When you lower your car the roll center point gets misaligned with the sprung center of mass/center of gravity. This upsets the steering geometry which results in bump steer. In plain English: Lowering your car past a certain point can have the unwanted side effect of losing straight line stability. Rather than inherently tracking straight you will find that your car is following cracks in the road and you are having to put more effort into driving in a straight line.
The solution to this issue is typically extended ball joints and sometimes also extended tie rod ends. These aftermarket components correct the geometry changes and optimize the positioning of the roll center point.
At Cygnus Performance we have been selling roll center correction/bump steer kits since 2006. Unfortunately good brands have come and gone, and the quality of options that was previously acceptable has gone downhill. We are actively working on finding or manufacturing better quality solutions, but for the time being we offer Whiteline. SuperPro merged with Whiteline in 2019. We prefer the Whiteline version because we have seen less issues with ripped boots compared to SuperPro recently and Whiteline is backed by a big distributor who picks up the phone if there is a problem. It’s not really a product that we can fully vouch for though. From what we have seen the longevity of OEM ball joints and tie rod ends seems to be better than these aftermarket options. We are advising our customers to skip this mod unless they are lowering their car more than 1.5″ or unless they notice bumpsteer that needs addressing. We would make more money if we continued to recommend all of the supporting mods, but our reputation has been earned by providing our honest, candid opinion. Stay tuned.