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PostPosted: December 23, 2018, 5:22 pm 
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Long A arms that cross over the chassis centerline?
Thought I had posted this idea before but could not find the thread.
Maybe it was another forum.
Sitting around on a cold day day today, staying inside, and looking out the window at my Trick-6 body.
Not satisfied with the very short rear A arms I will be forced to use unless I come up with something fairly radical for the IRS.
Looked up the Ford "Twin I Beam" system which verified that something similar has been done commercially. :D
So my idea should just be a matter of clever packaging.
I easily understand the draw of longer arms, less change in camber for the same movement.
My likely suspension parts have upgraded? to "Mustang/Wilwood" brake bits with vented rotors from a bent Alfa-Romeo race car.
This forces me to change to larger 15" wheels :( but also allows much bigger brakes.
I also got some NASCAR type hollow torsion bars so may be able to eliminate coil springs, if I have enough ground clearance.
Drivetrain is a warmed up Buick 231" V6/V8 WCT5 and Merkur diff.
Not crazy LS power but certainly enough to get me in trouble. :wink:
Just a street car but I do want to hill-climb it and run the Silver State Challenge so superior handling/braking is a must.
Going to look around for some material to make models from as that will be easier than getting back up to speed on CAD.

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PostPosted: December 23, 2018, 10:46 pm 
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RichardSIA wrote:
Long A arms that cross over the chassis centerline?....



One or both?

Make your string computer and play along to see what better fits your goals.
There´s no one solution for all scenarios...


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PostPosted: December 24, 2018, 3:37 am 
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Both, for equal length.
No matter what I do the tricky bit is getting it to all fit without cutting out the floor.

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PostPosted: December 24, 2018, 7:49 am 
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Most mid and rear engine cars with IRS have rather short lateral control arms. Considering that this includes some of the most stratospherically priced cars in the world, if it was really that beneficial to go to such lengths to lengthen the control arms, it probably would have been done on more cars. My guess is that any potential gains aren't enough to warrant the added effort, or are more than offset by other potential losses, and would probably be better off just trying maximize their length within more conventional packaging constraints.

The Twin I Beam is not exactly the hallmark of good handling. I haven't worked through the math on such a beast before, but as applied through a double a-arm type suspension, at the very least I think it may have some funky Roll Center effects. Consider that the inboard body mounts on both side of the car all typically move the same direction as that side of the car, outboard suspension mounts move down when the outboard side of the car rolls down, and vice versa. By switching sides for the mounts, the the outboard suspension mounts would move up with the inboard side of the car while the outboard side of the car rolls down, and vice versa.

That being said, considering my rear suspension plans, I have little room to judge...So by all means, give it a try and see what happens.

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Last edited by Driven5 on December 24, 2018, 4:46 pm, edited 1 time in total.

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PostPosted: December 24, 2018, 9:17 am 
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Ditto on the Justin remarks!
The only reason for a twin I-beam was lower cost Vs a REAL suspension system.
DaveW


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PostPosted: December 24, 2018, 10:38 am 
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davew wrote:
Ditto on the Justin remarks!
The only reason for a twin I-beam was lower cost Vs a REAL suspension system.
DaveW

And here I thought that the Ford Twin I-Beam was just an evolutionary change from solid front axles while still keeping the kingpin. Given either scenario, it wasn't put into passenger cars to my knowledge. I doubt that anyone at Ford wanted to do that.


Think of it. In a Twin I Beam vehicle in body roll would lift the body pivot doing the exact opposite of camber gain. That could be overcome with an over-long lower A-arm, but why, I ask, would I want to?

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PostPosted: December 24, 2018, 2:19 pm 
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To be clear, I am still looking at upper and lower A arms, just not the conventional mounting.
I will look into the point made about reverse pivot movement, maybe the upper arm ends up longer than the lower?
At this point it's just a doodle, idle speculation that I will try to pursue in the evenings.
Need to play with CAD before I forget how entirely. :BH:

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