Tubular or boxed?

[Dave M]

I'm looking at LCAs and panhard rods.... is there a difference in performance between the tubular versions and the boxed? The boxed ones seem like they have more heft, but I've never seen tubular ones in person. Anyone know?

[Mark B]

Correct me if I am wrong....


Boxed are stronger..

But tubualar are lighter & seem to be able to hug the chasis better.(When you are talking about SFC's)

[fastTa]

Boxed are significantly stronger due to their being essentially a "twin I-beam".

In a deflection test or a static load test, a cylindrically shaped object will fail long before a rectangularly shaped object will.

I will just depend on how strong you actually need them to be.

Most of the tubular LCA's available to the public are usually strong enough for most street/strip cars.

Boxed LCA's also do not offer the ground clearance that the tubular versions do.

[Jeff_in_Atl]

Check this out from http://www.bmrfabrication.com/faqs.htm

"Which is better, tubular or boxed control arms?"

This has to be our most commonly asked question. We personally feel that either design is equally as strong for the load that the F-body chassis places on them. Because the F-body uses a control arm/torque-arm combination, very little lateral loading is placed on the control arms themselves. The torque-arm takes the lateral loading while the control arms are subjected mainly to a "compression" loading as the rear tries to push them forward into the chassis under acceleration. While an excessive lateral load would dictate the use of stronger(laterally) rectangular tubing, compression loading is much easier to handle and round tubing(of appropriate size)is more than sufficient. Bottom line: if you are an overkill nut and are willing to spend a little more then go with the boxed design, otherwise save a little money and get the tubular arms.

[fastTa]

Originally posted by Jeff 95 Z28
....Because the F-body uses a control arm/torque-arm combination, very little lateral loading is placed on the control arms themselves. The torque-arm takes the lateral loading while the control arms are subjected mainly to a "compression" loading as the rear tries to push them forward into the chassis under acceleration.

Well actually the torque arm's purpose is these two things:

1. Prevent the rear end housing from twisting in an upward direction. "For every action there is an equal and opposite reaction." As the pinion gear tries to "climb" the ring gear the resulting opposite reaction is the rear end housing trying to rotate backwards. The torque arm's purpose is to significantly dampen this effect.

2. As to take advantage of this rotating backwards force, the torque that is being applied to make this happen is tranferred to the frontmost mounting point of the torque arm. This aids in weight transfer during acceleration by "lifting" on the front of the car, and asssists in dampening nose-dive during braking as well.

[Jeff_in_Atl]

Originally posted by fastTA
Well actually the torque arm's purpose is these two things:

1. Prevent the rear end housing from twisting in an upward direction. "For every action there is an equal and opposite reaction." As the pinion gear tries to "climb" the ring gear the resulting opposite reaction is the rear end housing trying to rotate backwards. The torque arm's purpose is to significantly dampen this effect.

2. As to take advantage of this rotating backwards force, the torque that is being applied to make this happen is tranferred to the frontmost mounting point of the torque arm. This aids in weight transfer during acceleration by "lifting" on the front of the car, and asssists in dampening nose-dive during braking as well.

I didn't write that stuff. Copy and paste.

I agree with you and didn't get what they were talking about with the torque arm. When I first read it, my brain was thinking pan hard bar when it wrote torque arm. I think who wrote it is confused of the components name.

I still agree with what it says about the lower control arms though. I think the tubes are more than adequate.

On a side note, my BMR sway bars, STB and SFC came in yesterday. I'm impressed with the quality of workmanship. I got the sway bars and the STB on. Boy they made a HUGE difference. I can't wait till I get the SFC on but it may be a while. I have to put a head gasket on the mini van first. I've never done an overhead cam motor before and this one is a DOHC motor. At least it is a third car and I can take my time. Here is a picture of my car with the SFCs sitting beside it. http://www.claire-marie.net/105_0539.JPG

[Joe 1320]

I have a full BMR rear suspension... the tubular lower control arms are plenty strong for a street car. If you look at how flimsy the stock parts are, no doubt you will see that a tubular LCA is a serious upgrade from OE. The BMR Torque arm is substantially stronger and heavier. You can see that it is meant to take a decent amount of punishment. Actually the original tailshaft mounting of the front torque arm mount is the weakest link. BMR tests this mount down into the low 11s. After that, it is recommended that the mount be moved to a new crossmember brace to take the load off the trans.

I would go with tubular, but with a harder rubber bushing on the chassis end and urethane on the other.

This firms up the mountings, but doesn't transmit as much noise though the rest of the chassis. I have this setup on mine and it is a great combination.

[Injuneer]

Its really impossible to assess the relative strength unless you have ALL the dimensions.... including wall thickness. Generally, a round shape will give you the most efficient use of the material, so round is generally lighter for a given strength. BMR is correct... the loads are 99.9% compressive. The issue is "buckling". Will the relationship of the length to the diameter (slenderness ratio) allow the center of the bar to deflect, and cause failure when it is suddenly subjected to bending stresses. I seriously doubt any of the popular manufacturers have even thought about the real design issues. I suspect they just use "what works".

That said, the Spohn LCA's have demonstrated their ability to propel a vehicle approaching 4,000# to low 9-second 1/4-miles, and pull a low 1.3x 60-ft on a foot brake launch with a 1,000+HP engine. So I think the tubular design, assuming the proper diameter, wall thickness and material specs can handle whatever most of us could throw at it. It "works".

I started with a set of boxed LCA's made by "Just Suspension". They were functional, but extremely heavy. If anyone is into boxed over tubular, they are available for $70.

[UMI Performance]

We carry and manufactur only tubular designs, like Injuneer mentioned given the right diameter, wall thickness, material stats and welding a tubular design can take what ever is thrown at it.

We are very pleased with the strength and tubular design can handle with its weight being minimal. You can also step from a Mild steel tubular design to a lighter stronger chrome moly version if you are willing to speed the few extra dollars. But the mild steel will handle street and strip applications.

[UMI Performance]

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