Suspension system is one of the most important systems in a car, responsible for a comfy and balanced ride. However, suspension system does not necessarily means only the springs itself, it also includes tires, tire air, springs itself, and shock absorbers.
Besides serving as a way to keep occupants comfortable, Suspension system also contributes to the vehicle’s roadholding, handling and also braking for safety and increase driving pleasure. Suspension system also increases ride quality reasonably well by reducing road noise, bumps and also vibrations on the road. It is important for the suspension system to make sure the tyre keeps a good contact with the road as much as possible, as all road forces acted on the vehicle is done by the contact patches of the tyre.
The idea of increasing comfortability when using a four wheeled begin in the early 17th century, with automobile of that time initially developed as self propelled versions of horse drawn vehicles. And its ability cannot suit the higher speed and more powerful torque of internal combustion engines.
Modern suspension system is calculated by spring rate, which is defined as component in setting the vehicle’s ride height or its location in the suspension stroke. When a spring is stretched or compressed, its exerted force is proportional to its change in length. The spring rate, or also known as spring constant of a spring is the change in the force it is able to exert, devided by the change in deflection of the spring. Vehicles that carry heavier loads often will have heavier spring some companies like BC Racing also offer custom spring rates on coilovers systems they sell. When compared to vehicles that carry lower weight as they need to compensate for the extra weight that could otherwise collapse a vehicle to the very bottom of the spring’s travel. Heavier springs are also often used in performance application where the loading conditions is no longer weight inside the car, but instead the very extreme G- force exerted by performance cars.
Choosing springs will be a hard choice as too hard or too soft of a spring will cause the suspension system to decrease in effectivity as they fail to isolate the vehicle from the road. Vehicles that always experience suspension overload have springs that are too hard or too heavy that is closer to the upper limit for that particular vehicle’s weight. This can allow the vehicle to perform properly under a heavy load when there is control limited by the inertia of the road. Occupying an empty truck used for carrying heavy weights might be uncomfortable for passengers because of the higher spring rate, when related to the weight of the vehicle. Race car that are very light also will have heavy springs that makes occupants uncomfortable. Even though they have heavier springs, actual spring rate for a 910kg race car and a 4500kg truck is very different. The springs used in luxury car, taxi or bus would b described as soft.
Spring travel is also one thing to consider, as pickup trucks will have springs that can travel much more further than that of a race car. This is such because pickup trucks usually have more off roading experience, thus longer spring travel is needed to combat those high mountains and uneven road unlike the race car as it is mostly done on tarmac surface.