From what I recall all Nextel Cup chassis are Cold Drawn Seamless tubing.
DOM is not
necessarily stronger than ERW (Electric Resistance Welded) for a given alloy. DOM (Drawn Over Mandrel) has a more consistent size and shape so that it has consistent properties in any direction for lack of a better term. DOM still does have a seam that is fused therefore you still have a heat affected zone down the length of the tube. After the tube is formed and welded, it is then pulled over a mandrel to accurately form the shape which provides a more uniform wall thickness, ID, OD. This also does some cold working and can possibly add some strength.
CDS (Cold Drawn Seamless) tubing is formed from a solid carbon steel bar by drawing it over a mandrel to form it's shape. Therefore there is no welded seam. This process also cold works the steel and improves it's mechanical properties.
Chromoly Tube is basically CDS tubing made from 4130 alloy steel. Standard CDS tube is typically 1018 or 1020 carbon steel. The 4130 alloy has greater tensile and yield strength than 1020 while maintaining good ductility. However it does require certain things be done before during and after the welding process to ensure the weld integrity as well as the quality of the base metal in the heat affected zone of the weld.
As said before, Chromoly is not lighter than CDS or DOM. Because it has better mechanical properties, you can typically use less wall thickness for a given tube than CDS or DOM.
I am not a metallurgist or welding engineer, but it is my opinion that you should not attempt to use 4130 unless you are well schooled on the requirements of properly welding this material. I have seen failures that can be attributed to not doing it properly and by people that say gee "I have done it like this for years with no problem". They just got lucky for years. I can't go into the proper procedure because frankly, I don't know it. Meaning there are different methods for different thicknesses, weld processes and weld joint configurations.
Honestly, these same considerations should be taken into account for any structural/safety related weld. I can weld, but when it comes to these types of welds I get a friend and certified professional welder to do it for me. I think it is worth it.
Well, thus ends me running off at the mouth. Don't take this as gospel just me trying to pass on some information I picked up along the way. Sorry for the book. Hope it helps.
