Chassis - Body Structure
After 45 years, Alfa Romeo has resumed and "democratized" the 33 Stradale concept, creating the 4C. The great technological development and the newly developed design techniques of the last 20 years have allowed the use of materials which were previously used only for military and aerospace applications.
Composite materials in particular have evolved very quickly and their characteristics have made them attractive for sectors which are sensitive to performance, such as car racing, that require very limited production volumes and are not so subject to cost restrictions.
Applications of composite materials for manufacturing vehicle chassis have so far been limited to supercars costing at least 200, 000 euros, or vehicles with very limited usage possibilities on roads open to traffic.
The 4C makes extensive use of composite materials, and is offering for the first time a true sports car with carbon fiber body at the price of a prestigious saloon.
The technicians had to face many challenges:
- High cost of materials
- Difficulty mass production application
- High design complexity
All this contributes to obtaining two main advantages: a high level of integration between components (a single complex carbon part instead of many welded or bolted steel parts) and a considerable reduction of weight.
To understand the advantages provided by the use of carbon it is useful to compare this material with "conventional" alloys and metals, called "isotropic" since they have the same strength characteristics in all directions. Carbon fiber, on the other hand, is processed to guarantee a one-way direction of the fibres, and improve the material's robustness in one specific direction. The direction of the fibres in each part of the component (in this case the chassis) is decided during the design stage, in order to maximize the resistance to the stress experienced by the car during use. The following diagrams highlight the differences compared to isotropic materials: taking steel as a reference, the density (i.e. the weight of a specific volume of the material) of carbon fiber is seven times lower, while resistance is five times higher.
The 4C is not only the first sports car of its category to offer a carbon fiber chassis, it also improves production of a wide range of components, adopting innovative production methods that are difficult to apply to mass production, where the conventional use of pressed steel predominates.
As can be seen in the images above (and below), the 4C chassis is dominated by the central carbon fiber "tub", which houses the passenger compartment and includes the attachment points of the front suspension
In the various carbon layers there are brackets with threaded holes (in the front and rear part), on which the front and rear aluminium frames are installed.
A sturdy high resistance steel roll-bar is positioned behind the passengers. This prevents passenger compartment deformation in the event of roll over. The roll-bar is also screwed onto the carbon chassis, thanks to two steel brackets with threaded holes inside the carbon layers. The aluminium structure protects against frontal impacts, while the second aluminium structure creates a "cradle" on the back, to which the mechanical part of the car (engine and transmission) is attached, and includes the attachments of the rear suspension and a further lower structure with controlled deformation, which protects against rear impacts. Both the front and rear aluminium structures and the aluminium tub feature significant differences on the versions to be sold on the US market, in order to comply with the various regulations in force for crash tests in that country.
The differences in the European and US versions of the front chassis are indicated below. (front view)
There are differences between the European and US versions of the aluminium front chassis. The various colors indicate the different characteristics of the US and European chassis.
- Parts in red: specific parts added
- Parts in blue: parts in common but different thickness
- Parts in yellow: same volume but different thickness
- Parts in grey: parts in common
The following, on the other hand, are the differences relating to the European and US versions of the rear chassis.