All stock S197 Mustangs have the stiffer spring in the rear of the car. Without considering the weight distribution and the motion ratio of the spring, the actual rate is meaningless.
To get the rear resonant frequency 10-20% higher than the front, the rear wheel rate usually needs to be higher than the front.
To get the rear resonant frequency 10-20% higher than the front, the rear wheel rate usually needs to be higher than the front.
