Why aftermarket ball joints on lowered cars?

I have swift springs on my wagon. I also have the Whiteline bumpsteer kit (ball joints & tie rod ends).

Why is it recommended to go with an aftermarket ball joint on a lowered car? With the suspension lowered, the angle between the lower control arm and the spindle is less severe. Inherently, I would assume this would cause less stress on the ball joint versus a stock height car with more angle between the LCA and the mounting point on the spindle.

What am I missing?

it's not the stress on the ball joint, it's the geometry of the suspension.

on a macpherson strut car like ours, as your suspnesion travels through it's range of motion, the lower control arm can swing past parrallel to the ground. Just like a circle, once it's past that point, it only gets closer to the chassis as the suspension continues to compress.

This causes a dramatic negative impact on the handling of the car, and generally helps cause that nasty understeer we all love to hate by causing the camber to go positive under load. This is why race subarus that can't (or opt not to) use said ball joint spacers will often be only mildly lowered.

By using an extended ball joint on a lowered car, you help keep that control arm from passing the parallel point and keep your handling lively and good.

it's not the stress on the ball joint, it's the geometry of the suspension.

 

on a macpherson strut car like ours, as your suspnesion travels through it's range of motion, the lower control arm can swing past parrallel to the ground. Just like a circle, once it's past that point, it only gets closer to the chassis as the suspension continues to compress.

 

This causes a dramatic negative impact on the handling of the car, and generally helps cause that nasty understeer we all love to hate by causing the camber to go positive under load. This is why race subarus that can't (or opt not to) use said ball joint spacers will often be only mildly lowered.

 

By using an extended ball joint on a lowered car, you help keep that control arm from passing the parallel point and keep your handling lively and good.

Not a bad summary from a noob.

The issue of positive camber is important, but the REAL issue are the drastic changes in toe as camber changes.

Not a bad summary from a noob.

Title may say NOOB, but 8+ years of owning and tuning a national level prep STX WRX may have taught me a feeewww things about Subaru suspension.

I'm enjoying my new daily Legacy though.

That being said, i would disagree that the toe is the larger issue. Through the suspension stroke, the front end will toe out and that will typically enhance turning grip, but through only an inch of travel you can loose considerably more dramatic amounts of camber, causing the car to lift the inside of the tire, and overload the already overworked outer edges.

Title may say NOOB, but 8+ years of owning and tuning a national level prep STX WRX may have taught me a feeewww things about Subaru suspension.

 

I'm enjoying my new daily Legacy though.

 

That being said, i would disagree that the toe is the larger issue. Through the suspension stroke, the front end will toe out and that will typically enhance turning grip, but through only an inch of travel you can loose considerably more dramatic amounts of camber, causing the car to lift the inside of the tire, and overload the already overworked outer edges.

Remember that toe changes dynamically with camber AND wheel position. As you cycle camber, you are gaining and losing toe, and you are doing so at different rates and magnitudes for each front wheel.

Bumpsteer is caused by toe changes through wheel stroke.

There are really only two good ways to fix it. Modify the rear pickup (adding caster, which rotates the knuckle and brings the tie rod end back which decreases one component of misalignment as the wheel sweeps and reduces toe change). The other way, is to modify the front pickup, dropping the end of the control arm, and keeping that control arm within a range where camber doesn't sweep too wildly, taking toe along for the ride.

I've always gotten rid of bump steer by shimming the outer tie rod end where it attaches to the steering arm while monitoring toe with a bump steer guage.

That's what the tie-rod end component of the Whiteline RCK and GTSpec RCK's do.