A SHORT HISTORY OF SUSPENSION  

The same is true of a car's springs. They have to be designed on the basis of the weight to be carried. This, of course, is troublesome, as a car is always having to carry different loads (from its weight unladen to the maximum load). On the one hand, it is desirable for the springs to be as soft as possible. On the other, they must be able to carry the load and cope with load variations.
 

Serpollet three-wheeler.  1891
 

Polaire, the actress, with her car.  1905

This causes a dilemma: either we choose a spring which is very hard but not very sensitive to load variations, in which case the suspension lacks elasticity and will not fulfill its purpose; or else we choose a soft spring, but then any load variation will significantly change the behaviour of the suspension.

The solution would be to adopt a suspension with its flexibility varying on the basis of the load. The greater the weight to be carried the harder the spring would become. In this way, the correct behaviour of the suspension would be maintained. The flexibility of the spring would automatically be adapted to load variations.

This solution exists. It is termed variable flexibility suspension, i.e., its flexibility decreases as the load increases.

It will be seen below how and why air -- air again! -- is in practice the most suitable medium for this type of suspension. First, we must study some other inherent suspension problems.
 

Serpollet cars in the Bois de Boulogne.  1898