In most cases when building a custom vehicle, individuals might not have their vehicle weight and or know where to start. Coilover spring are not cheap to purchase so its best to obtain 1 set of springs for your coilovers and use those to determine how much weight you have on top of the coilovers. Here is a basic guide to using a spring to tell you how much weight you are holding with your coilovers.
Lets look at an example of using a 14" 700Lb spring. If we set the vehicle down onto the coilovers with the spring installed and we see 2" of compression lets do some math.
To calculate the force required to compress a 14" 700lb spring to 12", you would need to use Hooke's Law, which states that the force required to compress or extend a spring is directly proportional to the displacement or change in length of the spring. The formula for calculating the force required to compress a spring is: F = k * x where:
F is the force required to compress the spring
k is the spring rate (in units of force per unit of displacement, such as pounds per inch)
x is the change in length of the spring (in units of length, such as inches)
In this case, the spring rate is 700 pounds per inch (lb/in), and the change in length is 2 inches (from 14" to 12"). So, we can calculate the force required as follows: F = k * x F = 700 lb/in * 2 in F = 1400 lb Therefore, it would take 1400 pounds of force to compress a 14" 700lb spring to 12". It's important to note that this calculation assumes that the spring is being compressed evenly and there are no other factors, such as friction or binding, that would affect the amount of force required.
Now that you know you have 1400lbs of sprung weight on that specific coilover, you can calculate your spring rate using this formula.