4130 Chromoly or ( Chromium Molybdenum ) has a 0.30% carbon content... thus you will have a higher tentancy for stress cracking or metal fatigue... Chromoly still is considered technically a "low carbon alloy steel." But 1020 steel ( Mild Steel ) is also a "low carbon steel" but it has a content that is 0.20%. The carbon makes the metal easier to weld, but the more carbon content makes it more brittle and thus lower the tensile strength of the metal. However, these metals both have a very high tensile strength.

There are several other factors that cause cracking and twisting and metal fatigue but that is a whole other post...

Every national recognized sactioning body recommends GTAW ( Gas Tungsten Arc Welding or better known as TIG ) on a Chromoly ( CM ) cage...

I.E. The NHRA rule book states in Section 16 (General Regulations), Sub-section 4:11 (Roll Cage), second sentence, "All 4130 chromoly tube welding must be done by approved TIG process; mild steel tube welding must be approved MIG wire feed or TIG process".

If you plan on actually using the cage... i.e. reducing torque/flex on the frame and body of the vehicle for a long period of time and don't plan to replace or fix it, go with MS (mild steel) the only way you actually save weight with CM is that you can use it in a thinner gauge. It actually weighs the same if it was the same thickness as the MS. TIG welding process has to be used with CM and . But it does make a slightly better weld. Due to the ability to have a greater tensile strength rod. However, that being said, welding with TIG requires greater skill and knowledge of metals. Which is why it normally cost more to get done properly. ( THIS IS AN AREA YOU DO NOT WANT TO CUT CORNERS ON ) And why would you want to... if it is done improperly you will not be happy with yourself. I know I would not want to trust my potential life on saving a few bucks...

MS can be welded a few ways, but mainly it can be welded in GMAW ( Gas Metal Arc Welding or better known as MIG ) which is cheaper.

Bottom line, if you are racing it 100% of the time, it is worth the cost and weight savings for Chromoly...

Otherwise save your pennies for ponies...

Hope this post helps everyone in the Ford community.


Sorry for the long post just wanted to make sure I was clear on everything and did not offend anyone.. Hope I was clear, but any more questions ask away... and I will try to answer them as best as I can... I am by no means an expert so, I may be off on somethings.. but I believe I am close to 100% on most of this topic...