A spring rate is listed as a force/distance compressed. In the US where we still used pounds and inches, automotive springs are listed as lbs/in. So for every X amount of lbs you add or remove the spring will compress or raise Y inches respectively. Just for fun, lets say the stock springs are 1000 lbs/in. If we remove 1000 lbs from the front of the truck, the front will raise 1". This is an extremely simplified version of what is actually going on. Since our trucks use a torsion bar and IFS, you would really need to know the amount of rotation/lb the spring is rated at and measure the control arm swing radius. Like I said earlier, I don't know if a weak torsion bar is a little relaxed or settled but still has the same rate or if the rate is actually the same and the ends have simply rotated a little away from their original position.