I was reading through some of the old threads on the 6-link rear suspension mods. One advantage sited was the lack of camber change as the suspension traveled up and down. This was deemed good if you were going in a straight line, but not so great if you were going around a curve, as the body roll would induce camber.

My question: what if the top and the bottom "links" were not the same length? Wouldn't that work similar to unequal length A-arms? Where as the suspension is further compressed, the arms force the top of the tire to "tilt" in toward the centerline of the car...

Just curious as I was trying to visualize in my head...

:crazy:

 

Yes. If you have a 6 link setup (assuming you have a link above and one below the halfshaft) you would want them to be of unequal length if you want youor car to handle properly.

I'm actually curious to know what's so bad about the camber change of the suspension as it is. The cam link is longer than the driveshaft I believe and it will serve to resist camber change while cornering.

Consider that for an equal-length A-arm setup the camber ratio between the body and wheel will be 1:1. If the body rolls 1 degree, the wheels will camber 1 degree (toward the outside of the turn). In a typical unequal length A-arm setup for the front suspension, 1 degree of body roll will result in 0.85-0.90 degrees of camber, still toward the outside of the corner. Does that little bit make a difference? Sure does!

Now I'll toss an idea out to you. What if you had a semi-independent suspension in the rear of the Vette where the wheels ALWAYS stayed vertical? Take our rear suspension. Tie the wheels together through the use of a tube that goes from upright to upright. Ditch the camber rods. The wheels stay at the cambered orientation you placed them. You end up with a De Dion suspension. It looks something like this:

 

Basicly you and ddecart are right.
My car will be lowered to the max so that the halfshafts will be horizontally.
That´s the biggest problem with the original suspension.
According to my drawings the original suspension increases camber about 2° during 12° wheel rotation. You won´t be able to adjust camber right, because the halfshaft was never ment to be that horizontally = normally the suspension is allready compressed, meaning that the increased camber is already in at normal driving conditions.
We need an increase in camber during cornering, but this again depends on body roll.
If you´re running big stabilizer bars, you won´t have that much body roll, and the increased camber over wheel travel can be achieved by screwing out in the heimjoints (allowing to set the strut rod length)
Of course you are changing normal camber too, so it´s only a few degrees.
I don´t know how much ° body roll my car will have and I always stated that my system wasn´t tested.
I have the ability to make my own parts, so I can easily say okay, let´s move the lower rotating point a little towards to the center by increasing lower strut rod length to get more camber over wheel travel.
Hope this was not too confusing ;)


[Modified by MARKUS_P, 12:19 AM 10/15/2002]

 

Markus

It looks like you also installed a block between the differential and the lower control arm bracket. I did this too some time ago. My lower contol arm or strut is now parallel with the half shaft. My tires stay within about 1-2 degrees of vertical as they go up and down in the wheel well. With the heavy duty springs and shock, body roll is pretty minimal, so I am happy with the setup. The more roll I have, the thinner I would make this shim since the camber change can offset the body roll in a turn.

Chuck

 

DeDion is a neat setup. It is used on the Super 7's is it not?

I am a little confused about the 6-link conversion. How come the upper link does not over constrain the wheel? Are the IC coincident?

Any close-up pictures? I would like to make a computer model to analyze the motion.



[Modified by Turbo-Jet, 11:10 PM 10/14/2002]

 

Chuck, you´re exactly right about this.
I didn´t use a block between diff and lower bracket, but I moved down the rotating point to achieve a parallel setup like you did.
In my case I nearly got zero camber change.
Body roll will be minimal with my setup, 550 coil springs front, 340 lbs spring rear, big stabilizer bars and bilstein shocks.
But never the less I will have to test it out - it´s all theoretical.
I just had a look at my construction - movement drawing.
It shows, that if you have lowered your lower roating point as you did, the lower strut rod length isn´t that important.
With the original lenght I get 1° camber over travel, with shortened 0°
Maybe I´ll make lower struts a little longer if body roll should be bigger than expected and if my pre camber setup isn´t enough.

 

Originally the half shaft was the upper strut rod.
Now the halfshaft is forcefree and slides in and out of the diff during wheel movement.
So forget the halfshaft and concentrate on the upper and lower strut rods.
If they are a perfect parallelogram camber is zero during travel assuming zero body roll.
The upper link doesn´t constrain the wheel as I understand how you thought about it.
I´d try to get the setup as near to a parallelogram as possible, then choose your lower strut rod length for increase of camber over wheel travel. Because of it´s bigger roating radius the lower rotating point is traveling more out then the upper roating point with the smaller radius.
Thus increasing camber over wheel travel.
The other way is to NOT lower the lower inner rotating point, which makes even more difference in camber.
Practicl tests should clear that up I think.
Once again this is all theory, but if chuck says he´s happy with his setup, I believe him although he has nearly no camber change over wheel travel.
But he has nearly no body roll ;)
:cheers: Markus

 

So the differential output shafts have to modified to accommodate the change of length between the spindle and differential? (use CV’s :p:) How is this done? Stock rear suspension requires that the halfshaft is a loaded member, under compression/tension (aside from drive torsion), correct?

By making the 6-link upper and lower links parallel, the rear IC goes to infinity. What does this do the roll center?



***pic fixed



[Modified by Turbo-Jet, 3:10 AM 10/15/2002]

 

Yes, the spindle has to be modified.
Remove the c-clips that holds the spindle in the diff, take the spindle out and machine the shaft until the c clips groove is gone.
Some prefere to not machine the spinde and simply take out the c-clips.
I don´t agree with them because the spindle may limit the movement to the center of the diff. Then you have big trouble.

The rear inner center goes to infinity.....that´s correct. If it don´t go to inifnity you would have a camber change over wheel travel.
What does this to the roll center? Good question....
The roll center is lowered (in my case appr. down to the height of the lower strut rod)
Normally it would be much higher
Now the next question would be is it good to lower it?
I´d say yes, because the higher the roll center, the more is the wheel moving inside (in direction to the diff) reducing track (do you say track in english ? I mean the distance between both rear wheels, the width if you want to say so)
Hope this helps :cheers:
I just saw your drawing, had to play around a little because first I saw only xxxx.
You´re getting roll center different than I do.
I mark the middle of the spindle and follow it´s way through the wheel travel. Then I lay a curve through the marked points and get a circle with a center point. That center point is the roll center, at least what I call roll center.
Your technique is interesting and I´ll check out if it works and if we get the same results (as long as the rods arn´t parallel because then you will have problems finding the instant center :lol:





[Modified by MARKUS_P, 4:40 AM 10/15/2002]

 

As the IC approaches infinity, the roll center approaches ground level. I have to review some of my books, but I also believe that this is not a bad change in geometry.

Parallel links of approximately equal length will result in zero camber change under vertical travel, but chamber will change with body roll, unless the relocated roll center compensates for this effect? To what extent I wonder.

Just for thought, what if the lower links were pivoted at the center, under the differential? Like SLA suspension, reducing camber change during vertical motion, but have better geometry upon body roll.

Also, how does the new upper link affect scrub radius?

Has anyone measured the co-ordinates of the stock suspension points and aftermarket modifications such as this 6-link, and the smart struts? I would love to run some simulated analysis and compare data. I find this stuff fascinating.