[ErikB]

I found this thread while searching for some square vs. round info.
I added some numbers for square tube and some .188" wall stuff, along with weights per foot.

Square tube weights from here:
http://www.jimssupply.com/square%20rec_tubing.htm
Round tube weight formula here:
http://www.engineeringtoolbox.com/st...hts-d_774.html
Found MOI calcs for round and square tube here:
http://mnhpva.org/tech/frame_tubes.html
That page has a great explanation (Realsquash summed it up pretty well). I just made a little excel sheet to do the calcs.




OD_ / ID_ = ....MOI........ Weight
.......... round square ,round square
1.5 /.120 = .125 , .212 , 1.77 , 2.25
1.5 /.188 = .170 , .289 , 2.63 , 3.35
1.5 /.250 = .199 , .339 , 3.34 , 4.11
1.5 /.375 = .233 , .... , 4.51
1.5 /.500 = .245 , .... , 5.34

1.75/.120 = .205 , .348 , 2.09
1.75/.188 = .285 , .484 , 3.14
1.75/.250 = .341 , ....., 4.01
1.75/.375 = .411 , .... , 5.51
1.75/.500 = .445 , .... , 6.68

2.0 /.120 = .314 , .534 , 2.41 , 3.05
2.0 /.188 = .444 , .754 , 3.64 , 4.32
2.0 /.250 = .537 , .911 , 4.67 , 5.41
2.0 /.375 = .666 , .... , 6.51
2.0 /.500 = .736 , .... , 8.01

2.25/.120 = .457 , .... , 2.73
2.25/.250 = .798 , .... , 5.34
2.25/.375 =1.01 , ..... , 7.51
2.25/.500 =1.138 , .... , 9.35

2.5 /.120 = .637 , .... , 3.05
2.5 /.250 =1.132 , .... , 6.01
2.5 /.375 =1.457 , .... , 8.51
2.5 /.500 =1.669 , .... ,10.68

Nuts to think that .250 wall 2.0 is 25% stronger than a .500 wall 1.75 tube. Crazy.

Its actually about 20% stronger by my calcs... and 30% lighter.

Thinking out loud...

2 x .188 square would be about 35% lighter and 70% stronger than 1.75 x .5 round.

2 x .120 square has nearly the same MOI as the 2 x 250 round, and is 35% lighter still (or 25% stronger and less than half the weight of the 1.75 x .5 round). Unfortunately, it would probably dent too easily.

Seems like 2 x .188 square would make some really strong and relatively light links. Similar to 2 x .500 round, but almost half the weight!