Control arm design question

WesRJ86

WesRJ86

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I understand it's generally best to just buy adjustable control arms, that's not what this thread is meant to discuss. I'm curious why companies and the few who do build their own seem to use DOM? Would using solid round stock, steel or aluminum, that has been drilled and tapped in the ends be the same? I understand the DOM would be lighter, is that the only advantage? I'm new to trying to understand the design and material choices for suspensions so excuse me if the answer is obvious.
 
Core 4x4 and others use DOM. Different wall thicknesses. Usually the lowers use a heavier wall tube.

Saavy uses solid aluminum.

Lots of choices.

I'm saving up for the Saavys.

-Mac
 
Other companies use solid stock, RockKrawler is one. I'm no metallurgist, but my understanding is that DOM has almost the same resistance to bending as solid (solid is still stronger) at a fraction of the weight. I've used both. The solid stock I have is usally from shit RockKrawler lifts I've removed.
:D
 
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I don't know current prices but at some point (dia + wall) tubing is also cheaper than solid. It's a more efficient use of material.
 
pcoplin said:
my understanding is that DOM has almost the same resistance to bending as solid (solid is still stronger) at a fraction of the weight.
:D
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You can't say that without providing spec's since that is a shit rule of thumb. You can however, find a tube strength calculator and use that to define various strength ratings of common tube and solid bar diameters as a comparison. Rogue has one that is pretty easy to use.
Keep all the parameters the same but change material and wall thickness to get the safety factor the same for comparison or keep the load the same and watch the change in the safety factor.
This is 2" x .120 wall in normal DOM. If you change only the material, you can see the change in safety factor.
1678541227704.png


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Or, you can change the load to get the safety factor back to anything just slightly over 1.0 to see the load comparison. This is normal DOM compared to 4130

1678541544262.png


To compare your rule of thumb, you can pick one material and diameter along with a common wall thickness and then do solid in the same diameter and material to see what the actual difference in strength is. Start with 2" OD x .250 wall DOM.
1678541904887.png


Solid is roughly 32% more resistant to bending. But it comes with a big penalty in weight. 2" .250 wall is 4.6 lbs per foot, 2" solid is 10.7 so more than double.
1678542076675.png
 
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@mrblaine Where's solid aluminum on that calculator in terms of safety factor? And what's the formula for that number or at least does a .4 change in safety factor mean it's 40 percent less likely to break under load?

Found the calculator on RogueFab.com. looks like 1.309 for 2" 6061.

Safety Factor is based on your load...so 4000 x 1.309 = 5236 is theoretically where it would fail.

-Mac
 
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WesRJ86 said:
I understand it's generally best to just buy adjustable control arms, that's not what this thread is meant to discuss. I'm curious why companies and the few who do build their own seem to use DOM? Would using solid round stock, steel or aluminum, that has been drilled and tapped in the ends be the same? I understand the DOM would be lighter, is that the only advantage? I'm new to trying to understand the design and material choices for suspensions so excuse me if the answer is obvious.
Click to expand...

There are a lot of variables you can pick from to build something that fits within a particular philosophy you are adhering to.
How much strength do you need?
Do you care about weight?
Does ease of manufacturing matter?
Are you trying to balance cost against ease of production?

Pick an aluminum arm for example. Do you want to drive the cost up, way up by using tube with right ID so you can just tap it without drilling? Or does the cost of drilling solid make enough sense that you can put more money in your pocket with that choice?

How many are you going to do? The more you do, the more cost effective you can get with special requirements.

The answer isn't obvious without defining the end goal.
 
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Thanks guys, this answers my questions. It's not that a certain material has to be used, it's just weighing the pros and cons of any chosen material. Thanks for the calculator link @mrblaine
 
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Just remember DOM tubing is not made from any specific alloy – it can be used with mild steel, chromoly or another alloy, such as SAE 1020 or 1026 steel. So if you’re planing to order metal to build your own parts it’s best to understand your designs strength requirements and which material best meets those needs.
 
Havasu said:
Just remember DOM tubing is not made from any specific alloy – it can be used with mild steel, chromoly or another alloy, such as SAE 1020 or 1026 steel. So if you’re planing to order metal to build your own parts it’s best to understand your designs strength requirements and which material best meets those needs.
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Easier way is to have them understand that DOM is a process. It stands for Drawn Over Mandrel to mow down the weld seam at the bore and cold work the tube to work harden it and bring up the stiffness some. It will be inherently more resistant to bending in most alloys when compared to the normal non DOM versions. That and I don't know if you can even get some alloys in other than DOM like the 4xxxx series stuff.
 
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The decisions for what to use for the body of the control arms are pretty much what I thought so I understand that part. Now for better understanding the joint part. I've read a fair amount about the different joints and understand why the Johnny Joint is a usual favorite. Why does no one offer a solid body adjustable arm with a OEM joint? Is it simply because you get more articulation from the aftermarket joints and that's what people are wanting? Or does the OEM joint require a body that can flex with it like the factory arms?
 
WesRJ86 said:
The decisions for what to use for the body of the control arms are pretty much what I thought so I understand that part. Now for better understanding the joint part. I've read a fair amount about the different joints and understand why the Johnny Joint is a usual favorite. Why does no one offer a solid body adjustable arm with a OEM joint? Is it simply because you get more articulation from the aftermarket joints and that's what people are wanting? Or does the OEM joint require a body that can flex with it like the factory arms?
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The Clevite style bushings tend to usually wear faster as you increase the amount of articulation. If you don't mind swapping them out from time to time, no reason to avoid them at all. Cheap, effective, easy to replace.
 
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The cost of dm vs aluminum isn’t that much, especially if you’re not looking for polished and engraved arms. Especially after you start replacing bent arms.
 
WesRJ86 said:
... Why does no one offer a solid body adjustable arm with a OEM joint? Is it simply because you get more articulation from the aftermarket joints and that's what people are wanting? Or does the OEM joint require a body that can flex with it like the factory arms?
Click to expand...

The OEM U-channel arms flex a little. Some companies make similar rubber joints with solid arms, but they tend to rip off your frame mounts because they're too stiff. Flexy arms with stiff joints is fine. Stiff arms with flexy joints is fine. But offroad where you're articulating your axles, a stiff arm with a stiff joint will twist against the frame mounts pretty hard.
 
OldBuzzard said:
The OEM U-channel arms flex a little. Some companies make similar rubber joints with solid arms, but they tend to rip off your frame mounts because they're too stiff. Flexy arms with stiff joints is fine. Stiff arms with flexy joints is fine. But offroad where you're articulating your axles, a stiff arm with a stiff joint will twist against the frame mounts pretty hard.
Click to expand...

This answers what I was curious about. Thanks 👍
 
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