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Extended ball joints and bump steer

Old 4/25/18, 05:24 AM
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Extended ball joints and bump steer

** if you don't want to read all the background, skip to 2nd-to-last line **

My 2010 GT is lowered about 1" in the front on Steeda Sport springs, has almost 100,000 miles on it, and it's getting to be time for ball joints. Also I want to stiffen up the bushings in the front lower control arms.

I am told that lowering the car changes the roll center which is not desirable for cornering/handling and that can be corrected with extended ball joints (someday I'll have to do the research to understand how that all works). Steeda sells A-arms with the ball joints and bushing already installed, making them a fairly easy unbolt/rebolt installation.
https://www.steeda.com/05-10-mustang...-777-4902.html

At the same time, these cars have issues with "bump steer" which means the toe changes as the suspension travels; which means the wheel is being turned by the suspension not the steering wheel which produces some undesirable handling also. This gets worse when you lower the car because the geometry of the steering system is altered. On the street this "bump steer" happens on bumps but on the track it happens as the car rolls in a corner. This can be (mostly) corrected using modified outer tie rod ends:
https://www.steeda.com/steeda-mustan...-555-8106.html

Right now with the factory ball joints; and I guess I do have bump steer but I don't notice it in any big way; maybe just used to it.

Now that I got all the background out of the way, here's my issue and question:

I think I read that the extended ball joints make the bump steer worse and this requires correction with the bump steer kit; or maybe I misunderstood. There was a post on here a while back where one of the guys got BMR's A-arms with extended ball joints and said it screwed up the steering/handling of his car and I wonder if this had something to do with it.

So this is making me question whether I really want those extended ball joints . . .

** Can anyone here clarify this issue; do the extended ball joints make the bump steer worse and what's the best solution for all this?

thanks in advance

Last edited by Bert; 4/25/18 at 06:11 AM.
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Old 4/26/18, 09:07 AM
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updating my own thread and sending it back to the top:

Some folks who sound very knowledgeable and experienced, in a certain FB group, are advising that the extended ball joints cause the bump steer issues; and the extended ball joints really are not recommended for a street/track car.

I think the above probably explains the problem that the other guy reported in the "track related mods" thread a while back. (haven't taken the time to find it and refresh my memory)

So now I am looking at replacing the ball joints with normal ones and the bushings with poly, dreading the thought of removing the old bushings, but the good news is the cost for the parts is a lot lower.

any addition thoughts, comments, experiences, suggestions welcome!
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Old 4/26/18, 12:22 PM
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Hey John, I can't contribute much here as my steering geometry knowledge is lacking at best.

I can tell you a bit about the effect my mods had on steering. After loweing and adding a front sway I need to put in ~15-20 degrees more steering to get the car to turn off center. I was also wondering if this is because lowering of the roll center.

I did nothing to adjust for this tho, and I just live with it. I have not noticed more bum steer or any other adverse effects.

Good luck and keep us posted.
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Old 4/27/18, 08:54 AM
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Thanks Marty (hey I remembered!) 15-20 degrees seems like a lot . . .

I found that old post, it was "redonblack" who installed the BMR A-Arms with the extended ball joints and it wacked out the geometry of his front end big time. So I guess the FB gang is right, this is not a good mod! I guess the extended ball joints are for more extreme lowering like 1.5" or more but I'm still surprised that it could cause such a mess.

So now I'm trying to decide if I will fight with the old bushings, or spend $500+ for the BMR A-arms with the normal height ball joints and bushings already installed.

Last edited by Bert; 4/27/18 at 08:55 AM.
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Old 4/27/18, 07:02 PM
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Originally Posted by 5.M0NSTER View Post
Hey John, I can't contribute much here as my steering geometry knowledge is lacking at best.

I can tell you a bit about the effect my mods had on steering. After loweing and adding a front sway I need to put in ~15-20 degrees more steering to get the car to turn off center. I was also wondering if this is because lowering of the roll center.

I did nothing to adjust for this tho, and I just live with it. I have not noticed more bum steer or any other adverse effects.

Good luck and keep us posted.
This may have more to do with the stiffer sway bar than the lowering springs. A stiffer front sway bar in relation to the rear typically with induce more understeer.
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