Quote Originally Posted by driftspin View Post
Hi Paul,

Are you sure about the stiffness you describe above.

As a rule of thump, steel is more rigid by a factor of 3 for a given shape at the same weight.

Box section should be more rigid than tslot profile..

You explain above the tslot alu 13.5kg is more rigid than the steel box at 18kg....
Aluminium is stronger/stiffer than steel for a given weight. By volume steel is stronger, but not necessarily stiffer, as Steel generally has more elasticity than aluminium.

Off course that's a very general observation, as strength will depend on the exact profile/loading/application.