightweight materials wherever they are most appropriate. For comparison, steel, still the material used most often in automobile production, has a density of approximately 7.8 kilos per cubic decimetre, whilst aluminium (2.8 kilos per cubic decimetre) or carbon-fibre-reinforced plastic (1.8 kilos per cubic decimetre) have a much lower level of density.

Benefitting from this consistent reduction of weight, the M3 CSL weighs just 1,385 kg (3,054 lb), equal to a power-to-weight ratio of 3.85 kg/bhp. This improvement by approximately ten per cent over the "standard" M3 lifts the M3 CSL into a new dimension of dynamic performance.

The M3 CSL simply exudes agility and driving dynamics at very first sight. Even from the front, when viewed for the first time, the CSL stands out clearly from its more "civilian" M3 counterpart through its completely different carbon-fibre-reinforced plastic front air dam serving also as a support element and featuring a very dominant intake air opening for the engine on the driver's side (measuring 9 cm or 0.35´´ in diameter) as well as two individually exchangeable flaps visibly finished in CFP. These flaps alone reduce lift forces at the front versus the standard M3 by more than 50 per cent.

Innovative materials at exactly the right points

With the new rear diffuser made of CFP clearly visible at first sight, the new rear lid of the M3 CSL with its integrated spoiler made of SMC (sheet moulding compound) is equally outstanding. The engine compartment lid, in turn, is made of aluminium, as on the M3. The front bumper support - like the front air dam - is made of carbon-fibre-reinforced plastic and therefore also serves an important weight-reducing function even if it is hidden away out of sight. The rear bumper support, on the other hand, is made of endless- glass-fibre-reinforced plastic, to be specific a glass-fibre thermoplastic material carried over from aerospace applications.

The roof made of carbon-fibre-reinforced plastic again visible at first sight is particularly conspicuous, representing one of the most attractive signs of distinction on the new M3 CSL which will catch your eye at first sight. Indeed, this is where intelligent lightweight technology serves to raise driving dynamics to a very high standard, the carbon-fibre roof not only being six kilos lighter than the conventional steel roof of the M3, but also helping to significantly lower the car's centre of gravity thanks to this reduction of weight where it really counts.

The roof of the M3 CSL is built at BMW's Landshut Plant

BMW builds this carbon-fibre-reinforced roof itself at the Landshut Plant, where, at the home of BMW's lightweight technology experts, specialists acting as highly competent system suppliers make the roof of the M3 CSL out of several layers of this expensive material. The in-house suppliers at the Landshut Innovation and Technology Centre (LITZ) therefore not only contribute their particular skill and competence in this way, but also ensure fast and flexible action in implementing the most sophisticated innovations in lightweight technology.

Even parts and components normally quite insignificant within the body structure as a whole were carefully considered for any possible reduction of weight. Focusing on the floor of the luggage compartment, for example, the engineers at BMW M opted for a paper-honeycomb-sandwich structure. The through-loading facility, in turn, made of steel on the "standard" M3, is made of a sandwich endless-glass-fibre mixture of thermoplastics and foam on the M3 CSL. And the rear window is made of extra-thin glass.

The body shell of the M3 CSL is still made of steel panels varying in strength and thickness quite simply because in some cases it hardly makes sense to replace steel by another material. Here, therefore, steel continues to prove its qualities and advantages also in terms of stability.

A top performer with outstanding agility

It goes without saying that a car as thrilling as the new M3 CSL requires the right kind of chassis and suspension. After all, the driver should really feel the agility of this car, agility should be an important part of the CSL driving experience. So in developing this dynamic suspension and chassis system, the engineers at BMW M again focused on motorsport, which is no surprise considering the very long list of racing wins and achievements by BMW touring cars in more than four decades.

The most important parameters in this context are of course the wheel suspension as such, the steering and brakes - and the tyres also play a very important role in providing a supreme standard of driving dynamics on the road.
The significant but very tempting challenge the engineers at BMW M were happy to accept was to leave the outstanding chassis and suspension of the M3 unchanged in its basic philosophy, but to thoroughly refine many features and the general set-up in view of the change in weight. In this process of optimisation starting at a very high level, each individual component was put to he test in every respect, being carefully examined for every possible improvement. Now the result is a chassis, which from the very beginning simply feels different from the "regular" chassis in the BMW M3, offering an even higher standard of precision and agility on the road.

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