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

[SoSideways]

He's like the project leader for the company that he works with, and I don't know how tight the security is for his company, so I would say to get in trouble over for not being to wait 3 more hours to check this forum and make a post would be kinda silly.

[240sxaddict]

So what is the optimal angle for the FLCA?

[SoSideways]

^ Depends on your ride height and strut angle as well.

[240sxaddict]

Assume the chassis mounting point is infinitely adjustable, whats the optimal angle compared to the strut?

And where can I find these

Can't find them on the PBM site.

[SoSideways]

You need to figure out the CG of the car right, then you can figure out about where you would want your roll center to be, and thus, arriving at a conclusion as to about where you would want to place your FLCAs.

There isn't a "for this much lowering, the FLCAs must be at ____ angle" rule.

It's all relative.

Look up how to find your CG and roll center and stuff, there are plenty of racing suspension related websites that go into detail how you can calculate for that kind of stuff.

[mmdb]

Originally Posted by 240sxaddict

Assume the chassis mounting point is infinitely adjustable, whats the optimal angle compared to the strut?

And where can I find these

Can't find them on the PBM site.

This only one of many ways you'll know.

[PoorMans180SX]

Will someone please clear the foam stuff out? Interesting subject, someone should start another thread on it (only with pics, those kids of threads fail without pics).

Thanks.

It's too bad PSM can't hurry up! I want to see what their drop knuckle is going to look like!

[swiftmini]

H

Originally Posted by swiftmini

I have just read through this thread. Must say its all very interesting stuff.

I have been into the whole slamming an s-body, mega steering lock, decent handling for about a year now and iam really starting to get to grips with it, defo still learning though.

In terms of lowness, iam almost on the limit for a uk car. We have speed bumps over here that are sometimes over 100mm tall and also our roads are layed by under payed, half blind council workers (damn you peeps with sat nav tarmac laying equipment). Still not that low compared to you guys in us/jp/aus.

At the moment my basic spec is: on a s13 chassis

Rear
Godspeed arms all round
Godspeed arb
Apex gen1 coilover with 8kg spring
S14 subframe
Homemade risers bushes (offset hole for s14 subframe fitment) (rigid mounted flat too body)
Cusco two way diff solid mounted

Front
Godspeed tension rods
Stock lower control arm (I had to ditch the gashspeed lower arm because the rose joints and pillow ball were stuffed after on 2000 miles :wack
Home made psm knuckle mod (psm wanted too sell me full kit when I only wanted the weld on u shape parts)
Ikeya formula tie rods
Steering rack moved forward by 18mm, soon to be 24mm. ( I have many pics to show the crossmember fabrication)(its really simple and is legit).

When I made the psm styke knuckle mod I welded the part on, tracked up the toe by eye, and tested the lock either way. I then heated up the steering arms that they were welded to and bent them outwards to remove more ackerman.

When side ways my car feels amazing but its crap on the road and over bumps.

I think that because I have lowered the tie rod end by 50mm (2inch) that I also need 50mm of rollcentre correction on the outboard lower arm ball joint, to get the curves between the two back to normal.

If I put a trolley jack under my hub and jack it upwards from full droop to full bump, you can easily see that the hub bumpsteering a lot.

I'll come back and write more stuff later

In my head I have just come up with this theory on what's happening..

The track rod is parallel to the ground which means it will effectively get slightly shorter through out bump and droop.

The lower control arm is pointing upwards towards the hub. This means it will effectively get shorter during bump and longer during droop. During bump the effective shortening of the arm will narrow the track width of the hubs but because the steering doesn't change length at the same rate it steers the wheel towards toe in.

Dunno if that makes sense?? But basically instead of reducing bump steer I think that the psm knuckles increase it dramitically.

Kev

[GripTerror]

Originally Posted by SoSideways

He's like the project leader for the company that he works with, and I don't know how tight the security is for his company, so I would say to get in trouble over for not being to wait 3 more hours to check this forum and make a post would be kinda silly.

he didnt post yet ey

[racepar1]

Originally Posted by 240sxaddict

So what is the optimal angle for the FLCA?

There is no such thing... "Optimal" is a relative term.

[longfellow]

YouTube - Tomei / Cusco WRX STi Time Attack Car
Goes over some of the suspension mods for the Cusco STI including the custom uprights.

[racepar1]

Originally Posted by swiftmini

H

In my head I have just come up with this theory on what's happening..

The track rod is parallel to the ground which means it will effectively get slightly shorter through out bump and droop.

The lower control arm is pointing upwards towards the hub. This means it will effectively get shorter during bump and longer during droop. During bump the effective shortening of the arm will narrow the track width of the hubs but because the steering doesn't change length at the same rate it steers the wheel towards toe in.

Dunno if that makes sense?? But basically instead of reducing bump steer I think that the psm knuckles increase it dramitically.

Kev

You are talking about the front suspension right? It's really pretty simple, if you move one arm without moving the other you may/may not be fixing anything. You want the arcs of used travel of the LCA and the tie rod to match as close as possible. With the right amount of spacing on the tie rod only you MAY be able to help your bumpsteer. With the wrong amount of spacing you are only going to make it worse.

I personally ran kazama tie rod ends on my car for about a week. Just from driving on the street I thought that I could feel moree bumpsteer. The car darted around more when you would hit bumps with one side of the car only. After that experience I decided that I wasn't going to mess with the steering geometry untill I was going to mess with the roll center as well. Once my setup is all done I am going to set the tie rod end spacing using a bump steer guage.

[SoSideways]

Originally Posted by GripTerror

he didnt post yet ey

I told him to check this thread and make a post about the foam situation, and all he said was for me to direct you guys over to the thread he made on Fresh Alloy about it.

Just do a search for chassis foam on google and that should be like one of the first links to show up.

He went through the whole thing pretty thoroughly, so if you still have questions after that, I'll try to relay the message to him and see if he'll make a post or at least reply to your questions.

Looks like he's been pretty busy lately, so that would explain why he's not been on here.

[PoorMans180SX]

Originally Posted by longfellow

YouTube - Tomei / Cusco WRX STi Time Attack Car
Goes over some of the suspension mods for the Cusco STI including the custom uprights.

Wow, that's some amazing work. Looks like the front uprights are steel, and the rears are aluminum. Pretty crazy design. I'm not very familiar with the Sti's rear suspension setup, so I don't really know what's going on there, but I can definitely appreciate that.

The front upright looks like it has a pretty big drop.

[longfellow]

IIRC STi's run a multi-link set up not too much different than 240's

[PoorMans180SX]

BTW, I ran SPL tie rods ends on my first car and they are magical. Definitely improved my bump steer. Just spaced them down to be parallel with the LCA.

[GripTerror]

^I did the same but lowering the car makes it garbage... after i corner balanced the car the guy that did the work made me raise it... car felt so much better.... but i think it had slightly less grip in some respects i dunno.... but easier to drive...

[PoorMans180SX]

My car was slammed on Tein Super Drifts. Soooo, you did something wrong.

[SoSideways]

Originally Posted by PoorMans180SX

My car was slammed on Tein Super Drifts. Soooo, you did something wrong.

It was probably not adjusted to create the same arc for both the FLCAs and tie rods, thus bump steer still occured.

I've noticed that with stock FLCAs and stock tie rod ends, the car does have a little bit of bump steer, but it's not that bad at all, and my car is slammed on Stance GR+.

[GripTerror]

i have spl tie rods and the flcas and tie rods were parallel.

That being said, the car felt bumpier, shittier, rolled more, was more out of control. it was all quite pronounced and noticable. Raising it back up, car felt more controllable, more compliant, significantly less roll, etc... That's why I want the geometry all corrected properly while get the benefit of being lower (from a functional not look perspective). I don't drift, I track for lap seconds around a road course.

[240sxaddict]

Originally Posted by mmdb

This only one of many ways you'll know.

I own "tune to win" and "engineer to win" by carroll smith, I understand what roll center is, just asking if anyone had figured out a roundabout sweet spot for the FLCA on a s-chassis.

[mmdb]

oh thought you were one of those guys who were just like "tell me the BEST EVAR SETUP!" type of poster. Sorry! hehe.

Anyway. I've played with roll center a bit and after adjusting it here and there my chassis was at it's happy spot with ~30mm of height in the front and 15mm in the rear. When I had it at about 50mm of adjustment I would get sudden understeer through corners, which could be due to the shocks bottoming out, or just too much roll center adjustment vs the rear, or in other words the front being too high vs the rear.



You can tell in the picture that the pivot points of the LCA is pointing up, significantly increasing roll center height.. This was with ~50+ mm roll center correction. I'm sure the car would've handled mo-betta if I had more adjustment in the rear, as the rear arms were still angled down, rather than up.

So going back to your question, it is highly unlikely that you'll find a solid answer; all things (sway bars, suspension settings, springs, wheels) affect roll center among other things.

[240sxaddict]

To be fair my question was vague and sounded very lazy. Sorry!

[WISH ONE]

Originally Posted by 240sxaddict

I own "tune to win"

I have "tune to win" as well its a must have for anyone trying to understand all of this. Super old school, but it has all the fundamentals.

[white92_s13]

HEY!

So a few pages back i posted pictures of my modified my ae86 knuckles and boxed lower control arms. anyways UPDATE! i have installed these.

Boxed lower arms
shortened knuckles
megan tie rods
battle version nrca
energy bushings
trd 8k 6k springs
kyb agx shocks

Now this setup rocks! full lock is wicked. no rubbing, does a circle like crazy, road feel and steering response is sweeet. i want to shorten another set MORE and see what happens. next project is to make some rear traction brackets and weld up a panhard bar.

[SoSideways]

Originally Posted by GripTerror

i have spl tie rods and the flcas and tie rods were parallel.

That being said, the car felt bumpier, shittier, rolled more, was more out of control. it was all quite pronounced and noticable. Raising it back up, car felt more controllable, more compliant, significantly less roll, etc... That's why I want the geometry all corrected properly while get the benefit of being lower (from a functional not look perspective). I don't drift, I track for lap seconds around a road course.

That's just a function of messed up geometry, not tie rod/tie rod end related shittiness.

I thought you meant that your car's bump steer was worse after you fixed the arc...

But to be honest, unless the FLCAs were also spaced down via roll center adjusters or whatever, the tie rod ends shouldn't be spaced down either, since that'll create two different arcs and could cause bump steer to get worse.

Anyway, fix your roll center and make sure nothing is binding up man.

[GripTerror]

Awaiting anxiously mmdb's review on driftworks stuff.

[PoorMans180SX]

Originally Posted by GripTerror

Awaiting anxiously mmdb's review on driftworks stuff.

Me too. Interested in seeing the correction at a really low ride height as well. Hopefully he can slam the car and give us some pics of the arm angles.

That video of the Tomei/Cusco Impreza has me brainstorming, and I've been drawing up some stuff.

[mmdb]

Originally Posted by 240sxaddict

To be fair my question was vague and sounded very lazy. Sorry!

All good. Internet is ambiguous like that.

Originally Posted by GripTerror

Awaiting anxiously mmdb's review on driftworks stuff.

I'll be sure to take lotsa pictures and compare them side to side with the GP Sports, OEM, and Driftworks knuckles as well as the angles when they arrive.

[racepar1]

The driftworks stuff is likely very good, but for THAT much money the damn things should come with sphericals. I'm willing to bet that that is the only gripe that anyone will have about those. The design looks pretty damn good, though I do wonder how heavy they are.