Originally Posted by astroracer
One of several reasons would be geometry.
Yes, that's a given. In the case of the Pinto (aka Mustang) spindle with the Sprite, it appeared that the guys at Ford had the Sprite in mind. Everything fell right into place with the Sprite steering matching up perfectly. As I used a tubular aftermarket upper arm (the shock serves as the stock Sprite upper arm), I was able to place the roll center exactly where I wanted.
I've suggested arm splicing for those cars where dropped spindles are not available and a lower stance is desired. In this case, there could be a significant geometry change, with the roll center usually going lower. This would make the car a bit looser, but that is usually a "plus."