Springs support the weight of the car and are generally specified in pounds of force required to deflect (compress) the spring 1 inch, also known as spring rate. The higher the number the firmer/stiffer the spring. Springs that take a linear amount of force to deflect are called linear springs while progressive springs take less force to deflect initially and take more force to continue deflection as the spring is compressed. Progressive springs are popular with performance enthusiasts as they provide a more comfortable initial spring rate with a firmer final spring rate that keeps the vehicle more stable. A good way to think about springs is to remember that they limit how far the suspension moves, not how fast.