I just don't see the huge difference in price between DOM and ERW.. Maybe its because I buy so much tubing, but the price diff for me is 10-15% at low quantities(<200ft). In reality DOM costs me less because I buy it 1000+ ft at a time.. A low quantity of ERW would cost more per foot. There is no ERW in my shop, I don't use it.
DOM is stronger, the cold working of the tube adds a lot of toughness, I don't have my strength tables here in front of me, but I know the strength difference is significant.
One of the main reasons that SCCA, NASA and others have gone to DOM only is its accuracy and concentricness. Oft times when you measure the thickness of ERW you get variations that will give you a measurement under the required thickness, oops, fail. Most DOM is spot on (within 2 thousandths) while ERW usually varies from .111 to .131 on a .120 wall thickness tube.
Yes, cage design and weld quality are more important, and we are cracking down on crappy, lumpy, cold welds.
DOM has become the standard in road racing and We (Lemons) recommend it strongly in our rules.. Please use it if you can.
I just called around NoCal as a consumer, not giving my business name and asking for 100ft of 1.5 X .120 ERW and 1.5 x .120 DOM.. the price difference varied between $.65 to $1.23 per foot.. An average car with Minimum Lemons cage will use 60ish feet, a car with added bars will use up to 100ish feet. So I see the price difference as about $40 to $110... Not that bad of a hit to use the right stuff.
-John
Gosh, my business card says 'Tech Tyrant'