Technical 4 Bar Parallel Rear Suspension Question

I did a bunch of searches but I didn't find what I was looking for. What is the minimum acceptable distance between the bars (side to side) on a 4 bar parallel rear suspension? What is optimal?

Thanks for your help.

Rock

 

There will be less deflection and strain the wider you place them.

 

Yes, I know that but I'm trying to figure out If 32" is ok, or 36". How much difference is there going to be, say if I go 32" instead of 36"?

I'm working with an X frame and I am trying to fit this with a minimum of frame mods. See this thread.

http://www.jalopyjournal.com/forum/threads/49-buick-rear-suspension-upgrade.930112/#post-10481434

 

Not as big an issue if you aren't racing it, just go as wide as is possible. Could also do like a lot of Buick guys have done on torque tube swaps and install truck arms. Just need to re route the exhaust near the rails.

 

With that Chevelle body style rear I would use the upper trailing arm mounts that are on the rear already and the truck arm on the bottom, I know that wasn't your question. The distance on my MG is 24" but of course the tread width is only about 48". 32" will work out as opposed to 36" if thats where it fits on the X-member call it good.

Pat

 

I think you may have misstated your recommendation.There is no way that it is feasible to use truck arms on the bottom and also utilize the upper bosses with diagonal control arms. The truck arms do not have pivots, they are securely mounted to the axle housing and, so being, do not require any additional control arms except for a Panhard bar. The combination of pivoting upper arms and non-pivoting truck arms at the bottom would make for some very interesting, and stressful, counter forces.

 

Rock, In my opinion.........the horizontal distance separating the 4 bar setup is less important than the placement of the springs/shocks, or coil overs, insofar as body/chassis roll control is concerned.

That said, I would place them as far apart as chassis dimensions allow. Just inboard of the chassis main rails, as you saw in the photos in an earlier post seems to be adequate for normal driving.
Autocross may require more attention to geometry

 

You would likely have about 1"-2" of suspension travel, maximum, until you broke something, horribly.

 

Ray, that was exactly my thoughts. I just wanted to get some opinions. As with all requests for information, you have to filter out some of them.

I have a Chassis Engineering rear sway bar that I would like to use, if I need it. The length on it is 36". Obviously, I can't have the 4 link at 36" and the sway bar, too. So, I'm trying to think ahead and plan my system out so that I have all of the flexibility I may need. I hope I don't need the bar, to tell the truth. They get kind of messy with 4 bar setups.

 

I mentioned truck arms but was thinking about the pivoting arms that are used on the bottom of those rear ends on GM cars my mistake.

Pat

 

Um...why not ?

Both the parallel arms should be as wide apart as possible, and the Panhard bar should be as long as possible.
If they both end up at the same width/length...so what.

Note, all bars should be parallel to the ground at ride height.

Mike

 

Because the drop links for the sway bar cannot go through the suspension bars.

 

Not necessarily.

 

Can't flip it and have the links towards the rear? Here's one of the truck arm threads I was referring too. http://www.jalopyjournal.com/forum/threads/348-in-a-50-buick-swap.588761/page-2

 

Gas tank and panhard bar is in the way. I read the truck arm threads. Thanks, but I just think the 4 bar fits my needs best.

BTW, Brock at Morrison said they do installs as narrow as 24". He said going down to 30" was no problem but keep it as wide as possible. I should be good.

 

Gimpy -

Well, they should be very close for the best suspension movement..!
I don't think rockable is talking an adjustable NASCAR Panhard bar or drag racing 4-link suspension..!

And for what it's worth, just because someone sells something, doesn't mean it's a good design. Those little short bars can really screw with the handling if the car has somewhat normal up and down suspension movement.

Mike

 

A properly configured 4-link sets up the roll-center, and its relationship to center of gravity, and instant-center.

The panhard bar should be level, loaded, with a half-tank of fuel. After that, the angle of the 4-link bars should be set up for both proper roll-center, and proper instant-center.

Parallel and level works, but is far from ideal. You are leaving good handling, and a good launch, on the table, unrealized.

 

Heat them up, and bend them around.

 

Launch is not as important to me as roll steer. This is a cruiser.

 

Suit yourself.