Technical Rear Suspension/Ladder Bar Question.

As a Drag Racer I am used to seeing parallel ladder bars that are roughly 1/3 the wheelbase. Why do most hot rodders use long triangulated ladder bars? I know the long bars will be less aggressive. Is it the vintage look like a wishbone or are there other advantages?

 

Its street rod chit. The long triangulated bars don't need a panhard bar.

In a perfect world I like my ladder bars to land somewhere close to where my front U joint is length wise. On some cars depending on set back and transmission length that can be pretty short. LOL

 

Traction control is not what the bars are for, they are for locating the rear end.

There are a few serious cars that have drag race style 4 link, or shorter ladder bars.

 

I think it is because the geometry of triangulated ladder bars do the job of controlling axle ‘wrap’ and location without the stress induced by parallel bars. For drag racing, suspension flexibility is not so much a concern as with street driven vehicles. For street, body/chassis roll is usually more pronounced with more compliant suspension. That movement with parallel traction bars causes a twisting action that tries so rotate the axle housing, like a anti-roll bar, but can’t so it either bends or breaks the traction bars. With the triangulated bars, they act more like a wishbone and eliminate, or more often minimize, that rotating force. The closer together at the front, and the softer the bushings, the less destructive force and better suspension movement occurs.

Ray

 

To a certain extent, it's a legacy from the early torque-tube closed drivelines. The pivot point for the suspension needed to be located very close to the trans/driveshaft pivot to prevent binding, plus the frames weren't designed for the 'twist' that would be caused by moving the points outward.

 

I like to build my own. 1 1/16 DOM with 3/4 rod ends.



The trick to running them on the street is angle them in at the front so they let the rear end roll up/down when you hit bumps. If they are parallel to the frame rail, the rear end becomes one giant anti-roll bar and starts breaking stuff.

DON'T LOOK at the mufflers, they did not stay.



-Abone.

 

Advantages -
Works
Simple and clean
Easy
Fits
Hooks

Plus it sorta looks like the frame was designed for a wish bone style rear end locating mechanism

 

As tight as I could make it on my '31

 

I used Jegs ladder bars to locate the 12 bolt in my 62 Tempest, cuz it was the easiest way. I hated driving the thing because of body roll issue , or lack of, I should say. It aggravated me, just going in and out of the driveway to the street. It did it's job, running in the 11's as a street car, but I only kept it for 2 years.
If I did it again, I'd design a diagonal 4 link with semi-hard bushings and an instant center point where it would still do it's job but ride like a GTO.

 

I have almost identical adjustable ladders as Mark Yac on my '30 w coil overs and top mounted panhard....spherical ends except solid fronts....no issues. I do take it easy in and out of off level entry/exits like gas stations, driveways....but on the road never been a prob. I check things regularly to ensure no bending or stress probs

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I used a modified Pete & Jakes triangulated ladder bar set up shortened from a Model A kit in my old Street Morris Minor. It hooked great and rode good too. I had a panhard bar on it and a rear sway bar.
My new Mor ris minor will get these home made ladder bars ,but they are drag race only.

 

Traction bars main purpose is to prevent spring wrap, hopping tires and loss of traction. for that purpose it doesn't matter how long they are. Good old cheapie 'slapper bars' so a pretty good job of this on leaf springs rears. Ones using ladder bars usually do it with coil springs which won't bind like leaf springs will with fixed ladder bars which necessarily travel in different arcs than compressing leaf springs. Stop and think; even with coil springs if the bars are anchored to the chassis in front of the axles, short bars will swing in a small arc so as the springs compress the rear wheels will move forward and backward in the wheel well. This could cause problems. Long bars will travel in a longer arc thus the wheels will go pretty much up and down and not forward and backward.

On my Willys I wanted the look of the big ladder bars but still wanted to run leaf springs. I solved the problem by mounting the front of the bars in Mustang II front end control arm rubber bushings with 3/4" pipes welded into the bars that can slide to-and-fro but still prevent tire wrap. I welded the mount to the tranny X-member which was a convenient place. For my buddy's '42 Willys pickup we did pretty much the same setup except we used a short link with heim joints on each end, with an appropriate bracket welded to the forward frame to allow the bars to move forward and backward but not up and down.

The triangulated setup is necessary for room on the common really low cars nowadays and does provide axle centering function. I would still run a pan-hard bar too but as I get older I am temped to wear a belt and suspenders so don't listen to me! Again, a pan-hard bar needs to be as long as possible for the same reasons; longer means less left and right displacement as the axle goes up and down. A better solution is a Watts linkage (bottom photo) which eliminates the left and right movement but centers the axle while freely moving up and down. There is no advantage to the triangulated setup in the traction improvement task.

 

Well...sort of. The drag racing guys also want to plant the tires (assuming they're doing "modern" drag racing with sticky tires). So the suspension design can make quite a bit of difference, and things like lengths, angles, pivot locations, and even spring rates and shock damping rates, may need to be set up just right

 

Every circus needs clowns and acrobats. The clowns are entertaining but with timer a man's desires become more refined and he prefers the acrobats.

I suppose that a car that just stands up and cuts a straight line is not much for the spectators, but if you are serious about getting to the big end that is the car that you want. one that the suspension is set up right, no muss no fuss.

Back to the original topic, the triangulated ladder bars are just a street rod version of a truck arm suspension. They work and are not as harsh as a race tuned ladder bar setup.

 

I'm not real good with custom suspension stuff. Why the watt's link with leaf springs, ladder bars and sway bar?
Seem like a lot of stuff holding that rear in there.

 

It depends on if you are using them to just connect the rear axle to the car and look good or if you are actually intending them to aid in traction. The latter would be dictated by wherever you have the instant center located on the car. Usually if used as traction device the bars are made pretty short for strength and adjustibility of pinion angle and Axle relation to the instant center of the car. Basic rule for Ladder bar VS 4 link is car weight. Cars up to 2800 lbs with drive work best with 4 link. Latter bars are chosen for cars over 2800 lbs with driver...blah blah blah.... you get the idea.

 

A common ladder bar setup has adjustability built into it for adjusting your instant center. Instant center on a properly built setup ( for racing not cruising) is determined by length and bar angle.

Here is a pic of a setup for a more modern chassis.


Ladder bars are not as forgiving as a 4 bar setup, IE a 4 bar articulates better. On a short wheelbase car you can ever lift a wheel going over a bump at an angle. Gives me a chuckle, we knew a guy back in the late '80s that set his Mustang II up with ladder bars. He was still running an open rear but it looked cool and looks is everything right? He got it stuck pulling into a driveway. Lifted a wheel and that was all she wrote.

 

Thanx P&Br

 

With the fact that you have a non compliant (heim joint) connection at the front of your bars you still have created a truss that will use the rear end housing as an anti roll bar. The P & J package relies on the close placement of the front mounts and the compliance in the bushings at that point to allow some body roll. With a rigid front mount (heim) the only way that the chassis can roll laterally is if the arms meet at a single point ( hmmm! Sounds like the original Ford torque tube/wishbone) or if the frame or bars flex.

Roo

 

I presume that there is some sort of mechanism pivoting on top of the Watts linkage mount to operate the shocks.
As for the disparate arcs of leaf springs and ladder bars the most common solution in drag racing is a slider mount connecting the housing to the springs. There was plenty of info here on the HAMB about 4 years back: https://www.jalopyjournal.com/forum/threads/floating-axle-housing.821957/

Roo

 

I am not sure that I understand the question.

In this picture, the shock absorbers run in front of the axle.

They do not interact with the Watts link. I have never seen a Watts link that interacts directly with the shocks.

 

That P&J set up with an extra gusset is good for 9 second runs. Not too shabby for "street rod" parts.

 

OK, looking at the photo on my big monitor I can see that the vertical rods are the anti roll bar links. Even with the red highlights it is a bit hard to see where the shocks mount and what they connect to. I was assuming that the photo had some relevance to you Willys comments but I see now that it is just to show a Watts package.

Roo

 

Yes just a photo I grabbed off the internet to show the Watts linkage. No implications intended for the other suspension parts in the photo.

 

That is one ugly rear end set up!

 

Extra gusset in the bar,
Running 9.90s

 

it doesn't take much to run 9.90s, I do it with leaf springs and simple looking traction bars.

 

Well . . . rear ends are generally ugly!!

 

You are correct, but mounted in the car, there was enough roll in the ball of the rod end to live a happy long life. You could jack up one rear tire and the rear would articulate enough to keep the other on the ground. Lots of stuff we do is a compromise and most rear ladder bar set ups are a pretty good example.

-Abone.

 

More than a handful of 7 second cars on this simple set up.



-Abone.