I see that a lot of the online apps don't mention, or "skim over", the total working angles that includes the top view compound angle. This has to be added in the equation but is difficult to measure. Our cars have the rear offset to the passenger side, some more than others, and a reason why some cars fight more drive line vibrations more than others. Tossing in the pinion shims is great to get everything equal and opposite & parallel on the hit, great if drag racing all the time, but what is the angles at at steady driving. (Just what XTEN is saying) Use soft springs & bushings and your just running in circles. I've used 7* pinion angle on the "drag setups" and loaded the angles are close to "0", just what I want, but would not use that on the street all the time.