Car spring modification

The coil spring is the most commonly used spring of the suspension system because it is easy to manufacture, high performance and efficiency, and low price. The definition of a spring in physics is to store energy. When we apply a fixed force to the spring, it will deform. When we remove the force, the spring will have a tendency to return to its original state, but the spring will shake when it rebounds. The amplitude tends to exceed its original length, and it will not slow down the free shock caused by the spring rebound until there is frictional resistance, which is usually the task of the shock absorber.

The general spring is the so-called “linear spring”, that is, when the spring is stressed, its compression deformation follows the “Hooke’s law” in physics: F=KX, where F is the applied force, K is the elastic force coefficient, and X Is the amount of deformation. For example, when a linear spring is subjected to a force of 40Kg, it will cause a compression of 1cm, and then every increase of 40Kg of applied force by 1cm will definitely increase the amount of compression. In fact, there are other pressures on the suspended springs. Even when the springs are fully extended, the springs are still under pressure to fix the springs on the car.

In the traditional spring and shock-absorbing cylinder suspension design, the spring acts to support the body and absorb the impact of uneven roads and other forces on the tires. The so-called other forces here include acceleration, deceleration, braking, turning, etc. The force caused by the spring. What’s more important is to keep the tires in constant contact with the road during the vibration elimination process to maintain the tracking of the car. Improving the contact between the tire and the road is our primary consideration for improving handling.

The main function of the spring is to maintain the comfort of the car and keep the tires in full contact with the ground. Using the wrong spring will have a negative impact on the driving quality and handling. Imagine if the spring is completely rigid, the suspension system will not work. When the car jumps up on uneven roads, the tires will completely leave the ground.

If this happens when accelerating, braking or turning, the car will lose track. If the spring is very soft, it is easy to “sit on the bottom”, which means that the suspension travel will be exhausted. If sitting on the bottom occurs when cornering, it can be considered that the spring coefficient becomes infinite (there is no compressed space), and the body will have an immediate weight transfer, resulting in loss of tracking.

If this car has a long suspension stroke, it may be possible to avoid the “sit bottom” situation, but the relative body will also become very tall, and a very tall body means a very high center of gravity of the body. The high or low has a decisive influence on the handling performance, so too soft shock absorbers will cause handling obstacles. If the road is absolutely flat, then we don’t need springs and suspension systems.

If the road is rough, a softer spring is needed to ensure that the tire is in contact with the road, and the travel of the spring must be increased. The choice of spring hardness is determined by the ruggedness of the road. The more rugged the spring, the softer the spring, but how soft it is is a key issue. Usually this requires the accumulation of experience and is also an important issue for various car manufacturers and teams.

Generally speaking, a soft spring can provide better comfort and maintain better tracking performance when traveling on a rougher road. However, when traveling on general roads, the suspension system will swing up and down, which will affect the handling. In a car equipped with good aerodynamic components, the soft spring will cause the height of the car to change when the speed increases, resulting in different handling characteristics at low and high speeds.


The front suspension system of Xiaoqiu has two types of coil springs: 9 coils and 10 coils. The former is dedicated for 4-cylinders and the latter is dedicated for 6-cylinders. In the case of not increasing the front counterweight, generally there is no need to change the modification, just add a set of rubber pads. However, after replacing the front bumper and installing a winch, you must change the coil spring with more turns to ensure the controllability of the vehicle and the life of the related mechanical parts.