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With the coilover assembly removed from the car, all preload must be removed from the spring before recording any measurements. To accomplish this, the lower spring seat should be tightened just enough to remove freeplay from the spring. Accurately measuring the free length of the spring involves recording the distance from the upper spring seat slot to the bottom edge of the spring within 1/16-inch. This length may differ slightly from the spring's published free length. For instance, the 9-inch spring pictured here actually measures 815/16 inches. This will be used as the "F" value in the spring rate equation. Chassisworks recommends taking measurements for one front coilover and one rear coilover, as most production cars will have very little variation from right to left.