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Roll Center.....again

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  • Roll Center.....again

    Ok, so I've been brain storming with a friend on making some adjustments to the front control arms. We decided that a rod end - like the battle version weld in kit - instead of the rubber bushing would be ideal for the main mount.

    To my knowledge (although very limited) roll center can be adjusted in two ways. By changing one of these two things (green and blue highlighted areas):





    We were going to cut up a control arm and see if we could weld the green highlighted part up higher while keeping all of the factory angles that are supposed to be there. Basically cut and weld some metal in there to increase the height of where the factory sized ball joint sits, and effectively change the angle on the arm itself.

    I just wanted to run that by you all on here to see what the general consensus is. Will this actually work? We'd basically measure the angle of the arm and figure out how much metal needs to be added to make the arm parallel rather then angled upward from excessive lowering.

    Any help or advice is greatly appreciated.

  • #2
    Is there supposed to be a picture here?

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    • #3
      being that you guys are discussing knuckles & rollcenter adjusters, i'm curious to know if any body has used the GP Sports Hyper knuckle kit/ Super knuckle kit- heres a link to their web site http://www.gpsports.co.jp/otr/knck.html

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      • #4
        roll center is determined by the location of the PIVOTS, more specifically the center of the rotation. so for a heim joint it is the center of the hole, and for a balljoint like the lower control arm has it is the center of the ball inside the balljoint.

        This being the case the shape of the arm makes no difference.
        Therefor what you need to be changing is the distance from the axle (on the spindle) to the center of the ball that connects the spindle to the lower control arm.

        basically what you want to do to get the roll center under control is move the ball part of the balljoint or heim physically DOWN in relation to the axle.

        If you're doing this with a heim joint what you need to do is make some sort of spacer that attches to the SPINDLE, which would space the heim downwards, and in doing so make the lower control arm flatter.
        again i point out the the arm itself isnt the important part but the line from the inner pivot of the lower control arm to the outer pivot of the lower control arm (the heim).

        if you dont understand this description google image search for roll center, and see how its a series of lines connected to pivot points. all that matters is that the points are connected with something, doesnt have to be straight, could be u shaped, so long as the pivots are connected by fixed "arms".
        so modifying the arm does nothing, other than change the strength.

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        • #5
          So, in short, of the two methods of changing the roll center I posted, the only thing that'll really change the roll center is the blue highlighted bit - or completely changing the arm altogether (rod end w/ height adjustability)?

          Thanks for the info!

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          • #6
            Don't think of the physical shape of the arm, imagine a straight arm between the pivots and you want to change the height of one end or the other.
            '18 Chevrolet Volt - Electric fun hatch for DD duty!


            DefSport Koni Sleeve and Spring Perch Buy!!!
            http://www.nissanroadracing.com/showthread.php?t=5902

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            • #7
              Thanks Def, that makes perfect sense. I'll let you guys know what we come up with....there might be several months of silence, haha.

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              • #8
                Interesting, but try not to be silent :P
                "hexa-dodecahedron-triple-threaded-super-eleventy-way-adjustment-spec" dampers. -Def

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                • #9
                  My friend that I am brainstorming with lives ~1.5 hours away from me so we basically communicate through a thread on a local forum (including pictures) and the phone, haha.

                  He just so happens to have a S14 and S13 in his garage, on jack stands, without motors or suspensions....so he was able to get pictures immediately and he happened to have a nice set of calipers to do some measurements with.

                  It's looking good so far - he works very early in the AM so I have to wait for him to get back to me about a few other things before I post on here. As I don't want to post incomplete or inaccurate information.

                  IF I am interpreting the pictures correctly that he sent me there should be a couple of INCHES of space to move the mounting point. I'll post up when I find out.






                  I guess I'll ask one other question. I've been assuming the entire time that the goal of correcting the angle in the control arms is to get them to be parallel with the cross member? Is that, in fact, correct? I found a way to actually measure the roll center online - but I believe the amount of measurements it requires may be outside of my ability. Even if I did get the actual number I wouldn't know how to apply it - like what a "good" roll center is, haha. If anyone can shed some light on that for me I'd appreciate it.
                  Last edited by WishIHadaSilvia; 11-05-2008, 08:52 PM.

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                  • #10
                    Here's what we're thinking right now - converting the FLCA bushing end to a rod end so we have some length adjustment as well and it will give you around an inch of space to move the mounting point up. Here's the pictures so far:



                    The red/blue/green dots are just areas I wanted him to look and see how much space was there for the arm to actually move.



                    There is room to move the actual stock arm up some, I am thinking the rod end will free up a little space. Would it be safe to grind one of the edges of a rod end down to allow for more clearance? I am thinking no, but just figured I'd ask. Also, what kind of loads does that particular spot see?




                    From the thread about the JIC time attack S15 I got this picture:



                    It looks like there is enough room to move the rear up some as well. It actually looks like the factory position could be cut off and a new, taller/stronger one could be welded in its place.





                    We're working on some spindles as well. I know this will not interest the majority of the people here as they're for angle, but I just wanted to be sure I am grasping this properly.



                    If the tie rod mounting point is kept on the same Y and Z axis the steering input should feel the same right? Basically, I'm trying to find out if spindles can be made that have the same steering feel as a OEM unit but achieve more angle. Changing the X axis (black line in my picture) will change the angle yes? And leaving the mounting position in the exact same place will keep the steering the same right?

                    Please correct me if I'm wrong.

                    I know the RX-7 guys do this:



                    and get angle like this:





                    I want to make a spindle like that so I have options (factory position or super wide angle position).

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                    • #11
                      Although I don't grasp all of it as yet, this is looking awesome, ambitious and worthwhile. But know this forum is mostly anti-drfit and pro-grip hehe.
                      "hexa-dodecahedron-triple-threaded-super-eleventy-way-adjustment-spec" dampers. -Def

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                      • #12
                        I think drilling new holes in the subframe is a great idea. I'm going to check into that and see how difficult it will be to get those holes drilled perfectly.

                        Any of the suspension gurus want to take a shot at how much the arm needs to be moved, relative to how much it has been lowered?

                        Is moving the roll center by itself going to effect anything else?

                        I'm going to be picking up a few spare subframes for my engine swap project and I don't mind drilling these holes to test this idea.
                        Last edited by jmauld; 11-06-2008, 12:47 PM.

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                        • #13
                          I had to take my front wheel off to check for a nail today, so while I was there I decided to stick my head in by my LCA. There is so much room it is kind of ridiculous. I could fit two fingers in there and move them around easily. It looks like even in line w/ the factory location the arm can be moved up around 1/2 of an inch. If the arm is shortened and the hole location is moved an inch or so out there is even more room to go up.

                          I'm pretty excited about this and hopefully will have something done by this weekend - as my buddy has those cars up in his garage and is willing to start drilling.


                          We were going to get the cars on a lift that keeps the suspension from uncompressing - like an alignment lift - and take some measurements/use some string to get some numbers and see if there's enough space to completely correct the roll center.


                          I still would like to know what an ideal placement would be for the control arms - preferably an angle they need to be at. This way it can be applied to all S chassis and the only thing that would have to change is just how much the arm needs to move.

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                          • #14
                            Originally posted by WishIHadaSilvia View Post

                            We were going to get the cars on a lift that keeps the suspension from uncompressing - like an alignment lift - and take some measurements/use some string to get some numbers and see if there's enough space to completely correct the roll center.
                            Alternatively, you can lift the front end, remove a strut and move the arm through as much motion that would reasonably represent the real world. Measure how much you can move the arm up at full compression.


                            I still would like to know what an ideal placement would be for the control arms - preferably an angle they need to be at. This way it can be applied to all S chassis and the only thing that would have to change is just how much the arm needs to move.
                            Don't fall into the "ideal" placement trap. Moving it up 1/2" may not be ideal, but it's likely better than it is now.

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                            • #15
                              I just looked at my spare crossmember. The first problem you'll run into is that on the back side there is a bracket and the associated weld that is probably going to be right where you want to drill your hole.

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