I know how to calculate the spring rate thats physics. The question is what is the "real" spring rate not the "ideal" spring rate? Anyway, the easy option is to get a "standard weight" (in my case 100 lbs) and measure the distance the spring compresses. Voila! The spring rate! Anyway, the springs I got off ebay (6AA) had 3,000 miles on them, and the rate for them is 160lbs/in.