OK, so I am considering selling the heavy and wide TT Zega plus rack setup, and make my own luggage rack just like I did with the LC4. Allows me to make a less wide setup with the weight lower and more forward. Soft luggage for trips, small hard cases for daily use. I would like to keep the rack light. It is used only 10% of the time, and the other 90% of the time it is only dead weight. Keeping it light can be done by using light materials or larger diameter tubing with thinner walls. Now, the most practical materials for building the rack is either steel, stainless steel and aluminium tubing. I don't want stainless; very expensive and fairly hard to come by. Steel is always a good option, but again: obtaining large diameter thin walled steel tubing is not easy also, and steel rusts. And then there is aluminium. Easy to process, easy to obtain tubing in smaller quantities, does not rust, not as expensive as stainless. But, less stiff and strong (especially as-welded), so larger diameter tubing and larger wall thicknesses required. Questions: 1) Is there a good reason why aluminium is seldom used as luggage-rack material, apart form the 'middle of nowhere repairability problem'? 2) Say I have a construction made of steel pipe with diameter X and wall thickess Y. Now, if I want to make the same construction with the same stiffness using aluminium tubing with wall thickness 1.5 * Y and I keep the dimensions of the construction the same except for tube diameter, how much larger would I have to chose the the diameter of the tubing? I don't think alloy choices affect the outcome much, but if you need numbers: regular steel vs extruded 606x-T4 tubing. Steel pipe diameter 16mm x 2mm wall thickness (approx 5/8" x 0.08"), aluminium 3mm wall thickness.