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Old 12-23-2009, 09:07 PM   #1
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This is the roll center, suspension pickup, and steering angle modification thread.

Disclaimer: Modifiying a cars suspension in the ways discussed in this thread will always result in some compromise. Increased steering angle makes things rub, raising the subframe increases anti-squat, etc. Please read through and understand the concepts before you go hacking up your car in pursuit of performance.


Part I: The Basics.

The Front Suspension:

Tension rods: These control caster, anti-dive, and anti-lift in the front suspension. Caster helps determine camber gain over the suspension stroke, and camber change throughout steering angle. Caster also helps “auto turn” the wheel when countersteering. The angle of the tension rod (horizontal plane, front to back) also helps determine anti-dive under braking situations, and anti-lift on acceleration.

Tip: If you’re using your tension rods to adjust caster more than one or two degree(s) past factory settings, there will be bind in the lower control arm's traditional rubber or urethane bushing. It’s recommended that you change to an aftermarket control arm with a heim joint/spherical bearing.

Front lower control arms: Determine your roll center, track width, and camber curve. The actual arc these move in is the camber curve (as dictated by the tension rod).

Tie rods: are used to adjust toe in the front, and obviously to steer your car. Aftermarket tie rod ends can be used to adjust bumpsteer by spacing the tie rod end parallel with the FLCA pivot points.

The Rear Suspension:

Rear upper control arms: Used to adjust static camber. The actual arc these move in is the camber curve, but keep in mind that all of the rear arms help determine this. They also help determine roll center, similar to a double wishbone setup.

Toe rods:These control static toe and toe change during suspension compression. When lowered aggressively, our cars toe and camber curves are significantly changed, becoming “steeper” (more change with less movement).

Traction rods: Determine caster (or thrust angle) on the rear suspension. As with the front, this helps determine the camber curve of the rear suspension.

Tip: On an aggressively lowered car, these should be lengthened (to about 8.5in) for a less aggressive toe curve and less bumpsteer.

Rear lower control arms: Help determine roll center, anti-squat, and can affect camber. The angle front to rear of the control arm (horizontal plane, front to back) determines anti-squat (along with the angle of the camber arm and traction arm subframe mounts). The flatter the control arm, the more squat. S13’s have a lot of anti-squat, S14 and 15’s have significantly less. The angle side to side (horizontal plane) is what helps determine roll center.

All of the suspension components are affected when lowering the car, especially when lowered to the extreme. Correctly modifying the suspension pick up points or knuckles to correct for these changes can reap large rewards, including better camber and toe curves, less body roll for a given spring rate/anti-roll bar, and more traction/grip.

Roll Center:

Front roll center is determined by the angle of the lower control arms and the angle of the upper strut mounting points. These angles, drawn in space, determine the instant centers for the front suspension (instant centers are the points that the entire suspension moves around during body roll). Then take a line from each instant center to the middle of the tire tread on the opposite side, and where these lines intersect, there is your front roll center.

Rear roll center (for our cars) is determined much like a double wishbone setup. Use the angles of the upper and lower control arms to determine the instant centers of the suspension. Then, just like the front, take a line from each instant center to the middle of the tire tread on the opposite sides. The intersection is your rear roll center.

Roll center angles must be measured from pivot point to pivot point. Modifying merely the angle of the arm doesn't do anything at all.



Center of Gravity:

The center of gravity is the point at which all the weight of the car is balanced. It’s roughly the crank centerline in the front, and above the differential in the back. You can find out your exact CG by using scales, but that is beyond the scope of this article.

Roll Couple:

Roll couple is the distance between your center of gravity and roll center. This is the reason that lowered cars have more body roll. The roll center moves lower (due to the change in angle of the suspension arms), while the center of gravity is only lowered as much as the body of the car. This makes the distance between the two longer, thus the roll couple longer, which gives the body more leverage on the suspension. I’m sure we all know how much of a difference leverage can make.

You actually want your roll center just under your center of gravity.

Part II: Roll Center Adjustment

The ways to actually adjust roll center in the front and rear are these:

1. Use a ball joint with a shank that is longer, thereby spacing the pivot point at the knuckle farther down.

The only ball joints that I’ve seen that actually have a longer shank are Sunline Racing, Moonface, and Nagisa auto:

Nagisa:



Beware of "Roll Center Adjusting ball joints" that just space the ball joint up. The ball joint shank needs to be longer. Nagisa has a good illustration (bad on the left, proper on the right):



The above method is only so effective. Due to the angle of the ball joint, using a long shank increases ackerman, and at about 20mm of correction, the lower control arm starts running into the brake rotor.

Dan at Parts Shop MAX made a nice diagram showing how the ackerman change happens:



2. Purchasing aftermarket lower control arms that have roll center adjusting heim joints and shanks.

There aren't a whole lot of arms that offer more than 10-15mm of correction because of brake rotor clearances. Ikeya Formula has some correction, and PSM has a 5mm fine adjustment spacer.



3. Modifying your stock arms. This is a little more complicated, but anyone who isn't afraid of some fabrication and taking his time can do this.

Here's the basics of what you need:

- (4) COM series QA1 3/4" spherical bearings
- (4) 3/4" spherical bearing weld in housings
- (4) Coleman Racing extra long ball joint studs with Chevy 7* taper
- (1) 7* taper drill bit from Speedway*Motorsports
- (4) pairs of 3/4 to 5/8 high misalignment spacers

And 95KA-turbos' old setup:



4. Modify the subframe pickup points (moving them farther up), thus changing the angle of the arm.

NOTE: If you plan on raising the front control arms' inner pivot point, it’s a good idea to move the steering rack up an equal amount or you will run into some big bumpsteer issues.

JIC Magic S15 front setup:



5. Modifying the pickup points on the knuckle (usually by creating a whole new knuckle), dropping them lower. Also, raising the hub location in the knuckle, which effectively creates a "drop knuckle"; a knuckle that lowers the car while keeping roll center similar. Some of the kits actually combine both ways, raising the hub, and lowering the pickup points.

Driftworks makes drop knuckles, 45mm in the front, and 50mm in the rear. The rears have urethane bushings for the control arms:



Stock knuckle:



Driftoworks knuckle:



Here they are installed, you can see the control arms are nearly flat.





Parts Shop MAX Pro knuckles with 45mm correction:





And their new forged pro knuckle:





Parts Shop MAX rear 25mm drop knuckle with spherical bushings:



Here's a comparo shot between the Driftworks and PSM:



Cor Integration's knuckle with 45mm correction:





Wisefabs front suspension kit, with a 56mm drop knuckle:



GKTech's new billet aluminum knuckles have 40mm correction:





And their rear 40mm forged aluminum drop knuckle:





And GKtechs bolt on knuckle adapter with 40mm of correction:



Track Day Performance has a billet aluminum front suspension kit with 70 or 100mm of correction.









You can also modify your knuckles yourself if you have some fabrication experience.









6. You can move the whole subframe up, correcting the suspension geometry much like the modified knuckles.


You can do this with Parts Shop MAX’s subframe risers:



Installed:



Or SPL’s subframe adjusters (which can be either set for stock, or raised for ride height correction). These also can be ordered in an offset pattern, so you can mount a S14/15 subframe in your S13:



NOTE: Raising the subframe also increases anti-squat. SPL provides a very good link on how pushing the Subframe affects anti-squat and roll center:

http://splparts.com/instructions/SPL_SSB_S13C.pdf

Some guys have taken this to the extreme:



You Z and R-chassis guys are left to either convert to McPherson strut front suspension, or modify S-chassis parts to work. Luckily your dual control arm setup isn't nearly as suseptible to roll center drop as ours:





Another geometry trick is to adjust the toe arm mount on the knuckle, helping correct the toe curve, which helps traction. (Modify the toe arm on the knuckle so that your toe rod is parallel with your LCA): You can do this with your regular cast iron uprights if you don't plan on buying drop uprights as well. GKtechs rear knuckle will have an adjustable toe arm mount for this reason.



Here's a cool Drift Tengoku article about chopping the re-welding the lower part of the knuckle, including the LCA pickup:



JIC rear setup:



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Old 12-23-2009, 09:08 PM   #2
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Part III: Steering Angle Modification

There are several ways to go about this, like tie rod spacers, steering rack spacers, and knuckles.

Classic steering angle spacer:



Big steering angle spacer:



There are a bunch of other companies that offer modified knuckles now, including:

MA-Motorsports modded:



Billspeer 555 Knuckle:



Abercrombie:



Cor Integration:



Driftworks claims 65 degress of steering lock:





Parts Shop MAX has 62 degrees of steering lock:



Wisefab also claims 65 degrees of lock:



And their ackerman adjustment spacers:



Track Day Performance claims up to 70 degrees of lock:



GKTech has a bunch of different arms available for their knuckles, they gave a pretty great breakdown:



Blue = Standard steering arm
Red = Extreme steering arm
Pink = JP Special steering arm
Green = Zero Ackerman steering arm

An overview of the different steering arms:
- Standard steering arms are exactly that, they're in the same position as the standard steering arms and are ideal for circuit/track racers or non drift cars that aren't after extreme steering angle
- Extreme steering arms feature; the fastest turninng/transitions of all 4 arms, gives the most inside wheel lock (+12 degrees over factory steering arm), has the most Ackermann effect of all the arms.
NOTE: offset steering rack extenders or steering rack relocation required (we sell offset steering rack extenders for $69 if ordered at the time you're ordering the knuckles)
- JP Special steering arms feature; similar turning speed to the standard steering arm, -4 degrees of lock (yes, slightly less steering lock from the arm itself), very linear response, even at extreme lock angles, - less Ackermann effect than standard or extreme steering arms
- Zero ackerman steering arms feature; - keeps the wheels pointing in the same direction at all steer angles (ie no Ackermann effect), similar turning speed to the extreme steering arm, +3 degrees of steering lock from inside wheel and +13 degrees of lock from outside wheel, less tendency for the tie rod on the inside wheel to overcentre, meaning no need for offset rack spacers or rack relocation, gives the most outside wheel lock (assuming it doesn’t hit the castor rod), reduces tyre scrubbing and avoids washing off speed mid-drift

Overcentering:

Another thing that's rarely mentioned when talking about all this increased angle, is the tendency of the steering rack to go "over center". This is where the angle of the tie moves farther than parallel with the knuckles steering arm. This can be alleviated a couple ways:

1. Moving the steering rack forward:






2. Spacing the tie rods farther forward, using spacers like these Driftworks ones:

Version 2:




Or the Parts Shop MAX version:



These do the same thing as the eccentric bushings, but have more correction. And there have been talks of solid steering rack bushings warping and becoming loose.

NOTE: These could put stress on your rack that it was not designed for.

3. Using Parts Shop MAX steering rack eccentric bushings:





Dan gathered some interesting information about how moving the rack forward effects ackerman angle:



Ackerman in the steering:

Now this has been a big topic of debate among the s-chassis crowd.

Here’s a good article on ackerman:

What is Ackerman Steering and how it affects handling.

Basic image of ackerman reduction:



Ackerman is built into our steering from the factory. It’s what makes the outside wheel in a drift turn at a farther angle than the inside wheel. Now when you get to extreme angles of steering lock, the effect becomes much more prevalent. This makes the inside wheel “scrub” causing the car to lose speed and reducing steering response.

Modifying the knuckles for zero ackerman makes the wheels both turn the same angle, allowing you to maintain speed at very high angles, as well as increasing the steering’s responsiveness at those angles.

But, for those of you that do roadcourse work, this will cause slightly reduced turn-in, and in tight turns the outside wheel will be scrubbing a bit, possibly causing a bit of understeer or too much heat in the tires.

Really it’s all up to the driver and how he likes it to feel.

You can also modify your tension rods and sway bar for more inside clearance. PSM LCA's already have the tension rod farther in, but Cor Integration makes a nice 25.4mm custom bent sway bar and bent tension rods that give you extra clearance.







Depending on your knuckle/LCA/tie rod end combo, you're probably going to need longer tie rods. Here's a nice list of lengths:

89-94 240sx.. 11.10" (m12x1.25)
95-98 240sx.. 11.37"
94-99 maxima 11.42"
96-99 i30...... 11.42"
97-01 Q45..... 12.00" (same with 01-06)
00-04 i30...... 12.91"
99-03 maxima 12.91"
03-08 maxima 13.30" (same with 04-06)
PSM Spherical....12.5"


Let's discuss.
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Old 12-23-2009, 09:56 PM   #3
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wow looks like you put a lot of work into getting this thread started. very informative. good job imo
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Old 12-23-2009, 10:13 PM   #4
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In for info and updates I like where this thread is going
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Old 12-23-2009, 10:21 PM   #5
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Great job and good info, thanks for taking the time to do this.
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Old 12-23-2009, 10:28 PM   #6
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Awesome info!!! Thanks!!
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Old 12-23-2009, 10:33 PM   #7
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You're welcome guys. This is something I kind of geek out on, so I thought I would contribute to the community.

Here's a question I have.

It seems like if you did all the roll center adjustment you possibly could, you could actually put the roll center above stock, even on a slammed car. Anyone know if this is detrimental to suspension performance or not? Maybe it's advantageous?
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Old 12-23-2009, 10:54 PM   #8
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There various thread on NRR already dealing with these topics
one of the more extensive ones:

Roll Center.....again - Nissan Road Racing Forums

good topic, I've seen the suspension set up of a Porsche GT3 Cup car and it floored me
just like our cars they're McPherson struts up front with a independent arms in the rear
I want that in my car
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Old 12-23-2009, 10:56 PM   #9
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i <3 this thread

i own the PSM subframe risers and knuckle/LCA kit. complimented by the rest of their GEN1 catalog lol....

i want MOAR now
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Old 12-23-2009, 11:28 PM   #10
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im really sure there is a ton of info here but im an uber noob on suspension and dont really nkow whats going on in some of these pictures. maybe a introductory thread that leads up to this one would be sweet!!
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Old 12-24-2009, 12:57 AM   #11
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Quote:
Originally Posted by ManoNegra View Post
There various thread on NRR already dealing with these topics
one of the more extensive ones:

Roll Center.....again - Nissan Road Racing Forums

good topic, I've seen the suspension set up of a Porsche GT3 Cup car and it floored me
just like our cars they're McPherson struts up front with a independent arms in the rear
I want that in my car

That's nice, but THIS IS ZILVIAAAAA!!! haha. I wanted a thread on here, and I want to update it with the latest products and such, not just "this is how you could possibly do it". Thanks for a solid link though, I might steal some of their pics to make this thread better.


Quote:
Originally Posted by roboticnissan View Post
im really sure there is a ton of info here but im an uber noob on suspension and dont really nkow whats going on in some of these pictures. maybe a introductory thread that leads up to this one would be sweet!!
Yeah, I might do that, but most of the general stuff is readily available and easy to find. This is the hardcore stuff.
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Old 12-24-2009, 01:22 AM   #12
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Quote:
Originally Posted by ManoNegra View Post
There various thread on NRR already dealing with these topics
one of the more extensive ones:

Roll Center.....again - Nissan Road Racing Forums

good topic, I've seen the suspension set up of a Porsche GT3 Cup car and it floored me
just like our cars they're McPherson struts up front with a independent arms in the rear
I want that in my car


That's my thread on NRR - lots of ideas got shot down in there, haha.

One of them was modifying the inner pick up point. You affect a lot more then just the roll center when you do it. There is more then enough room to drill a hole above the stock location and move the arm up a good inch. I was steered away from that by the guys on NRR though so I would listen to them.


Also, my rear arms are corrected more then stock, I just don't have any spacers on them yet. You can see the slight angle difference from my toe arm and LCA. I should be able to get it mostly flat, but I've got to track down the proper spacers.


Also, you don't necessarily want the roll center back to the factory location. The 240 wasn't exactly a performance monster from the factory. I haven't done enough research to say what might be optimal...so going for straight LCAs is a good goal for now. I'll be able to fine tune it as I drive it.
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Old 12-24-2009, 01:32 AM   #13
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Oh wow this thread has definitely been one ive been waiting for/ planning to make. Ive been researching this stuff forever too but it seems like you have covered a lot of it! NICE JOB!
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Old 12-24-2009, 05:45 AM   #14
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I did all the mods to 95KA-turbo's suspension. Let me tell you that this wont be an easy install. All the parts that where ordered had very close tolerences. I had to grind down/sand a few things to get it to work. We dont now how its all gonna work out because we are in the R&D mode right now. Once we get it set the way we want it we will report back here with updates. Hope fully in about 2 months when the car is rolling under its own power.

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Old 12-24-2009, 08:06 AM   #15
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Very informative! Thank you very much for putting this together.
I am interested to see how these mods are affected by the sactioning bodies. Last I read is that you could only move your pick up points 1" in any given direction.
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Old 12-24-2009, 08:30 AM   #16
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Quote:
Originally Posted by 95KA-Turbo View Post
That's my thread on NRR - lots of ideas got shot down in there, haha.

One of them was modifying the inner pick up point. You affect a lot more then just the roll center when you do it. There is more then enough room to drill a hole above the stock location and move the arm up a good inch. I was steered away from that by the guys on NRR though so I would listen to them.
nice, I keep going back to that thread for inspiration from time to time
the griggs stuff that was posted there haunts me, specially their 3 piece knuckle.





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Old 12-24-2009, 09:23 AM   #17
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I modified the stock lowers (rear and front) to acccept 3/4" spherical bearings and monoball studs for roll center adjustment. No pics of the fronts yet. But I had to ream the uprights to a 7° GM taper for the studs to work.



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Old 12-24-2009, 09:30 AM   #18
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Quote:
Originally Posted by PoorMans180SX View Post
I don't see how this would affect more than the roll center. There is no real camber curve to a McPherson front suspension other than the arc of the front control arm, and toe is controlled by the tension rods, which remain in the same place. Maybe if you had stock tension rods. I guess I'll have to look through that thread.
Tension arms control caster, unless you are talking about the tie rods.
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Old 12-24-2009, 09:44 AM   #19
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Quote:
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Tension arms control caster, unless you are talking about the tie rods.
I am sure it was a simple slip up in typing, but yes that's important to point out, haha.

I personally do not 100% understand how moving the inner point up effects the motion of the tension rod - I mean it should technically do the same thing as lowering the outside out point. I was assured that it would put some unforeseen forces on the arm that would screw up everything. I am not an engineer - perhaps Def will come in and explain. It is stated in that NRR thread. I got mad because no one would explain it to me at first, then I got a kind of half-ass explanation from a few people.
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Old 12-24-2009, 09:46 AM   #20
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Tension arms control caster, unless you are talking about the tie rods.
That is correct.

And therein lies the problem, if you move the FLCA pickup points up, because the rack would also need to go up along with the FLCA pickup points so that the tie rods' arc and the FLCAs' arc will stay in sync.

If not, the car will get some nasty bumpsteer. that pretty much cannot be corrected due to the 2 having totally different arcs.

Edit - if you move the FLCAs' pickup point, then the T/C rods' pickup points will have to move up the same amount as well.

Think about it.

If you moved the FLCAs' pickup points by an inch, and if you flattened it, the T/C rods will no longer be parallel to the FLCAs anymore. They'd be pointing up in order to meet the FLCAs, and probably no way for them to bolt up to the FLCAs because of the angle that they're in, so they will need to be moved up an inch as well.
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Old 12-24-2009, 10:01 AM   #21
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If not, the car will get some nasty bumpsteer. that pretty much cannot be corrected due to the 2 having totally different arcs.
Well corrected to a point with a bumpsteer kit but they can only correct so much before moving the whole rack up is the next option. Which in my case with the LSx is a no go, there is about 1/16" between the rack and the oilpan.
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Old 12-24-2009, 10:11 AM   #22
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Originally Posted by SoSideways View Post
If you moved the FLCAs' pickup points by an inch, and if you flattened it, the T/C rods will no longer be parallel to the FLCAs anymore. They'd be pointing up in order to meet the FLCAs, and probably no way for them to bolt up to the FLCAs because of the angle that they're in, so they will need to be moved up an inch as well.
Exactly, I liked the solution on the Porsche cup car
the traction rod connects to a perpendicular brackets and it's position can be adjusted with round spacers of various lengths held with a bolt
the lower control arm is a two piece design cast in aluminum - shims can be stacked near the crossmember bushing held by two bolts to adjust track and probably quick alignment changes.
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Old 12-24-2009, 10:12 AM   #23
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Ah that's right, it makes sense to me again. I had forgotten how I had to think of it to make sense, haha.

By moving the inner point up, you are making the LCA angle better but the tension rod angle worse. By moving the outer point down you are making your tension rod angle and LCA angle better at the same time. The tie rod angle can be fixed with spacers and heim joints, much like the spherical bearings and spacers used for the roll center.


Here is an interesting article that somewhat explains why one type of roll center isn't ideal for everyone/every car. Unfortunately they're talking about stock cars and they have completely different suspension set ups then we do:

Accelerating Performance: Roll Center Magic
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Old 12-24-2009, 10:14 AM   #24
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The point is, the tie rods' pick up point will differ from the FLCAs' pick up point if you move just the FLCAs. One will be higher than the other, which will cause different arcs.

When 2 arms have the same arc, you can correct for stuff much easier.

When you have 2 arms that have different arcs now, it is much harder to correct for that type of stuff....
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Old 12-24-2009, 10:43 AM   #25
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Loving this thread, and the work that went into making it. True, this is more of a NRR-type thread (that site is awesome, btw, I just got turned on to it recently), but I love that the community is moving towards real performance modification, not just 'this looks cool', or 'check out what i did for free'.

Makes me proud

Luke (Blu808) and I have been talking over making some CNC aluminium LCA's since we both have access to CNC machines and I have all the heim joints. We just need to come up with a final design (which has to address roll center, bump steer if possible, big angle kits, etc) ~ maybe this thread will help.
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Old 12-24-2009, 11:33 AM   #26
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Originally Posted by GSXRJJordan View Post
Loving this thread, and the work that went into making it. True, this is more of a NRR-type thread (that site is awesome, btw, I just got turned on to it recently), but I love that the community is moving towards real performance modification, not just 'this looks cool', or 'check out what i did for free'.

Makes me proud

Luke (Blu808) and I have been talking over making some CNC aluminium LCA's since we both have access to CNC machines and I have all the heim joints. We just need to come up with a final design (which has to address roll center, bump steer if possible, big angle kits, etc) ~ maybe this thread will help.
agree, I'm interested in what you and Luke will come up with
we're in a similar situation, we can make just about anything but it's not very useful without a well thought out design
any automotive/mechanical engineers in socal that are serious about making cool shit, get at me
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Old 12-24-2009, 11:42 AM   #27
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That's my thread on NRR - lots of ideas got shot down in there, haha.

One of them was modifying the inner pick up point. You affect a lot more then just the roll center when you do it. There is more then enough room to drill a hole above the stock location and move the arm up a good inch. I was steered away from that by the guys on NRR though so I would listen to them.


Also, my rear arms are corrected more then stock, I just don't have any spacers on them yet. You can see the slight angle difference from my toe arm and LCA. I should be able to get it mostly flat, but I've got to track down the proper spacers.


Also, you don't necessarily want the roll center back to the factory location. The 240 wasn't exactly a performance monster from the factory. I haven't done enough research to say what might be optimal...so going for straight LCAs is a good goal for now. I'll be able to fine tune it as I drive it.
I liked this idea:


It's what silk road does on their time attack car. I wish I had more data on it but have only seen one article.
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Old 12-24-2009, 11:42 AM   #28
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wow, nice thread, you saved myself the embarrassment of making a n00b ver. of this thread. lol.


this is complicated. but it shows the importance of all the arms
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Old 12-24-2009, 12:39 PM   #29
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Quote:
Originally Posted by GSXRJJordan View Post
Loving this thread, and the work that went into making it. True, this is more of a NRR-type thread (that site is awesome, btw, I just got turned on to it recently), but I love that the community is moving towards real performance modification, not just 'this looks cool', or 'check out what i did for free'.

Makes me proud

Luke (Blu808) and I have been talking over making some CNC aluminium LCA's since we both have access to CNC machines and I have all the heim joints. We just need to come up with a final design (which has to address roll center, bump steer if possible, big angle kits, etc) ~ maybe this thread will help.
In respect to rear roll center adjustment, would you guys be making a set of rear spindles with the option of using spherical inserts and a z32 for type mount for the struts? I'd like to be able to use my z32 rear e-brake assembly as well.

To add to this thread, adding additional roll center adjustment for the rear (ie lower control arm) could possible hurt the rear geometry of the other arms. The best fix would be to replace the rear spindle to ensure that the arc movements remain unaltered.
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Old 12-24-2009, 12:54 PM   #30
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Definitely, a new spindle out all around is by far the best method to correct everything properly. An adjustable control arm on top of that would be great, then EVERYTHING could be adjusted.
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