Suspension modification is the first step for most people when they modify their beloved cars. The modification of suspension usually starts with replacing the shock absorbers with a harder set. Below, we will introduce the shock system that is very important for vehicles.
The existence of the shock system serves two purposes: one is to buffer the unevenness of the road and make driving more comfortable; the second is to maintain contact between the tires and the ground while driving on uneven roads. For enthusiasts, modifying the shock system has only one purpose - to improve handling. Before discussing the shock absorber, let's talk about the springs first, which are easier for everyone to understand the shock system.
Since there are too many things in this part that we do not need to understand, I will try to express the core principles with the simplest words. Now, the most common type of spring used in suspension systems is the coil spring, mainly because it is easy to manufacture, performs efficiently, and is inexpensive. In traditional spring and shock absorber designs, the spring plays a role in supporting the body of the car and absorbing the impact caused by uneven roads and other forces applied to the tires, including acceleration, deceleration, braking, turning, etc. More importantly, during the process of eliminating vibrations, it maintains continuous contact between the tires and the road, maintaining the car's traction. How to improve continuous contact is the primary consideration in modification and tuning.
Springs themselves also have different levels of stiffness based on the materials used in manufacturing. When modifying, if you use too stiff springs, the car may bounce when encountering uneven roads, losing friction between the tire and the ground. On the other hand, if you use too soft springs, they can be easily compressed, causing the shock absorber's travel to be fully utilized, making it easy to lose traction when turning. Therefore, when choosing springs, it depends on the road conditions: the flatter the road, the stiffer the springs you can use, and the bumpier the road, the softer but longer-travel springs you should use. There is another type called "progressive springs," which increase the spring rate as the spring compresses, but due to the difficulty in manufacturing, they are uncommon, so we won't discuss them here.
Finally, let's talk about the spring constant K value, which is a parameter for judging springs. The spring constant K refers to the elasticity coefficient of the spring, measured in kgf/m. The higher the K value, the stronger the energy stored when the spring is compressed.
We mentioned earlier that the main function of the spring is to eliminate vibrations from uneven roads. Since we already have springs that can eliminate vibrations, what is the purpose of the shock absorber? The shock absorber is not used to support the weight of the body but to suppress the oscillations after the spring absorbs the shock and to absorb the energy from road impacts. If you've ever driven a car with broken shock absorbers, you would understand the lingering bouncing sensation after every pothole or bump. The shock absorber is precisely used to suppress such bouncing. Without shock absorbers, it would be impossible to control the rebound of the springs, causing severe bouncing when encountering rough roads and loss of tire grip and traction when cornering. The ideal situation is to use the shock absorber to limit the spring's bounce to just once.
When we compress or stretch the shock absorber at a fixed speed, the resistance generated is called damping. This resistance comes from the operation of the shock absorber, where the piston pressurizes the damping oil, forcing it through small-aperture valves. Changing the valve aperture can adjust the size of the damping. Most modified shock absorbers provide this feature, allowing the owner to automatically adjust the softness and hardness. The resistance of the shock absorber can be divided into compression and rebound parts. Compression resistance complements the hardness of the spring, increasing the strength of the spring when in operation. Rebound resistance occurs during the rebound stroke after the spring is compressed by road impacts. This is the biggest reason for the existence of the shock absorber - it resists the force that pushes the tire back to the ground after the spring is compressed, reducing the rebound impact and maintaining vehicle stability. Generally, for road-use shock absorbers, the damping resistance during compression is much less than during rebound. This is because too much damping resistance during compression affects ride comfort. For road vehicles, the ratio of damping forces during compression and rebound is approximately 1:3, but for racing cars, it ranges from 1:2 to 1:1.5. A higher ratio reduces comfort but improves traction on irregular roads. The speed of weight transfer (Weight Transfer) during corner entry and exit affects handling balance, and this influence continues until the weight transfer is completed. The speed of weight transfer is controlled by the shock absorbers, and changing the speed of the shock absorber during compression and extension can change the speed of weight transfer. The harder the shock absorber, the faster the weight transfer, and the faster the weight transfer, the quicker the vehicle's steering response.
Since steering response is crucial for handling, we hope to establish cornering posture as quickly as possible, but not too fast. There must be time for the driver to feel the establishment of the cornering posture and perceive the limit of traction. If the weight transfer is too fast, the driver won’t have enough time to sense it. Therefore, setting an appropriate speed for weight transfer so that the driver can feel the approach of the limit and respond accordingly is an important issue in vehicle suspension setup. We often say that teams will have different vehicle setups depending on different drivers. For suspension system settings, different drivers, due to differences in driving techniques and habits, will have different feelings and reaction speeds regarding steering responses, thus requiring different suspension setups to maximize the driver’s performance.