Hey guys, thanks for the UMI comments.
As a few mentioned above you want to make sure you get a-arms that feature some geometry changes in them, otherwise you're just stalling a-arms that look new and add no performance: no change no gain.
I can't speak for all a-arm manufacturers but here's UMI a-arms: Our goal is positive caster which increases steering feel, camber in turn and straight line stability. Caster is the angle of the spindle front to back, tilting the spindle rearward adds positive caster to the vehicle. In order to achieve this the UMI a-arms have the ball joint pads relocated increasing the vehicles positive caster. We move the lower ball joint cup frontward and the upper ball joint pad rearward. This tilts the spindle a few degrees to gain positive caster. By doing both together we keep the spindle pin centered in the vehicles wheel wells. On top of that I recommend a 1/2" taller ball joint which simulates spindle height, the tall ball joint changes the camber curve and keeps the tire patch on the ground more.
If you need any help the guys here at UMI are always willing to talk to help.
