- Round tubing is stiffer in torsion while square provides a stiffer beam
- Square tubing is easier to fabricate (no ‘fishmouth’ joints) but the tube distorts under load by ‘lozenging’ or ‘panting’.This adds to compliance and may lead to fatigue cracking.
Round tubing is best option, and does not need as much design justification. Harder to manufacture, but will lead to less design and strength issues
- May want to consider square tubing for horizontal frame members to simplify suspension mounting points and makes cutting planar joints easier
- Triangulation/reinforcement in square tubing can greatly improve structural integrity
...