40mm x 1.6mm is a little heavier, so I started looking at alternatives.

I used BeamBoy (see image below) to compare the strength (resistance to bending) and came up with this table:

50mm x 25mm RHS seems to be a better option to me ... it's 3.3% lighter than 1.5" SHS of a similar wall thickness, but bends about 30% less.

More significantly for me, it's 7% lighter than 40mm SHS while bending 18% less.

Because SHS/RHS pricing is related to weight, it's cheaper too ... probably saving about $2 ... woo hoo!

The only downsides I can think of are:

- looks ... would rectangular tubing look as nice as the square stuff?
- horizontal bending ... I've assume vertical forces are significantly greater than horizontal forces (the front boom being an exception here ... RHS on it's side?)

BeamBoy calculations for 16 gauge 1.5" SHS: