I have the "small" drag bars and can tell you these suckers are nicely overbuilt! No weak points I can see and I can't imagine your needing anything bigger.... but it's your choice.
Prices here...http://www.lazarsmith.com/science.html

RJ

 

RJ-- I ask because most of these bars are stronger in tension than in compression. Tension tends to straighten the bar, while compression will collapse a bar more easily if there's a bending moment of any kind (which there should NOT be in a properly designed bar, as these certainly appear to be).

The other thing is that loading the bars in tension would put them above the axle, not below-- which would be more favorable off-road wrt approach/departure angles. The problem is that putting the bars above isn't really that feasible, imo. PUtting the bar below allows a plate to be fabbed that can slide under the leaf pack, as the Lazar kit apparently does. This is a lot more practical than trying to weld things onto the axle tubes, imo.

Let's talk leverage. Axle wrap is simply the axle housing twisting along it's rotational axis-- it's the whole "equal and opposite" reaction to the action of putting power to the ground. If you mount something to the axle in an effort to eliminate the reaction (more accurately, to absorb it so the springs don't), then it will experience a torque. Hence, leverage matters.

What this means is that the distance from the link attachment point (at the axle) to the axle centerline becomes critical. If you attach the link too close, the the joint is loaded very heavily, and any play in the connection is amplified by the short lever arm. This means a less effective bar that's under a lot more load (which EITHER means it's more likely to fail, OR it has to be made a lot stronger to be as reliable).

But if the link attachment point is too far away, installation becomes pretty impractical, and you run into suspension binding issues because the travel arc of the traction bar deviates too far from the normal axle travel path.

See, axles tend to go straight up and down-- hence the slip yoke at the t-case to allow a change in shaft length as it travels up and down. But traction bars will follow an arc whose radius is the length of the bar.

Now, the longer you make the bar, the closer that arc becomes to vertical and the less likely you are to have binding issues.

So my thoughts on bars in general:
-- Make 'em as long as you can
-- Mount them to the axle as far away from the axle centerline as is practical for your application (obviously, pavement pounders and off-roaders have different needs for ground clearance)
-- the attachment at the frame needs to be located based on the normal ride height of the rear, because you need to "optimize" the bar's arc plane based on the suspension travel. Imagine you're looking at a compass face, with North at 0° and South at 180° and so on. Say that the suspension travels a 5° arc- Should it travel that arc from 245°-250° or from 225°-230°? This is determined by the attachment point at the frame, and how close to horizontal the bar is positioned at rest. This is all the more reason to make the bar as long as possible-- the longer the bar, the fewer degrees the arc is (a narrower sliver, if you will) and hence, less likely to bind.

I haven't looked all that closely at the Lazar bars design-wise, but they look very well done to me. In the end, the reality is that even after the real world forces significant departures from the "ideal", even a "compromise" bar is still MANY MANY times better than none at all!

I remember when Steve St. Laurent of TDR was first trying to get some effective traction bars to market-- 5 years ago! There was and is a huge need for a product like this. The factory suspension leaves a lot to be desired as far as stability goes, and these Lazat bars no doubt are a huge improvement!


Justin

 

JH... I must be getting older and wiser. I followed all that the first time through.

I heard much of the same from XLR8R when he said he had studied the geometry of 'Bars' to eliminate any possiblity of binding.

One point not clear? Are some bars set up for tension? (pulling on the axle) instead of pushing. If so...Why?

RJ

 

Some bars are, in fact setup for tension or "pulling on the axle" instead of "pushing". The advantage of this is stability. It's like a rope-- can you push or pull better with a rope? Now, obviously a rope has no rigidity, so it's not a fair comparo-- but the idea is that compressive strains tend to introduce deflection (or cause a bent bar), while tensile strains tend to straighten the bar.

One example of compressive strain is standing on a typical aluminum can. If there aren't any dents in it, you'll find that the can will often support the weight of a person on one foot. Yet, you flick the can with your finger and you get catastrophic failure and it's squashed flat.

Assuming you can avoid deflection, compression is a VERY strong way to bear load. But it's also very shape-dependent, as the pop can illistrates. Once the can is no longer a perfect tube, it fails.

Tension loading has a couple advantages to me. First, it's not subject to the deflection issues of compression loading, as the tension tends to straighten. Hence, a failure in tension tends to be gradual-- not catastrophic. If anything, might stretch the bar, but it won't break. That's another advantage: the tension loading takes advantage of the elasticity of the bar. The Bar can stretch rather than break, and this helps it manage strain a little better. Moreover, you can install the bar with a little bit of "preload" to take up any slack, making the install nice and tight. I'd do this by making the bar just a tiny bit too short, say 1/4 inch.

Because of the way the axle wants to rotate, the bar has to be above the axle housing to be in tension. This enhances ground clearance, but can cause interference problems-- there's not as much space above the axle tube as there is below it.

So, in my mind tension is "ideal" but much more difficult to implement, and makes for a hassle to install. Properly done, compression works just fine and is much simpler to package and install.

One final word on bar shape. The "ideal" bar for tensile loading and compressive loading look very different. In tension, the shape of the bar matters little-- as long as you have enough meat to share the load. So if you have 1 square inch of sectional area, tensile loads don't care if it's a small diameter solid bar, or a large diameter thinwall bar.

Compressive load is much different. For compressive loads, rigidity matters a lot, hence a much larger diameter bar (with thinner walls) should be used. A solid bar in compression will have poor rigidity, and isn't a good choice. Much better to have a 3" bar with .080 wall than to have a 2" .120 wall for compression. This assumes that the bars won't get dents in the walls!

Hopefully this better illustrates why I favor tension loading (pulling on the axle) rather than compressive loading (pushing).

Justin

 

OK, I thought I was done, but I'm not

I must take issue with the claim that the bars act as an anti-sway bar.


Anti sway bars perform as they do because there is a linkage of the left side to the right side in terms of suspension travel. In other words, the left side can't flex without the swaybar also trying to force the right side to flex in the same direction.

Hence, the term "anti-roll" because in a turn, the outside wheels will compress and unload the inside wheels. The anti-roll bar transfers the compression of the outside to the inside wheels-- essentially tranferring the center of gravity back towards the middle of the car when cornering forces attempt to push it to the outside, or at least fighting the transfer to begin with.


Because the Lazar Bars do NOT connect the left side with the right side at all, the CANNOT perform the function of a sway bar. If they did, then jacking up the right side of the rear axle would cause the left side to raise as well. This is why the off-roaders often remove sway bars, because they link the two sides together and make the travel of one side related to the travel of the other-- which reduces suspension flexibility. There's a reason the new Power Wagon has a front sway bar disconnect!


Now, it's possible to have the EFFECT of an anti-roll bar without the ACTION of an anti-roll bar. For example, I can drastically reduce body roll by making the spring rate a lot stiffer. This means that for a given amount of cornering force, the suspension compresses less, reducing roll.

Another way is to reduce suspension travel. Say I took that same cornering car and made it so the outside suspenion would only compress an inch. Yes, the ride quality would be low, and so would traction-- but you'd have almost NO body roll at all!

So how could a traction bar reduce travel? BINDING.


So, all that to say this:
The only way a traction bar can have a sway bar effect (in terms of reducing body roll) is if it is limiting suspension travel by binding.


Now there are other forms of sway which a bar like this could conceivably help. Trailer sway can be greatly accentuated by sloppy axle location, and a bar setup like these Lazar bars would do wonders for towing stability. Definitely an "anti-sway" effect.

I hope I've made clear the difference between "anti-roll" and "anti-sway" and how the traction bars can do one, but not the other without compromising suspension travel through binding.

Justin

 

That's exactly what I experience.. bars pushing rearward and springs lifted in the back!
And surprisingly it makes for a better feeling ride, IMO. Definately better cornering!

RJ

 

The "springs lifting" is a form of suspension binding.

Binding isn't always a bad thing. Drag racers often use a form of "binding" due to torque forces to help plant the tires extra hard (lift the chassis).

You're probably giving up a tiny bit of travel, and increasing stress on the springs (as they absorb the binding)-- but they can handle it.

It sounds like it's a compromise you're willing to make. I know *I* would be willing to make that same trade. That last inch or two of travel on these trucks is really for the Baja guys-- most of us will never hit those stops.

jmo

 

PM me please with a price on the long combo bars please...oh why not...price on all the bars that will fit my 2001 Quad Cab short box 4x4.

Thanks

 

.


HOHN, I did a little math and those pipes have the same cross sectional area of steel, or same weight per foot.

You could drive the point about moment of Inertia by stating that a 6'x3"x3" piece of 5/16"wall structural tubing 10.58lb/ft will hold 63K.

Whereas a 6'x4"x4" piece of 3/16"wall structural tubing 9.42lb/ft will hold 64K.

One more point is that the shorter the length, the less important the shape of the steel tubing or pipe and more and more important the total cross sectional area of steel.

At 0-2ft of length, and equal cross sectional areas of steel, a 4"x4" piece of tubing is only 0.6% stronger than a 3"x3" piece of tubing.

What i'm getting at is the shorter the traction bars the less difference size of pipe makes but rather the weight per foot is most important.

I hope that those longer traction bars have a thicker wall or bigger tube, or the shorter ones are way over engineered.

Thats my take on it anyway.

 

They are on both accounts and the long bars are just as over engineered and strong as the short bars.

 

Those bars look nice, but I guess I'm going to be the first to say, tractor links really don't belong on suspensions!

They are probably strong enough, and I know they are cheap so I'm sure that is part of the reason for using them, but they WILL NOT last. They are pretty sloppy brand new, and it's only going to get worse. They will get sloppy enough that the clunking will drive you nuts.... shoot even good heim joints do that after a while.

There is a reason that good quality heim joints are expensive... because they are quality!

 

Well, I *could* have said that, IF I would have had the exact numbers in front of me. My point was just that for the same weight per foot, the larger diameter is stronger.

I'm no engineer-- just a guy that tries to reason things through

 

Ok, no problems, I'm no engineer, just a construction management guy that has to deal with structural steel once in a while so I have numbers on hand.

 

wow....you guys really have some time on your hands huh??? All jokes aside though, I think for the average and even sophisticated individual these bars are the ticket. Cheaper than the competition and just as strong with excellent customer service. After all,isn't customer service what we are all striving for? Just my 2 cents...

 

Sorry for the delayed response, guys - we switched security suite vendors early this week and a lot of office (& computer time) has been tied up with IT garbage.

Thanks for the compliments, Justin!

The bars are available in a variety of colors, and powdercoating is also available as an option; the standard finish is stainless steel powder paint.

Although there are no weak points in the bars (or anything else we manufacture) , the frame brackets feature a sacrificial hardware mounting design that functions as a mechanical overload/early warning of parts breakage in the rest of the driveline behind the tranny. The same line of reasoning where I wish one of the universal joints had failed instead of blowing the spider gears through the rear diff cover of the '98's Dana 70!

Most engineering materials are stronger in tension than compression - concrete is a notable exception to this convention.

Since the Lazar Bars are heim-mounted on each end, the bending moment is a function of the compressive strain only; the "ladder bars" that are rigidly mounted to the axle tubes act as lever arms with significantly higher deflection forces acting upon them. You can balance a super-sized soft drink on the end of a straw, but you couldn't use that straw to lift an order of fries without buckling it.

I don't have any issue with welding on axle tubes, frames, engine blocks & heads - or anything else - since I have 3 decades of experience behind a #11 shield - but many people aren't comfortable with it, so we don't promote it.

I designed the rear heim mounting location as far below the axle tube centerline as possible w/o reducing ground clearance, and the forward mounting location of the front heims on the frame provides more of a parallel link.

While tension and compression loading each present their own benefits and drawbacks, I can't characterize one of their failure modes as more catastrophic than the other based on empirical results or CAD-realm node/cell theory prediction.

The traction bars are easily adjustable for the amount of preload desired, to remove any tolerance stacking and it's associated noise, while varying how hard you hit the rear tires coming out of the hole - if you're into that sort of thing.

Generally speaking, I agree with your assessment of ideal structural cross-sections for tension and compression loading, with the following caveats:
tension-loaded shape performance increases in relation to the surface area/cross-section area ratio (one of the reasons for a cable's strength over a solid bar); and excessive rigidity in compression-loaded structural shapes leads to premature failure (due to the material's low modulus of elasticity to yield-strength ratio).

You may have fallen victim to Semantics!
At the risk of the same fate, I'd say that conventional anti-roll (or is that "sway"? ) have their torque arms forced in opposite directions by cornering forces, and traction bars do indeed perform the function of an anti-sway (or is that "roll" ), albeit by increasing the effective spring rate, as you've already concluded.

Heim-less traction bars will promote suspension binding, although the relatively low-durometer bushings those low-cost pieces come with allow enough slop for users to claim sufficient articulation for their needs.
That's why we use heim joints on both ends of the bars!

That's for sure!
We've abusively overloaded the service trucks from time to time and the bumpstops have never been within a long inch of the frame.

Don't forget that structural shapes as well as sizes should be tailored to the load requirements - that's why we design trailer decks with tall & narrow structural pipe for a high strength-weight ratio.

When we first unveiled the lazarsmith traction bars, the basic reaction was Wow - overkill over-the-top ... now there's hope that they're over-engineered?

These aren't tractor links that feel like you could pull the ball out of the end with your bare hands, and at $40/pop (am I allowed to say that? ) they don't seem very cheap to me!
They don't have slop even after 10's of K's of miles, and they don't clunk at all when properly adjusted.

These traction bars are max bang for your buck!

I'd love to fabricate a 4-link rear suspension for our trucks that would have zero unwanted spring deflection, maximum articulation, large payload capacity and a silky smooth ride, but I don't think anyone would want to pay for it!

I only make time to design & build parts for the Dodge CTD Rams that the average person can afford & appreciate.

p.s. not including the "specialty" items I add just because I can!