Rob can correct me if I'm wrong, but I believe you're referring to what they call the king-pin inclination angle.....the angle you get when you draw a line through the upper and lower ball joints to the ground....if you're making your own spindles, and know your wheel and tire size, you can determine the ideal king-pin angle. Ideally, you want the imaginary line drawn through the ball joints to hit the ground at the center of the tread on the tire, that reduces the scrub angle when you turn and will also reduce steering effort.....clear as mud?
Rob might be able to explain it better than I can
