Concept for roll center correction. Fabricators and engineers please chime in.

how about something like this:



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really wish they made drop knuckles like they do for my iroc-z

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I'm surprised nobody has posted a diagram of a MacPherson strut roll center. I took this from my vehicle dynamics textbook. It will help you visualize what can be done to raise the roll center.

From the diagram you can see that you can raise the roll center in several ways after lowering:

1. raise inner joint
2. lower outer joint
3. Increase shock lean towards inside
4. increase track width (seems counter intuitive, can someone check that out)

Alright sorry I didn't post a diagram, was feeling under the weather yesterday.

I picked up some control arms, a 3.15 diff, fcab bushings, 23/18 sway bars and spindles to use as test subjects (I love having spares lying around).

I will post progress but a diagram first on some prototypes.

Don't know why you are apologizing. I saw that I could add some visual so I did .You can just take some measurements with very simple tools (tape measure and maybe an angle finder). Model that on some paper and calculate roll center changes for various mods. If I had the time I would make a model in solidworks for us, but I don't have the time for the measurements necessary. I can stress test models for you guys if you want though (however we don't know the forces to apply).

lowering ride height adversely affects roll couple it doesnt help it

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Originally Posted by IrocThe325i

lowering ride height adversely affects roll couple it doesnt help it

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It does lower the roll center, but I am not familiar with roll couple. Care to elaborate on it?

Originally Posted by IrocThe325i

is roll center effected by only the angle in which the control arm pushes against the inner bushings???

so if the control arm had a bend in it to counter the overall angle upward would that fix it?

orrr is it the point of force's height relative to the mounting locations of the control arm.

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No, has nothing to do with the angle of the control arms. It has to do with the position of the pivot points.

Originally Posted by IrocThe325i

how about something like this:

Attachment 472103

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Pretty much what I was thinking. I would use round stock because it's cheaper and more common. Not sure what the tiny holes would be for, if for a cotter pin or safety wire, that's not going to work. You also should make the threaded hole deeper so that it's easier to tap.

Originally Posted by WDE46

I'm surprised nobody has posted a diagram of a MacPherson strut roll center. I took this from my vehicle dynamics textbook. It will help you visualize what can be done to lower the roll center.

From the diagram you can see that you can lower the roll center in several ways:

1. Lower ride height
2. Lower innder joint
3. raise outer joint
4. Increase shock lean towards outisde (more vertical from picture I believe)
5. increase track width

The significance of the roll center can only be appreciated when the vehicle's center of mass is also considered. If there is a difference between the position of the center of mass and the roll center a moment arm is created. When the vehicle experiences angular acceleration due to cornering, the size of the moment arm, combined with the stiffness of the springs and anti-roll bars (anti-sway bars in some parts of the world), dictates how much the vehicle will roll. This has other effects too, such as dynamic load transfer.

Lowering the roll center relative to the center of mass increases body roll and suspension compliance. We are trying to raise the roll center to correct it after lowering it when we lower our cars.

Originally Posted by IrocThe325i

so this wont work?

Attachment 471815

No, while that changes the angle of the control arm, it doesn't change the position of the ball joints. The angle of the imaginary line drawn between the ball joint pivot points is the same.

Originally Posted by WDE46

I'm surprised nobody has posted a diagram of a MacPherson strut roll center. I took this from my vehicle dynamics textbook. It will help you visualize what can be done to lower the roll center.

From the diagram you can see that you can lower the roll center in several ways:

1. Lower ride height
2. Lower innder joint
3. raise outer joint
4. Increase shock lean towards outisde (more vertical from picture I believe)
5. increase track width

You want to raise the roll center, not lower it.

Originally Posted by mkodama

We are trying to raise the roll center to correct it after lowering it when we lower our cars.

Correct, you want to decrease the distance between the roll center and the center of gravity, known as the roll couple. Theoretically, if the roll couple is 0, then the car will have no body roll. But you have to remember the center of gravity and the roll center are always moving, therefore the roll center won't remain 0.

For a street driven car don't waste your time, spend the time/money on better dampers or more track time.

Originally Posted by vaio76109

No, while that changes the angle of the control arm, it doesn't change the position of the ball joints. The angle of the imaginary line drawn between the ball joint pivot points is the same.

You want to raise the roll center, not lower it.

Correct, you want to decrease the distance between the roll center and the center of gravity, known as the roll couple. Theoretically, if the roll couple is 0, then the car will have no body roll. But you have to remember the center of gravity and the roll center are always moving, therefore the roll center won't remain 0.

For a street driven car don't waste your time, spend the time/money on better dampers or more track time.

I think there is some effect when you get close to or beyond the point of no body roll, where the suspension becomes harsher and less compliant to bumps in the road, decreasing comfort and grip. Similar to anti-dive and anti-squat in the longitudinal directions when they are taken to far.

this is for a track car already on coilovers.

so i need lower the outer pivot point of the control arm and knuckle. so i have to either elongate the ball joint or knuckle...

neither of which seem to have an easy/safe method without major machining and engineering which makes me wonder why nothing has been created for our cars yet...

alot of us track them but maybe not enough.

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I'm gonna start emailing fabricating companies to make me a set of modified spindles/knuckles.

Should i get drop spindles or simply have them make a lower mounting point for the balljoint???

Alright here it is, sorry for the delay:



On the left:
Standard Alu control arm, when you press out the ball joint, a bearing cage needs to be installed using circlips to holy her in place. The spherical bearing is pressed into that and also held in place by circlips. A tapered pin is bolted into the tapered ball joint hole on the knuckle. Conical spacers are used to space the spherical bearing down from the control arm for proper alignment.

On the right:
Much simpler although heavier. Typical XI control arm. It is usable on all rwd 3 series. The ball joint end in the control arm is cut off and a receptacle for the spherical bearing is welded and braced in place. The spherical is either pressed into the receptacle or a spherical adapter is pressed in. Using the taper pin again with the conical spacers, you can then space the spherical down from the knuckle for proper control arm angle.

Pretty simple to do, isn't expensive or very time consuming, it just isn't in demand, hence the extravagant price of the kits that are sold.

I just picked this up today:


I ha e a spare set of Alu control arms now so I will be pressing the ball jojnt out and fabbing up a custom kit for my 323. I will also be fabbing up a set of rear upper control arm spherical bearing cages for peace of mind.

Originally Posted by mkodama

I think there is some effect when you get close to or beyond the point of no body roll, where the suspension becomes harsher and less compliant to bumps in the road, decreasing comfort and grip. Similar to anti-dive and anti-squat in the longitudinal directions when they are taken to far.

I'm just explaining the theory.

Originally Posted by IrocThe325i

this is for a track car already on coilovers.

so i need lower the outer pivot point of the control arm and knuckle. so i have to either elongate the ball joint or knuckle...

neither of which seem to have an easy/safe method without major machining and engineering which makes me wonder why nothing has been created for our cars yet...

alot of us track them but maybe not enough.

There have been solutions created for E46's, Bimmerworld makes one, I'm not sure if SLR does for the E46. My point is I think you're better off spending your money on other things first because I doubt you're running a good double(+) adjustable damper. This is coming from someone who has built and raced several E46's, including those with and without roll center correction. But what do I know?

Originally Posted by mkodama

Lowering the roll center relative to the center of mass increases body roll and suspension compliance. We are trying to raise the roll center to correct it after lowering it when we lower our cars.

I see. This makes sense. Just do the opposite to raise things then haha.

Originally Posted by vaio76109

I'm just explaining the theory.

There have been solutions created for E46's, Bimmerworld makes one, I'm not sure if SLR does for the E46. My point is I think you're better off spending your money on other things first because I doubt you're running a good double(+) adjustable damper. This is coming from someone who has built and raced several E46's, including those with and without roll center correction. But what do I know?

i just cant bring myself to spend that much money on parts i may destroy. not at this point in my life at least. just want it to be more fun to drive hard then stock. if i had an m3 id probably leave it oem.

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Originally Posted by drift.mechanic

Alright here it is, sorry for the delay:

Attachment 472267

On the left:
Standard Alu control arm, when you press out the ball joint, a bearing cage needs to be installed using circlips to holy her in place. The spherical bearing is pressed into that and also held in place by circlips. A tapered pin is bolted into the tapered ball joint hole on the knuckle. Conical spacers are used to space the spherical bearing down from the control arm for proper alignment.

On the right:
Much simpler although heavier. Typical XI control arm. It is usable on all rwd 3 series. The ball joint end in the control arm is cut off and a receptacle for the spherical bearing is welded and braced in place. The spherical is either pressed into the receptacle or a spherical adapter is pressed in. Using the taper pin again with the conical spacers, you can then space the spherical down from the knuckle for proper control arm angle.

Pretty simple to do, isn't expensive or very time consuming, it just isn't in demand, hence the extravagant price of the kits that are sold.

I just picked this up today:
Attachment 472271

I ha e a spare set of Alu control arms now so I will be pressing the ball jojnt out and fabbing up a custom kit for my 323. I will also be fabbing up a set of rear upper control arm spherical bearing cages for peace of mind.

Do Xis use the same fcab's??

are they stronger than the aluminum ones??

im considering modifying a set like the drift 240 posted above.

what makes the spherical stud stronger than the extended ball joints in relation to shear strength???

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Think about how much a good set of coilovers are, way more than a roll center correction kit and they get easily destroyed.

I think the issue with selling roll center kit is because they don't offer a huge performance gain like other parts would for the same money (ie; 1500$ roll center kit, vs 1500$ with of NT01 Tires and rims).

The buyer will always lean to getting the best bang for buck. After their suspension is pretty much all taken care of with poly bushings and adjustable arms, a roll center kit should follow, right? Right if you want to do it right,
Wrong if you take the roll center kit fund and sink it into a Dynavin or equivalent waste of money.

A suspension system is a system and not individual components. Every single part of the suspension works in harmony to produce a desired, precise steering control, comfort and stability over un even roads and so on.

If you have a complete system and chose to not invest in a roll center correction kit for the lower tables and tie rods, congrats on wasting all that cash on parts you will never use to their fullest. Not to mention, enjoy the dangerous bump steer, binding ball joints and other lovely problems you created by not seeing the suspension mods to the end.