Which Company makes "best" replica?

[RICK LAKE]

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.

[ddcobra]

You can't compare a 2 rail chassis to a bird cage style like Kikham,CSX,and D&D.
Don,

[Silverback51]

Originally Posted by RICK LAKE

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.

Just so you don't think I'm ignoring you, I will answer your questions when I get home after work.

[Silverback51]

Originally Posted by RICK LAKE

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.

The strong point of a round tube in torsion is that the stress value is the same along it's outer most surface. That is why we have round drivelines, axles, half shafts, etc.. With a square, rectangular, or other shape of structural material the stresses will be concentrated at the outermost fibers where the shape is changing.

Most of the strength of a round shaft is at it's most outer surface. That is why drivelines are always hollow. The closer you get the center, the less strengh is gained by the material in the center. Why are axles solid? Generally because there is less packaging room for a large diameter hollow shaft.

Here is a link to the formula for a round shaft. The formula changes for different structural shapes.

http://www.instron.us/wa/resourcecen...rm.aspx?ID=173

Needless to say, the design of a frame is very complex. And the most efficient design will be a combination of different structural shapes that are choosen to satisfy the stress loads that it's being subjected to.

Take a look at the NASCAR frames. As you pointed out they consist of rectangular main rails and the rest of the frame is mostly different sizes of round tubes.

Now take a look at a top fuel dragster. It's all small diameter round tubing. Different requirements dictate different material shapes and designs. The dragster is a truss design that also allows a great deal of flex in one direction to allow maximum weight transfer for straight line traction. The NASCAR frame is designed with different requirements, so that design is completely different.

Hope that answers your questions.