This is the roll center, suspension pickup, and steering angle modification thread.

[PoorMans180SX]

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 steering axis inclination. Caster also helps “auto turn” the wheel when countersteering. The angle of the tension rod (vertical 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 arms traditional rubber or urethane bushing. It’s recommended that you change to an aftermarket control arm with a heim joint.

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.

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 curve is 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 (vertical plane) determines anti-squat (along with the angle of the camber arm and traction arm mounting points). 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 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 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. Most of the "RCA" ball joints don't do anything besides move your arms closer to the ground.



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 your roll center. This is the reason that lowered cars roll more. The roll center moves lower (due to the angling down of the suspension arms), while the center of gravity only gets 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. This means on an extremely lowered car, it might not take as much adjustment as you think, as you don’t want to put your roll center above 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/pillow ball 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:

Sunline:



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):





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

There are many different brands; Ikeya Formula and Parts Shop MAX being the only brands I know of that aren’t just the same arm painted different colors. Megan Racing makes Ikeya knock-offs, and Godspeed/Battle Version/Driftworks/Circuit sports all use the same type of arm.

Ikeya formula:






Driftworks:




Parts Shop MAX are in development and should be out by the new year:







3. Modify 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 -*www.pitstopusa.com - Detail*--- this may be a better product though -*www.pitstopusa.com - Detail
- (4) 3/4" spherical bearing weld in housings -*www.pitstopusa.com - Detail
- (4) Coleman Racing extra long ball joint studs with*Chevy*7* taper -*Racing and Car Products - Coleman Racing - Stud, Mono-Ball, Extra Long
- (1) 7* taper drill bit from Speedway*Motorsports*-*Tapered Ball Joint Reamers - 7 Degree
- (4) pairs of 3/4 to 5/8 high misalignment spacers -*High Misalignment Spacer - 3/4" to 5/8" (pair) Barnes4WD.com - Off Road Fabrication Parts

And 95KA-turbos's setup:




I know it sounds very complicated, but it will make sense if you actually put it all together.


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:



For the rear, you can actually move the rear LCA pickup points to adjust squat and roll center at the same time (which especially helps on S13’s and Z32’s, which have a lot of anti-squat stock). To adjust squat, you have to change the angle of the lower control arm front to rear, aka moving the back pickup point up.

Stock (S13):



Here is the Parts Shop MAX S13 Silvia in Japan, which has decreased anti-squat and slightly raised roll center:





The driver of this car reports that he has better rear traction, especially while sideways and braking.

The S14 and S15 have more squat dialed in from the factory, but things can still be adjusted in the same way.

5. Modifying the pickup points on the knuckle (usually by creating a whole new knuckle), dropping them lower.

SP-tec (and Driftworks's version of SP-tec) are a couple of companies that make custom front and rear knuckles, which have urethane bushings instead of stock rubber:


Driftworks:



Parts Shop MAX (yet to be released) with spherical bushings:



PSM front knuckle (available now, anywhere from zero to 40mm correction, you specify when ordering):





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

Another 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.



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:

[PoorMans180SX]

Part III: Steering Angle Modification

Modifying the steering angle is obviously most useful in drifting, but it can help in a roadcourse situation, as it makes your steering rack quicker (2.5 turns lock-to-lock instead of 3)

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

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

Parts Shop MAX modified knuckles (no roll center correction on these):



Notched lower control arms



One good thing about the PSM parts is the way they modify the knuckles, the knuckle mod hits the LCA and not the tie rod end.

PSM knuckle:



MA-motorsports modded:



GP Sports knuckles, which are cast and correct for roll center a little. NOTE: They no longer make their "Hyper Knuckle" kit with roll center spacers and lots of angle gain for the S-chassis. The knuckles pictured only give you 10 degrees of increased steering angle, and 10mm roll center correction.



KPR knuckles:



Billspeer Ultra Knuckle:



And the Driftworks:



95-KA turbo has an interesting setup, where he notched his lower control arms so the tie rod end has full contact with the control arm. I think he was trying to lessen damage to the tie rod end.



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:






They need to be modified for LHD though, like this:



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.


Now some of the parts I mentioned in RCA help with steering angle (such as the driftworks knuckles), or would need to be modified if you are going to use them and want more steering 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.


Let's discuss.

[sincity_sil80]

wow looks like you put a lot of work into getting this thread started. very informative. good job imo

[hotlavaflow]

In for info and updates I like where this thread is going

[Shadowhunter]

Great job and good info, thanks for taking the time to do this.

[Teknolust72]

Awesome info!!! Thanks!!

[PoorMans180SX]

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?

[ManoNegra]

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

[theslows13]

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

[roboticnissan]

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!!

[PoorMans180SX]

Originally Posted by ManoNegra

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.

Originally Posted by roboticnissan

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.

[95KA-Turbo]

Originally Posted by ManoNegra

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.

[om3ga]

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!

[ballinnmiami240sx]

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.

Danny

[Jonnie Fraz]

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.

[ManoNegra]

Originally Posted by 95KA-Turbo

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.

[Otto347]

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.

[Otto347]

Originally Posted by PoorMans180SX

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.

[95KA-Turbo]

Originally Posted by Otto347

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.

[SoSideways]

Originally Posted by Otto347

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.

[Otto347]

Originally Posted by SoSideways

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.

[ManoNegra]

Originally Posted by SoSideways

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.

[95KA-Turbo]

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

[SoSideways]

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....

[GSXRJJordan]

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.

[ManoNegra]

Originally Posted by GSXRJJordan

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

[S14DB]

Originally Posted by 95KA-Turbo

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.

[udon!]

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

[mmdb]

Originally Posted by GSXRJJordan

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.

[95KA-Turbo]

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.