D.O.M Steel Round Tube Question

detroit or japan....

There is a lot of engineering and such that goes into production vehicles. They manufacture parts and vehicles very cost effective. Ever wonder why things like control arms are so strangly shaped? Why don't they just use tubing like we do when they manufacturer vehicles? Because it is cheaper to stamp the engineered design with less expensive material and get the needed strength out of it.

I was specifically refering to round tubing being used on production vehicles.

Originally posted by tenfrontier



I was specifically refering to round tubing being used on production vehicles.

Thats why you won't find hardly any round tubing on production vehicles.

Anyway, this metal discussion is just another one of those things. Like he said ^^^^ people are going to use whatever they want, have used, or know somebody that used. The facts are in this thread. Chromoly is the strongest, pipe is the weakest. Use pipe if it makes you feel happy, I am going to use what makes me happy.

Here is something else to think about... I am more of a hydro person than bags... Hydraulic cylinders are made from 4130, or in some cases better grade tubing. Why would I hook that to a suspension piece made from mild steel. However, to contradict that statement... the suspension is tied to the stock frame, which is basically mild steel. SO whatever, like I said using the strong stuff makes me happy, so I will pay the couple extra $$ for it.

the advantage of using chromoly is so you can use a thinner wall so you have less weight. just thought i would mention that. more less used in race cars.

tre5- I can appreciate the use of 4130 on all of your suspension related parts and it is true that if you want to get all of the benefits of the chromoly it should be heat-treated. BUT...

and this is a big "but" if any of you have done your material homework you would know this...

For the 99% of the builders out there 4130 is not necessary nor is it practicle. 4130 is a semi-heat treatable material and should be welded with caution. An over heated welment can become brittle adn the general practice of using overly thick material is a problem with 4130 as well. 4130 should be pre-heated before welding on any piece of material thicker than .120. Also, 4130 should not be welded in cold weather without pre-heating the parts to be welded. 4130 is also a lot harder to bend in your everyday benders. To top all of that off, you won't ever find an agreeance as to weather to or not to stress-relieve the weldment and or the type of welding practice to use with 4130. I read somewhere once that if you built a roll-cage out of 4130 and didn't stress-relieve the welds, that the vehicle would break in half over the first serious bump. That is so far off base that it is rediculous!

I'm not saying to not use 4130 and I do thank tre5 for his OPPINION and not "how it must be." But I've played the "4130 thread" game on a different site that should have known better and I finally refused to ever visit the site again. Since then I have talked to people that REALLY know about 4130 and the proper welding practices and am very comfortable with what I have learned from them.

As for my interpretation of "pipe." It is anything that is considered "pipe" in the construction world. Pipe is measured i.d. because the i.d. is more important to something that is going to be used for fluid transfer. Tubing is measured o.d because the o.d. is more important to it's structural properties.

Right. I have welded 4130 with MIG, and never had a problem with the weld, or the area just aft the weld. But, it should be TIG welded in order to control the heat of the weld.

I have heard this discussion too many times to tell people what to do. I would rather tell people what I would do, my opinion. Everyone has there own, and there is no sense starting an internet argument. The only difference between this thread and others is... I have never heard the pipe stuff thrown in, that's a first. Pipe is for fluid or conduit, and (in my opinion, lol) it does NOT belong anywhere else, including vehicles.

I use 4130 on little stuff like control arm, four link bar,and rack in pinion set ups etc.. I would never build a chassis out of it. Its to ridged for that type of use it will start cracking over time. Under impact, as in a crash, a chrome Moly part is much more likely to break rather than bend, as would a mild-steel part.

If your using pipe for just a bit of bracing, or decorative jungle gym work, it's fine, but I would never use it for a 4 link. I've used solid cold rolled, drilled and tapped or DOM Tube.

Originally posted by tacoma101



I would never build a chassis out of it. Its to ridged for that type of use it will start cracking over time. Under impact, as in a crash, a chrome Moly part is much more likely to break rather than bend, as would a mild-steel part.

Don't take this as any type of insult but, that is untrue. If it were true then why are all of the high end BMX dirt-jump bikes built out of 4130? Those bikes are probably the most abused metal structure that a normal human can buy. Chromoly, flexes rather than breaks as compared to mild steel and is used in high abuse and racing applications because it IS more resistant to breakage. If you have experienced cracking rather than bending in your own experiences, then chances are that you did not weld it properly.

This is why 4130 causes such drama. Everyone has an opinion about it, but noone really knows much about it.