Car springs work under high variable loads. Therefore, in order to increase the fatigue strength, a special treatment called peeling is used. It is about this, that the feathers are subjected to the cold impact of a stream of cast iron or steel pellets rushing at high speed. Rolling of the spring leaves significantly increases their durability. Depending on the position of the springs in relation to the car frame, they are divided into longitudinal, seated along the car and on the transverse, attached across the car. Due to the mode of operation, springs are distinguished: semi-elliptical quarter-elliptical, cantilever and double. Double spring, used in trucks, consists of two springs: main and secondary. When the car is unladen, then the main spring works; the additional spring is only activated when the vehicle is properly loaded.