Silverback 51 From all the reading of the old days with cobras, the issue was about frame flex. I think the issue was that round tubing could bend and TWIST easier than rectangle tubing of say 2" by 4". This is my understanding of the issue. Is there a formula about this? IMO this is why Nascar builds there cars with round tubing for the roll cages. It's easier to work with cheaper to buy, lighter the rectangle, and it bends to absorb an accident easier than rectangle and still hold its strength. I believe that the main frame on nascar is still rectangler tubing. I also think that alot of the round tubing built cars have gone to a thicker wall tubing to cut down on the issue we are talking about. Twist and flex.
Rick L.