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SM Club de France
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The steering system in an automobile is the system that allows the driver to modify according to his will the trajectory of his vehicle according to the circumstances.
The vehicle stability, comfort and security will also depend on the steering system used on the car. The steering system is a main issue. Careful design has to be provided for this element. A perfect steering system has to fully comply with the following elements:
To comply with all these requirements and to allow the driver to use without any difficulty a car with a such exceptional road handling and a car with a high performance engine, Citroën created a new steering system which has no equivalent in the world.
The steering system goal is to enhance the security at high speed, and to speed up the movements at low speed and also to increase the comfort in removing any reaction. This breakthrough in the automotive domain at least equivalent to the hydropneumatic suspension breakthrough.
Since 1955, the DS was the first car to have the power steering as a standard equipment. At that time, a compromise had been found to have enough control for low speed handling without having a car with a too light steering wheel at high speed.
It took time for some drivers to get used to the smoothness of the direction at high speed, specifically on straight roads. We just have to remember how the steering systems were at that time to understand the necessity to need time to get used to the new Citroën steering system.
A same problem occurred for the power brakes of the DS Citroën demanded to have a quick action and to be very powerful to increase security, despite the necessity to the driver to learn to get used to a new range of effort.
In 1970, the SM shows a new standard in the automotive technology. This car delivers more power than the DS 21. Its top speed, required its ability to have a higher speed in cornering.
The top speed made mandatory the use of tires able to resist to the stress given by the ability of the car when cornering. High-speed stability imposes both very rigid tires to resist to the lateral drift and also a rigid as possible steering gear.
And the corollary is that for a same steering angle, the course change is stronger for a higher speed. We could conclude that we need to increase the steering ratio to obtain steering wheel angles as the one we obtain for a small course change, but the curves pushes us to see the problem from another point of view.
The SM, because of its power and road handling, can be driven at very high speed in curves; but the driver has to be able to turn the steering wheel in a very short time if he wants to have the benefit of the possibilities of the SM. For a same steering wheel revolution, the time to rotate the front wheels has to be shorter when the speed of the car is higher.
If we want a car able to corner rapidly, then the steering gear has to be direct and must use a source of power.
The direct steering gear advantages had been shown by numerous driving tests. A steering system using a low ratio gives a maximum of possibilities of handling on a sneaky road and whenever avoiding difficulties have to be done quickly, or whenever a course change has to be corrected (side wind, etc.).