Ed Huntress wrote:

Because the tubes could be of larger diameter and *also* have thicker walls,
for the same weight -- thus producing a higher value "r."

I picked 2" as an example but the same comparison applies to any OD
until the walls become so thin that other factors become involved.

In fact, that's how the Bobsy was designed, with aluminum tube space frames,
back in the '60s.

That doesn't neccessarily make it right.

Ted