My equations come from "Racecar Vehicle Dynamics" by Bill and Doug Milliken, they refer to it as installation ratio on P595. You can define it as the inverse as some books do, however you need to change your wheel rate equation to match. WR=SR*(MR)^2 if MR is less than 1 like Milliken defines it, WR=SR/(MR)^2 if MR is greater than 1 like Carroll Smith defines it. An easy way to check to make sure you have it right is to make sure your wheel rate calc is less than your spring rate.