The purpose of a suspension system is twofold: to isolate uneven road surfaces for a more comfortable ride; and to maintain tire contact with the road when driving over uneven surfaces. For speed enthusiasts, improving the suspension has only one purpose: to enhance handling.
Coil springs are the most common type used in suspension systems because they are easy to manufacture, highly efficient, and inexpensive. In physics, a spring is defined as a stored energy source. When a fixed force is applied to a spring, it deforms. When the force is removed, the spring tends to return to its original shape. However, the amplitude of the spring's rebound often exceeds its original length. Frictional resistance is needed to slow down the free oscillation caused by the spring's rebound. This slowing down of the spring's free oscillation is usually the task of the shock absorber. A typical spring is a so-called (linear spring), meaning that when a spring is subjected to force, its compression deformation follows Hooke's Law: F=KX, where F is the applied force, K is the spring constant, and X is the deformation. For example, a linear spring will compress 1 cm when carrying a 40 kg weight; for every additional 40 kg of weight, the spring will compress by 1 cm. In fact, the suspension springs also experience additional pressure. Even when fully extended, the springs are still under pressure to keep themselves fixed to the car. In traditional spring-and-shock-absorbing suspension designs, the springs support the car body and absorb the impact of uneven road surfaces and other forces on the tires. These other forces include the forces exerted on the springs by acceleration, deceleration, braking, and cornering. More importantly, they must maintain continuous contact between the tires and the road surface during vibration damping to maintain the car's traction. Improving tire-road contact is a primary consideration for improving handling. The spring's main function is to maintain the car's comfort and keep the tires in full contact with the ground. Using the wrong springs will negatively impact ride quality and handling. Imagine if the springs were completely stiff; the suspension system would be ineffective. When encountering uneven surfaces, the car would bounce, and the tires would completely leave the ground. If this happens during acceleration, braking, or cornering, the car will lose traction. If the springs are too soft, the car is prone to bottoming out, meaning the suspension travel is exhausted. If a car bottoms out while cornering, it can be considered that the spring's coefficient of motion becomes infinite (there's no room for compression), causing an immediate weight transfer and loss of traction. If the car has a long suspension travel, bottoming out might be avoided, but the car will also be very high. A high car means a high center of gravity, which has a decisive impact on handling performance. Therefore, overly soft shock absorbers will hinder handling. If the road surface is perfectly flat, then springs and a suspension system are unnecessary. If the road surface is rough, softer springs are needed to ensure tire contact with the road, and the spring travel must also be increased. The choice of spring stiffness depends on the road roughness; the rougher the road, the softer the springs.
However, how soft is "too soft" is a crucial question, usually requiring accumulated experience and is an important topic for car manufacturers and racing teams. Generally speaking, softer springs provide better comfort and maintain better traction when driving on rougher roads. However, when driving on ordinary roads, this can cause significant vertical swaying of the suspension system, affecting handling. In cars equipped with good aerodynamic components, soft springs cause changes in vehicle height as speed increases, resulting in different handling characteristics at low and high speeds.
