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Suspension & Braking
Have some questions about suspension or brake setups for your E46 BMW? Get all your answers here!

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Old 09-29-2012, 07:36 PM   #1
IrocThe325i
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Concept for roll center correction. Fabricators and engineers please chime in.

Okay, so, as most of us know over lowering a car with a Macpherson strut suspension design causes poor roll center. Poor roll center means that regardless of how low you go you will not reduce body roll as expected. Lowering does lower center of gravity but that doesn't mean sh*t if the end of your control arms are pointing upwards at a 60* angle.

So heres an idea that seems pretty simple which makes me believe i'm over looking something substantial.

On the Knuckle (spindle/hub) Why can't you extend the little arm that protrudes downward where the ball joint bolts through? If you cut it and welded an inch and a half or so and gusseted the arm, leaving room for the balljoint bolt of course, would it crack off and cause you to flip and burn to death???

Im trying to find a diagram to modify to help provide a better explanation of what im talking about.

Im considering having my fabricator friend modify a set of knuckles and test it out. Although i rather use a beat up old e46 than mine.

All you people that are most likely smarter than me, throw some input my way and tell me why or why not.
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Old 09-29-2012, 08:29 PM   #2
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Draw it up in AutoCAD and run a projection.
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Old 09-29-2012, 08:37 PM   #3
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This is a question you'd have more luck getting an answer to in the track section at bimmerforums.com.

http://forums.bimmerforums.com/forum...play.php?f=128

Last edited by Bayerische E46; 09-29-2012 at 08:43 PM.
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Old 09-29-2012, 08:45 PM   #4
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DO NOT MODIFY THE SPINDLE

If you want to roll sender correct your control arm, you have 2 choices:

1- Instead of having a ballpoint at the end of the control arm bolting to the spindle, have a spherical bearing installed. Fabricate a long bolt that has the same taper as the OEM ball joint to fight snugly in the tapered orifice. Using a conical spacer and tubular "pipe shaped" spacers until the desired angle of the control arm is achieved. The bolt must be long enough to go completely through the spherical bearing, pass through another conical spacer, to allow full movement of the bearing, then cap it off with a castle nut and cotter pin.

2- Fabricate a offset bar to bridge the 2 tapered holes of the ball joint and tie rod. The bar has to be the correct height to correct the angle of the control arm since it is not adjustable. 2 tapered holes have to be drilled in the bar, relocating the tie rod and ball joint lower towards the ground than before. Generally this setup is used in drifting where they try to achieve more steering angle by relocating the tie rod pickup closer to the center of the spindle, thus giving you reduced steering feedback but increasing steering angle (changed the fulcrum of the tie rod assy).

Hope this helps, but don't modify the spindle, it's only a matter of time before it cracks, regardless of how good the welder is.

If you want picture examples of what I'm talking about, visit Driftworks website and lookup their Geomaster knuckle kits for Nissan 240sx/Silvia.

Good luck.
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Old 09-29-2012, 08:48 PM   #5
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^ +1. I was going to add that you could apply a similar principle to what racers do to correct bump steer (i.e. mechanically spacing the pivot point downwards instead of cutting/welding a knuckle). There it is.

OP, check out this link:
http://www.modified.com/tech/0508_sc...3/viewall.html

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Old 09-29-2012, 09:26 PM   #6
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Yessss perfectt!!!!
Click image for larger version

Name:	uploadfromtaptalk1348972015021.jpg
Views:	406
Size:	77.9 KB
ID:	471674

but how would this work for an aluminum control arm?



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Old 09-29-2012, 09:55 PM   #7
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Yessss perfectt!!!!
Attachment 471674

but how would this work for an aluminum control arm?



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Um, seeing that we're talking funky angles, I wouldn't trust an aluminum control arm that's designed virtually flat. On my racecar, or on any car, I would only adopt something like that if I had a custom-built steel control arm.

In the photo you posted, look at the arm - it's still and look how much reinforcement was done to it. I wouldn't even consider aluminum.

Last edited by Bayerische E46; 09-29-2012 at 09:56 PM.
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Old 09-29-2012, 11:17 PM   #8
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Honestly there is no issue using an aluminum control arm. Problem would be the angle if the tip of the control arm (specifically the portion where the ball joint is). I doubt the original control arm would have the correct angle without modifying it. Only way to know would be to try, I'm game so if someone has a control arm they replaced hanging around, I'll through a spherical on it and have a look.

Realistically speaking though, to utilize the spherical roll center corrected ball joint, you would also need to use the roll center corrected tie rod (which requires 17" rims minimum). Now that you're getting into heavy mods, the aluminum probably won't keep up with the stronger steel or chromoly replacements. So you would fab up a tubular steel replacement. Since you're going through all this trouble, might as well convert the inner ball joint to a spherical a well. Since all that work has been done, might as well use the 3 point OEM design and integrate a fully adjustable caster portion into the tubular arm.

Change one thing, 10 more follow, especially when you're messing with something as touchy as roll center correction.
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Old 09-30-2012, 02:23 PM   #9
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Originally Posted by drift.mechanic View Post
Honestly there is no issue using an aluminum control arm. Problem would be the angle if the tip of the control arm (specifically the portion where the ball joint is). I doubt the original control arm would have the correct angle without modifying it. Only way to know would be to try, I'm game so if someone has a control arm they replaced hanging around, I'll through a spherical on it and have a look.

Realistically speaking though, to utilize the spherical roll center corrected ball joint, you would also need to use the roll center corrected tie rod (which requires 17" rims minimum). Now that you're getting into heavy mods, the aluminum probably won't keep up with the stronger steel or chromoly replacements. So you would fab up a tubular steel replacement. Since you're going through all this trouble, might as well convert the inner ball joint to a spherical a well. Since all that work has been done, might as well use the 3 point OEM design and integrate a fully adjustable caster portion into the tubular arm.

Change one thing, 10 more follow, especially when you're messing with something as touchy as roll center correction.
please see if u can manage this id definetly buy it!!

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Old 09-30-2012, 02:39 PM   #10
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how do these change roll center?

http://store.bimmerworld.com/mobile/...StoreType=BtoC

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Old 09-30-2012, 03:15 PM   #11
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Those control arms use spherical bearings, pins for the tapered holes and conical spacers for the offsets. Exactly what I was talking about.

Pretty simple to do, and inexpensive.
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Old 09-30-2012, 03:48 PM   #12
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The car in my sig had the roll center changed. Just a machined piece to move the pivot point of the control arm lower. The same thing was done with the tie rods to fix bump steer. The catch was that 18" wheels were required to clear the newly relocated suspension pieces.
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Old 09-30-2012, 04:02 PM   #13
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If anyone has a pair of OEM arms, I can play with them and slap in a set of sphericals.

Let me know.
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Old 09-30-2012, 04:11 PM   #14
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And yes 18" rims are required. The ken tie rod has a small bend in it so when you turn the wheel to full lock, the inside of the rim doesn't hit the tie rod. With 18" wheels and a roll center corrected heim joint tie rod, the wheel clears the straight tie rod.

Using spherical bearings as ball joints in the control arms instead of actual ball joint, you would never need replacements (if mil spec is used) and they would be 100% adjustable. So every time you do something on your suspension, a quick measurement at the alignment shop, a shim or 2, then bingo, perfect alignment for the best suspension behavior and handling.

Basically roll center adjustment is to retain OEM geometry when lowered, widened or raced when slammed.

The car behaves the best using OEM geometry, and slamming the car without roll center adjustment actually kills the OEM geometry causing bump steer, bushing binding and so on.
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Old 09-30-2012, 04:14 PM   #15
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i cant run 17s with a bumpsteer kit?

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Old 09-30-2012, 04:17 PM   #16
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I think you could. With the proper offset, yes
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Old 09-30-2012, 04:20 PM   #17
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So if I were to start producing a roll center toe rod fit for E46 sub 250$ (that is the going rate for other kits), I'm guessing there would be significant interest.

If there is enough interest, I can produce them.
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Old 09-30-2012, 04:21 PM   #18
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So if I were to start producing a roll center toe rod fit for E46 sub 250$ (that is the going rate for other kits), I'm guessing there would be significant interest.

If there is enough interest, I can produce them.
there are other kits??? for e46s???

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Old 09-30-2012, 04:25 PM   #19
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There are kits, SLR is 260$ (for tie rods) and UGR is 299$ (for tie rods).

The average roll center kit for the ball joints is 900$-1400$ that includes everything.
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Old 09-30-2012, 04:27 PM   #20
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There are kits, SLR is 260$ (for tie rods) and UGR is 299$ (for tie rods).

The average roll center kit for the ball joints is 900$-1400$ that includes everything.
send me a roll center correction kit link im in desperate need of one!

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