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

[Patrick Bowering]

I seam to remember something bout the pbm guys running very low caster numbers and having good luck with it but that wobble is fucking horrible. dan do you have any bits to add? also could have "georges" big rack spacer on both sides be causing any problems. I just could not come up with any other way to lengthen my tie rods.

[articdragon192]

Dan, I'm curious... I know my Z32 has aluminum knuckles, and making any kind of knuckle mods is either a big risk, or just nonexistent. If I swap over to R32 GTS knuckles, I know I'll have better luck witth mods. Now my question is, can the roll center correction and addition of angle come close to that of an s-chassis if I do end up swapping to R32 knuckles and getting those modded by you?

[mikerbike]

Originally Posted by JaredP

Just remember when you lengthen the tension rod its not the same as moving the tie rod forward. Moving the tie rod alone moves it independently of the ball joint.

Yes. I already explained that.

Originally Posted by JaredP

All you did was effectively mess with caster and cause your wobble

False. I also gained drift trailing wheel angle. I explained that too. That's one of the reasons I lengthened the tension rod.

Originally Posted by SoSideways

Yeah you're not moving the inner pivot, you're just moving the angle of the tie rods.

Correct. But I'm moving the outer tie rod and ball joint forward, changing the relationship between the inner tie rod and the lower ball joint/outer tie rod the same way as moving the rack forward would. See what I'm getting at?

Originally Posted by SoSideways

What you're doing that is making it so you don't over center, but at the expense of really low caster, which is not good.

False. I'm making it overcenter worse, not getting rid of the overcentering. As the LCA swings back, the drift leading wheel doesn't get much more angle because it's stopped by the LCA bumper thingy. But I can look straight down the length of the tie rod and see that the lower ball joint is really close to the line that intersects the two tie rod pivots. As the LCA swings back forward, the lower ball joint gets further from the tie rod line.

Originally Posted by Patrick Bowering

I seam to remember something bout the pbm guys running very low caster numbers and having good luck with it but that wobble is fucking horrible. dan do you have any bits to add? also could have "georges" big rack spacer on both sides be causing any problems. I just could not come up with any other way to lengthen my tie rods.

This is the second reason I was lengthening the tension rods. Less caster, for flatter contact patch for the drift leading wheel at full lock (any amount of lock I guess.) There was a few pages in this thread where people were talking about it, so I wanted to try. I STRONGLY feel like the lower caster angle isn't my problem.

[JaredP]

Maybe its just me but can you link me to anything explaining how lower caster numbers will provide a larger contact patch as you steer the wheels. I'm just not seeing it

[KA240SX808]

Less caster = Less camber lean.

[TheRealSy90]

Cool little video. It is an FC chassis though.

Real angle at 0:36

George Marstanovic Vegas Pro Am Round 3 - Ksport GT Pro Suspension - YouTube!

[JaredP]

Originally Posted by Nismo240R

Less caster = Less camber lean.

Gotcha, was trying to wrap my head around it

[Future_gohan]

Originally Posted by articdragon192

Dan, I'm curious... I know my Z32 has aluminum knuckles, and making any kind of knuckle mods is either a big risk, or just nonexistent. If I swap over to R32 GTS knuckles, I know I'll have better luck witth mods. Now my question is, can the roll center correction and addition of angle come close to that of an s-chassis if I do end up swapping to R32 knuckles and getting those modded by you?

I'm curious to this answer aswell, as i'm trying to get a setup with your knuckles, coilovers, and lca/tension arm setup on the front.

[GripTerror]

would make my life happy too if z32 knuckles can be modified in the rear

[SoSideways]

Originally Posted by mikerbike

Correct. But I'm moving the outer tie rod and ball joint forward, changing the relationship between the inner tie rod and the lower ball joint/outer tie rod the same way as moving the rack forward would. See what I'm getting at?

How are you doing this? You cut and weld the LCA so the ball joint is further forward than the inner pickup piont?

Did you also bend the tie rods or something so the tie rod end is now further forward as well?

False. I'm making it overcenter worse, not getting rid of the overcentering. As the LCA swings back, the drift leading wheel doesn't get much more angle because it's stopped by the LCA bumper thingy. But I can look straight down the length of the tie rod and see that the lower ball joint is really close to the line that intersects the two tie rod pivots. As the LCA swings back forward, the lower ball joint gets further from the tie rod line.

I have no idea that the LCA swings back and forth as you turn the wheel? It may move very slightly, but it doesn't "swing back and forth".

This is the problem I have with your posts. I can't understand what you're saying. I can't understand the stuff you're describing. Everytime I read your posts I get confused.

I am not being an ass, I'm trying to help you figure out why your car is acting funny, but I cannot, for the life of me, understand what you're trying to say.

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When you lengthen the tension rod to reduce positive caster, most of the time with stock type LCAs, the LCA inner pivot starts to bind up. Without touching anything else on the front suspension, if you reduce the positive caster down to like 4 or 5 degrees and fixing the toe setting so you're at zero toe, you will reduce the max angle you will get, but by doing so, you also reduce the chance of over centering, as now the tie rod ends will make contact with the steering stoppers sooner than before. This is both because you have to shorten the total length of the tie rod assemblies and the angle between the LCA and tie rods relative to their inner suspension pickup points.

On the flip side of the coin, if you add positive caster (by shortening the tension rods) and not touch anything else in your suspension other than to fix your toe so you're at zero toe, you should gain maximum angle at full lock, at the expense of running into over centering problems. This is because of the longer tie rod assemblies and the angle between the LCA and tie rods relative to their inner pickup points.

Trust me on this, I've had the car up on jack stands most of last year, and I spent at least 2 hours on it almost every night in the garage playing with all the different setups and experienced them first hand and saw them with my own eyes, then my findings were confirmed on here by people that did the same thing as I did. Even PBM Dan's findings back up what I have found on my own.

[mikerbike]

When I lengthen the tension rod, the LCA moves backward. When i shorten the tension rod, the LCA moves forward. Simple. I didn't say the outer ball joint moves fore and aft as I turn the wheel. I said it moves fore and aft as I lengthen and shorten the tension rod.

Are you still confused?

[SoSideways]

Nope, you actually made that pretty clear.

It's just when you start saying stuff like "it swings forward" or "it swings back", it tends to sound like things are moving in a dynamic kind of way, which, if your LCAs were indeed swinging back and forth, then you need to fix your tension rods because they be broke at that point.

[mikerbike]

Dang. Now I see. Sorry.

Anyway, with the rack at full lock to the right, working with the right wheel, as the tension rod gets longer, and the lower ball joint is moving backward in the wheel well, the right wheel gains as much drift leading wheel angle as the LCA does, becsuse the outer tie rod is stopped against the LCA stopper.

Now I need to go jack up my car again. Now I'm just talking from memory. I'll be back tonight hopefully to tell you that you're right.

[PoorMans180SX]

Okay guys. Let's hammer this down.

Overcentering is pretty much relative to your knuckles, caster (and how it's adjusted), bump stops, and rack travel. There are a few too many combinations to make generalities like "moving the control arm fore/aft reduces/increases overcentering" You know what I"m saying?

Originally Posted by mikerbike

I feel that decreasing ackerman with the offset rack spacers or moving the rack forward will solve my problem also. Here's why...

Now, at full lock, the drift leading wheel is visually close to overcentering. But it wouldn't be if the inner tie rod was an inch further forward (rack relocation or offset rack spacers.)

In your opinion, am I still on the wrong track?

To reply to this post, No, I think you're thinking about it right, and what you're saying is true, but let me answer with a question. Are you looking for a nice drift setup? Because the ackerman in those knuckles is what is going to hold you back the most. Yes, moving the rack or using offset spacers will help your current problems, but you will have more angle and less overcentering to start with if you modify the knuckles to have less ackerman and more angle. See what I'm saying? That's why I said I would start with making a new set of knuckles.

And just for the record, you aren't decreasing ackerman with the offset rack spacers. You're actually increasing it. I will give you this quote from an auto engineering article as proof:

A big factor in what dynamic toe curve is achieved is the included angle between the steering arm and the track rod (Figure 7). As this angle becomes more acute, dynamic toe out increases. To achieve this, you move the steering rack rearward in the car. This applies for steering rack forward of the axle C/L, and rearward of the axle C/L.

[Matej]

Instead of using rack spacers, has anyone attempted shortening the rack housing?

[mikerbike]

Originally Posted by PoorMans180SX

To reply to this post, No, I think you're thinking about it right, and what you're saying is true, but let me answer with a question. Are you looking for a nice drift setup? Because the ackerman in those knuckles is what is going to hold you back the most. Yes, moving the rack or using offset spacers will help your current problems, but you will have more angle and less overcentering to start with if you modify the knuckles to have less ackerman and more angle. See what I'm saying? That's why I said I would start with making a new set of knuckles.

And just for the record, you aren't decreasing ackerman with the offset rack spacers. You're actually increasing it. I will give you this quote from an auto engineering article as proof:

But, if I move the lower ball joint/outer tie rod forward the same distance as the inner ball joint, I'm not changing ackerman at all? I have one more pair of knuckles to chop up. It might be a while. Back to lurk status.

[SoSideways]

Originally Posted by PoorMans180SX

Overcentering is pretty much relative to your knuckles, caster (and how it's adjusted), bump stops, and rack travel. There are a few too many combinations to make generalities like "moving the control arm fore/aft reduces/increases overcentering" You know what I"m saying?

Go back and re-read my post.

I said "if you didn't touch anything else", implying everything else being stock, with the exception of an adjustable tension rod.

I even made mention of stock type LCA.

I know there are lots of combos out there that would change things, because as always, changing one thing changes everything in our suspensions. Which is why I made sure I put it out there that my observations were done on stock configurations with the exception of the adjustable tension rods.

[Matej]

Has it been established how large of a tie rod spacer can be used before over-centering occurs? This would be assuming everything else is stock.
The common size seems to be 5-6mm. MAX is 7mm. I have also found 4mm and 8mm. One could stack them to 9mm, 10mm, etc... Albeit at the expense of tie rod thread.

I have finally decided to just purchase tie rods such as the Tein ones that allow for usage of whatever size spacer desired.
For now the only mods I have are S14 FLCA and lots of negative camber. What is the largest spacer I could get away with?

Cheers, and I apologize for all the newbie questions.

[SoSideways]

I had stock S13 LCAs and Tein S-chassis tie rods and the PBM spacers and over centered. Pretty sure using just the stock Tein spacers would have got me over centered as well.

With the S14 LCAs, if they are indeed 10mm longer than S13 ones, then the Tein or PBM ones may work without over centering.

[!Zar!]

Caster has a lot to do with over-centering when talking about Tein inners combined with steering angle spacers rings.

[Matej]

Thank you for the information. The S14 FLCA are 15mm longer if I recall correctly, although I may be misinformed.
Speaking of FLCA, does anyone on here offer services such as extending or boxing-in the arms?
I do not know anyone in person whom I would trust to do it.

[PoorMans180SX]

Originally Posted by Matej

Thank you for the information. The S14 FLCA are 15mm longer if I recall correctly, although I may be misinformed.
Speaking of FLCA, does anyone on here offer services such as extending or boxing in the arms?
I do not know anyone in person whom I would trust to do it.

I can easily box in your arms. I am working on getting some pre-made extension sections made up so I can just cut and weld. The only thing I don't have are dimple dies, so it won't look as cool as some company's.

My knuckle jig is almost back from machining too. Let me look at my parts costs and I'll shoot you a PM.

[Matej]

That sounds pretty cool.
I found this place that sells pre-cut dimple died plates for the arms:
Products

Once you get the extension sections made I will definitely want mine done.

[DC Dan MAX USA]

Originally Posted by Patrick Bowering

I seam to remember something bout the pbm guys running very low caster numbers and having good luck with it but that wobble is fucking horrible. dan do you have any bits to add? also could have "georges" big rack spacer on both sides be causing any problems. I just could not come up with any other way to lengthen my tie rods.

A better way to lower the caster is with the MAX PRO coilover caster adjustable top plate.
You could just buy a longer tie rod like Ikeya formula.

Originally Posted by articdragon192

Dan, I'm curious... I know my Z32 has aluminum knuckles, and making any kind of knuckle mods is either a big risk, or just nonexistent. If I swap over to R32 GTS knuckles, I know I'll have better luck witth mods. Now my question is, can the roll center correction and addition of angle come close to that of an s-chassis if I do end up swapping to R32 knuckles and getting those modded by you?

we have not done the r chassis roll center yet but its not a problem to get the same results as the s chassis.
take a look at our R chassis knuckle mods so far

Originally Posted by PoorMans180SX

There are a few too many combinations to make generalities like "moving the control arm fore/aft reduces/increases overcentering" You know what I"m saying?

And just for the record, you aren't decreasing ackerman with the offset rack spacers. You're actually increasing it. I will give you this quote from an auto engineering article as proof:

I think its safe to say that if you shorten the tension rod you will pull the knuckle forward, making the outer tie rod move forward and therefore making the tie rod center with the knuckle's steering arm sooner.... and you can cancel the problem by adjusting caster on the top plate or moving the inner tie rod forward.

My latest testing shows that the ackerman is progressive with the rack in the stock position and the ackerman is digressive with eccentric rack forward bushings.
I'll make a graph when I have time, its pretty mind blowing how much difference it makes.

Originally Posted by Matej

Has it been established how large of a tie rod spacer can be used before over-centering occurs? MAX is 7mm.

you can overcenter with just our 7mm spacers and a stock knuckle

Originally Posted by !Zar!

Caster has a lot to do with over-centering when talking about Tein inners combined with steering angle spacers rings.

agreed that more caster adjusted at tension rod only makes overcetnering worse

Originally Posted by Matej

The S14 FLCA are 15mm longer if I recall correctly,
Speaking of FLCA, does anyone on here offer services such as extending or boxing-in the arms?

10mm
We do the reinforcement for $100+return shipping per pair including labor and CNC bracing.
Since you can get NEW OEM spec FLCAs on ebay for $30 ea, it is not worth it to mod a stock one for length.

[mikerbike]

On S14 control arms, are the tension rod bolt holes the same distance from the inner pivot? Meaning, the wheel is further away from the tension rod?

[PoorMans180SX]

Originally Posted by mikerbike

On S14 control arms, are the tension rod bolt holes the same distance from the inner pivot? Meaning, the wheel is further away from the tension rod?

It would be a matter of like 5mm if anything. Not enough to matter.

[DC Dan MAX USA]

Originally Posted by mikerbike

the wheel is further away from the tension rod?

thats correct

[NoPistons!]

Well, i threw diy out the window. Know what i'm getting when my taxes come back. =D


So instead of welding the godspeed style adjustable lca's crossmember adjustable mount, couldn't i just put a stronger, longer heim in and use a shitload of loctite? Think that'd be ok?

[articdragon192]

Originally Posted by DC Dan MAX USA

we have not done the r chassis roll center yet but its not a problem to get the same results as the s chassis.
take a look at our R chassis knuckle mods so far

Whoa, the link connecting the knuckle to the FUCA is definitely loads better than the Z32 one. A lot slimmer for better wheel/tire clearances. Guess I gotta find me one of those too to make the R32 knuckle swap and mod worth it.

[DC Dan MAX USA]

nopistons, The pic you posted from knoops blog, his taper rod is too long. I emailed him to let him know.

I dont want anyone to copy that LCA and get bad results, possibly blame the knuckle. The taper rod length needs to be stock to make sure there is no added bumpsteer and massive ackerman increase like the one in the pic above. Our pro knuckle mod had plenty of roll center, and if you F with that rod length you will screw up the settings we designed into the knuckle.

Our PRO FLCA(w/tension combo) taper rod does have a 5mm adjustment spacer for fine tuning but beyond that, the length should not be messed with.

Heres pix of the MAX PRO knuckle mod with OEM LCA mod.

This setup costs $500 + return shipping. ($100 to mod the LCA $400 for the knuckle)