Springs and ride height are quite possibly the easiest setup elements to understand, so it makes sense to start here. Springs are also the absolute foundation of your setup.
Rear coil spring with bump stop visible
Coil over springs and dampers
As mentioned, springs are the foundation of your setup. But what do they do and how do I use that make my car perform?
Quite simply, the springs are what support your car above the wheels, and also what allow the wheel to move under the car to adapt to the road surface. Sounds simple right? WRONG. That's only the half of it. Changes to any part of your car will impact the springs, and changes to the springs will impact how the car handles.
As you can see from the images above, there are different types of springs for different applications and cars. Some cars will feature coil springs with the dampers installed separately, and other cars will feature what are called "Coil Over" springs, where the spring and damper are one unit. For the purposes of this section, we will discuss the springs as a stand alone unit. We'll cover dampers in a later section.
So, what exactly do the springs do, and how do we tune them?
Well, let's first make sure we understand what the springs are doing for us. As mentioned, they are supporting the weight of the car above the wheels, and also allowing the wheels to move in response to the road surface. Why is this important?
We've all seen the movie scenes where wagons like this end up bouncing and bucking all over as the horses bolt off.
That's because these wagons had no springs in their undercarriage. Notice the springs for the "comfortable ride" were actually between the seat and the wagon chassis.
Without springs between the axles and the chassis, every time the wheel hits a bump or a hill, it forces the entire wagon chassis to react. This might not be a problem at slow speeds, but at high speeds it can be catastrophic. Just like that scene in the movie.
Springs allow the wheels to move and react to the road surface independant of the chassis, while still supporting the chassis. Springs also affect the handling of the car. Let's talk about that for a minute.
Spring Rate refers to the stiffness of the spring, or more accurately, the amount of weight needed to deflect the spring 1 inch. The lower the number, the softer the spring is. When it comes time to determine our spring rate, we have a significant number of factors to consider, as follows:
The term mechanical grip, refers to the amount of grip the car itself has directly from the tires and suspension. This means without any external forces added, such as aerodynamic help from diffusers, wings, sideskirts, etc.
The springs play the primary role in determining the level of mechanical grip in the car. As the car's setup changes to address certain issues, this mechanical grip will also change.
As a general rule of thumb: