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

31K views 89 replies 11 participants last post by  IrocThe325i 
#1 · (Edited)
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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#45 ·
Don't know why you are apologizing. I saw that I could add some visual so I did :thumbsup:.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).
 
#53 ·
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.

Not from my iphone
 
#55 ·
Alright here it is, sorry for the delay:

Text Drawing Design Line Font


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:
Auto part Metal


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.
 
#59 ·
Alright here it is, sorry for the delay:

View 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:
View 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???

Not from my iphone
 
#60 · (Edited)
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.
 
#62 ·
Yeah the inner ball joint are different, but the outside dia of the ball joint unit is the same. The length of the control arm from the inner bj to the outter bj is different, but that needs to be cut anyways.

The XI control arms are perfect for chopping and welding, nice and strong cast iron. Easily machined too should it require it. (Much simpler to modify the bolt it cast piece than fab a tubular arm, but the bonus of tubular is adjustable caster)
 
#64 ·
Yes I will convert both. It isn't a absolute must since no binding will occur with a perfectly flat lower control arm. For reliability on the other hand, I would convert the ball joint to spherical just like the outter.

Now there is also the ease of replacement (with no alignment since their machining tolerances are in 1/10000" in MIL spec bearings), adjustability of the inner and outter with 1/1000" precision, constant adjustment for track then street (with about 10 mins of work), and the list goes on.
 
#66 ·
It's going to be close to Jan 1.
In the works now is a set of tubular spherical control arms with built in roll center correction for Honda/Acura, roll center tie rods for Civic/Integra, eye mount conversion and extended top plates for Civic/Integra (I do many SCCA and CTCC cars as you can see).

It's going to be a while, but I'll get it done
 
#73 · (Edited)
even the bimmerworld race spindles for e36s are welded. Alot of race bmws seem to be using modified spindles usually for the spherical style end. I dont see why i can't build a set to use a streetable generic control arm with a balljoint

im simply going to extend the ball joint seat location without removing the current location but instead drill it out to be able to fit an impact in it. Lots of gusseting and reinforcement prolly a good deal of it overkill but that makes me feel better :)

heres the motorsport setup using a PTG kit or something:
 
#79 ·
Ah gotcha. I drift so the increased steering angle was a must for me, and the fact that this kit does/includes so much more made it worht the investment. His work is absolutely on point and he really knows his stuff. I do recommend calling him directly (emails with him sometime take a bit) .
 
#87 ·
Working on search engine optimization here and the roll-center search brought this thread up, so I figure I'd throw some info here.

Our roll-center correction kit for the E46 gives 28mm of correction and matches the bump-steer at the same time 9saving you having to get a separate bump-steer kit). It also quickens the steering and fits in smaller wheels than any other kit out there.

On top of that, you can adjust the bump-steer and roll-center further with shims if you like, and you also get 5 different ackerman positions. (ackerman defines how much more the inside wheel will turn than the outside).

There are a bunch of NASA GTS and SCCA cars running our setup now and customers are routinely dropping 1.5-2 tenths per lap, and some recent data logging showed a customer pulling .2 MORE G just by installing our setup and dropping the front spring rate 150lbs. (less spring rate is required when you mechanically reduce the roll-tendency through roll-center adjustment).

The rear of the E36 and E46 does not change anywhere near as much as the front when lowering (due to the entirely different rear arm layout compared to the struts in front) and so huge improvements can be gained from this simple mod.

Our roll-center/bump-steer only setups are only $550 and press into a stock E46 arm, while our complete race front kits come with tubular chromoly arms and run $1050. Both include all race quality heims and spherical bearings and you're getting a setup that is used and tested by some of the best racers in the country.

Check out SLRspeed.com



https://fbcdn-sphotos-e-a.akamaihd.net/hphotos-ak-ash3/62179_568406389836075_640276508_n.jpg_nr_
 
#89 ·
Moving ball joint

I don't know if I missed this, but moving the ballpoint out of the arm won't fix roll centers. It just looks that way. The pivot point at the ball joint is actually where the roll change happens. If you draw a line through the center of the ball joint, and the pivot of the control arm that's your angle. The arm will look level, but the center didn't move at all. A modified spindle is an option. A fabricator for the VW MK5 GTI makes one. It addresses all the issues. It fixes bump steer too. With that approach you can use stock ball joints. No squeaks, or greasing. Less vibration. I don't see why it couldn't be done for our cars.
 
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