Why are you replacing the springs? Springs tend not to wear out. If the purpose is for lowering, you're best off changing all 4 corners, and you should seriously consider changing your shocks for models that are a touch shorter. If you're using springs with a different spring rate than stock, it's imperative that you also change your shocks to something with correct valving.

 

I am changing the rear springs because my drivers side rear spring broke 1/2 a coil at the bottom.