4130 vs Mild Steel 

king0cans how old are you, 30??

Defender Fabrication Yeah I noticed that too. You're right the stiffness of all steel is about the same. In practice the mild steel tube will need to be thicker wall to achieve the same strength so will actually be a stiffer tube.

Stiffness in the tubing is NOT the same as stiffness in the chassis structure. The 4130 tube chassis when designed correctly, will have higher overall stiffness for a given weight than mild steel. You can't pick out a sectional stiffness of a tube and make a general statement about chassis stiffness. The fact 4130 steel allow a designed to build a light chassis with the required stiffness is why it is used. Another fact is this 4130 steel is certified to mil-std means you know exactly how the 4130 steel behaves. The mechanical property of mild steel is all over the place.

2Phast4Rocket Agree, that's why you have all those triangulation pieces and trusses and gussets and things everywhere. 4130 is always going to be a superior material whenever weight is a factor (and cost less so!)

@@2Phast4Rocket 100 % wrong. Not sure where you got your mechanical engineering degree but where I received mine this makes no sense. Youngs modulus does not change when incorporated into a built up section. The stiffness is for all practical purposes the same for the two. What is not the same is the amount of stress it can take until it has permanent deformation. Also, mechanical properties of low carbon steel are not all over the map. At least not the tube made in the USA. It is also made to standards.

@@lastditch5968 You really need to read my post more carefully before responding. I was not referring to Young's modulus at all. The material Young's modulus is very different to the structural stiffness from structural design where structural stiffness is measured in natural frequencies and structural deflections based on the specific loadings and constraints.

on the question of weight, both materials have nearly identical specific weight, meaning for the same volume of material they would have a negligible weight difference. i.e. a 3' section of 1.5"OD 0.095" wall of both CM and Mild will weigh the same. What is important to look at is the strength density or in other words, a 1' section of 1.5"OD 1.34" wall of Mild Steell (1.993lb/ft) has somewhat equivalent strength as a 1' section of 1.5"OD 0.065" wall CM(0.996lb/ft). So it's not the weight of the material that makes the difference its the strength, since CM is so much stronger than Mild you have to use much less of it.

@@rudyrayaaw5138 The strength only comes into play when the tube is subjected to bending loads or pure tensile loads. In a properly triangulated frame, tubes will buckle under compression long before they would fail in tension. And the buckling strength of mild steel and 4130 is identical, since they have the same modulus of elasticity. But few car frames are properly triangulated frames, unlike aircraft structures.

I used an aircraft metal supplier. They had the cheaper prices for bulk buys

Blake Matney you tree'd me. I know top fuel is reluctant to change materials as well as NASCAR but I'd love to hear Tims opinion on the future of pro mod and TS regarding construction with docol.

To continue with Docol R8, it has a welded seam instead of being a dom tube. What are your thoughts on that?

Docol R8 is an accepted material in substitution for 4130 in the SFI series of chassis.

@@mikegrady4 Dom has a welded seam its just not as noticeable.

@@Tsalinger, true, the first stages of manufacturing are identical to ones used to make ERW tube except in the finishing stages the entire flash weld is removed and the tube is cold drawn over a mandrel. The cold drawn process essentially makes the tube more symmetrical with regards to its consistency of strength and its resistance to bending. That is a substantial difference.....especially since we typically bend the tubing. This can be a huge deal depending on where the weld is, relative to the bend, when using typical ERW tubing.

Just about everything made in America has a Mil-spec # and there are thousands of Mil-spec

CM is superior in almost all categories except price www.makeitfrom.com/compare/SAE-AISI-1020-S20C-G10200-Carbon-Steel/SAE-AISI-4130-SCM430-G41300-Cr-Mo-Steel

Right there with ya, brother..also, CM has to be tigged, while mild steel can be Mig welded..cheaper, easier, and more forgiving welding process..particularly for a weekend warrior building their own junk rather than doing it for a living. I don't have the skills or the equipment to build a CM chassis, but I can put together a safe mild steel car.

i can understand Mr McAmis insisting on 4130 because he's at the absolute top level of competition with the corresponding budgets, plus the regs require it. however, not to take away anything stated above, every book i've read about road racing chassis design and fab (especially Costin) state mild steel is perfectly fine. i'm not a pro nor do i plan on wheel-to-wheel racing, and i'm certainly not in an elite category so i don't need to have the absolutely lightest chassis. as such, i have about 200 ft of 1.5" OD x 0.093 seamless - yes, seamless - DOM mild steel in the shop now waiting for me to clear the decks and start my build. plus, i worked a couple years in a high end custom bicycle framebuilding shop, and 4130 does lose some of its temper when TIG welded in the heat affected zone, which renders it the same as mild steel.

chromoly is stronger in a thinner wall thickness, fractures easier than mild steel. Biggest pro for chromoly for me is that it doesn't rust! Especially when you are taking your time fabricating something with mild steel, it starts rusting with just the moisture in my garage

Peter Armour That’s damn true, I’m a sandblaster by trade but also do Powdercoating and a little fab here and there and I’ll be the first to tell you mild steel rust real quick. I can see where chromoly would have its place. Thanks for the response man I appreciate it

Lighter is gooder, Racing 101,

No need, These aren't open root welds

I didnt see that untill I read your comment and went back to the vid............ fuck me... thats some serious overdrive and BOOST...... good catch

That looks like a c rotor to me. If not its a d. Most run them 90-120% over

Depends. But I do agree that military grade is held to a higher standard than it should.

In the real world everyone uses DOM especially if your welding a cage to a sheet metal chassis. Just check a rule book for the class of car your going to run. Not many require CM.

@@Tsalinger I have a 8.5 cert on my drag car. I could have used DOM but chose CM instead.