Rubber springs

From a mechanical point of view, rubber springs are distinguished from other springs by their low modulus of elasticity and the variation of this modulus of elasticity with the shape of the spring. As the modulus of elasticity is low, the shape varies significantly with load, resulting in a variation in modulus and therefore flexibility with spring load. This effect is particularly noticeable with compression springs.

In addition, rubber springs are highly resistant to dynamic stress and have a high self-damping capacity, which means that part of the energy supplied is converted into heat inside the spring. As springs are poor conductors of heat, internal heating can be significant. It should also be noted that the modulus of elasticity varies with temperature and with the speed of load application.

Given all these interacting factors, it's understandable that it's not possible to obtain properties from a rubber spring as precise as those you'd expect from a metal spring; on the other hand, it's fairly easy to obtain the desired modulus of elasticity through the choice of elastomer or mixture proportions (article General considerations in this section Springs), as these parameters vary the modulus of elasticity considerably. In practice, we estimate their influence by measuring the Shore A hardness of vulcanized rubber.