Whiteline KCA313?
 

I have been told that these fit the BRZ/FRS. Can someone tell me at what point these become a good idea or a necessity when setting up your suspension? I assume they come into play when you change ride height, but at what point should one consider using these?

http://www.whiteline.com.au/product_...sans_vehicle=1

Bump... anyone?

one last bump before I let it fall into the abyss...

I've never used them, so take my information regurgitation for what it's worth.

The purpose of these is to restore the factory bump steer, camber curves, and roll resistance after you lower a strut suspension. You can make the statement that they are required whenever you lower your car. But they aren't adjustable like Robi's are so in reality they're pretty limited to the amount of lower they would work well with.

So this make the when part pretty subjective. RCE posted a while ago that they designed their yellows around the idea that these wouldn't be used. They did this by using front springs rates that would increase the roll resistance despite the car being lower, and keeping the amount of lowering to an area that would maintain good bump steer and camber curves.

That said, some of the other kits don't use springs as stiff as RCE and lower even more. Those springs may well benefite from the correction kit.

I just want to mention again that I haven't used these, but my understanding is that if you use this with most of the springs out there, these would have a similar effect to adding a slightly larger front sway bar. I'm saying that because within the range that most springs are going to lower the car, the bump steer and camber curves should be OK so the main effect will be roll resistance. If you're going to lower your a lot they'd probably take the car from being very squirly and unpredictable back to confidence inspiring.

They DO NOT fit. Ball joint is completely different.

However, just because they do not adjust does not mean they are only useful for a specific amount of lowering. Almost any amount of lowering is beyond what these correct for (~10mm) so really they are just making things "not as bad." The trouble with trying to correct with taller and taller spacers and ball joints is that it significantly increases the forces seen by the suspension upright. On Subarus I have seen the upright break at the ball joint due to a too tall roll center adjuster:

http://jamalb.net/gallery/d/2670-2/IMG_3119.JPG

The nice thing about these cars is that the ball joint is lower and in the control arm, so the geometry is already better off, plus the upright has more material and looks a bit stronger where the pin goes through compared to a Subaru.

Robi's kit looks like a pretty good choice if the car is low.