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Roll cages are a significant part of any modern road car based racing car. They are required to provide the driver with a safety cell that will, in the event of an accident, protect him or her from injury. A down side of this is that it does add to the weight of the vehicle. Therefore, to try to make this additional weight beneficial all manufacturers use the roll cage to increase the torsional stiffness of the car as much as possible. To develop a cage to the most effective form can take a long time. For this process we use complex computer programs to perform "finite element analysis" to model the roll cage and determine how rigid the resulting structure will be before ever touching metal. |
2008 Vectra Roll Cage |
Rigidity is all important for creating a race car which is predictable and responsive to drive. The roll cage of a Touring Car is constructed from a collection of tubes that are welded together and welded into the basic road car shell forming an integral structure unlike the bolt-in variety popular in clubman racing. A modern roll cage will join and brace all major points on the car such as strut tops and suspension mounts. The best designs will try to keep the area of all apertures to a minimum. There are some areas where compromise has to be accepted, and one example of this is around the windscreen aperture where it is not possible to reduce the aperture size dramatically without impeding the drivers vision. By taking into account such factors when designing a cage the torsional rigidity of the shell can be increased approximately by a factor of ten.
Once the cage has been designed the shell shop will then produce the fully caged shell. A standard road car body shell is taken, stripped of paint and fittings where regulations permit. The latest British Touring Car regulations do not allow us to dismantle the road car shell other than removing the roof panel to aid fitting of the cage. To enforce this TOCA officials add seals to the bare shell which would break if dismantling took place. This bare shell is attached to a chassis jig which is extremely rigid and precise to ensure that the shell will not twist or distort whilst all the tubes of the roll cage are being added. Datum points are added onto the shell so parts can be accurately positioned and holes drilled as many of the roll cage tubes pass through bulkheads and the sills.
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A bare shell awaits roll cage insertion |
As well as the tubular structure of the cage all load bearing mounting bushes are added for suspension mounts, engine and subframe mountings, steering etc. The position of these points is critical so that operations loads from the suspension can be directed into the areas of the shell that are stiff and strong enough to cope.
