Opting for thicker wall tube in the hopes of gaining greater strength is rarely a worthwhile solution. Usually, the major rise seen is in the weight of the structure rather than the strength of it.

If space and components permit, a better solution is to go up at least one tube size while retaining the original wall thickness.

For example, if you've built some A-arms from say, Ø25.4mm x 2.1mm wall [1.0" x .083"] tube and discover to your horror that the lower arms are bending like bananas, your first thought might be to increase the wall thickness to, say, 3mm [.120"] in an attempt to rectify the problem.

Let's compare some tube

Your initial choice of tube for the A-arms was Ø25.4mm x 2.1mm wall [1.0" x .083"] which has a weight per foot of 0.37kg [13.01 ozs] and its moment of inertia is .025.

Your gut reaction was to remake the A-arms from  Ø25.4mm x 3.0mm wall [1.0" x .120"] which has a weight per foot of 0.51kg [lb1 2.08 ozs] and its moment of inertia is .033. So, that's an increase in weight of 40% (0.15kg [5.11 ozs]) for a 30% increase in strength.

Let's see if we can better it by going up just one tube size while retaining the original wall thickness.

So what we find is that Ø28.58mm x 2.1mm wall [1.125" x .083"] tube has a weight per foot of 0.42kg [14.8 ozs] and its moment of inertia is .037.
WOW! The weight has only increased  by 13% (0.09kg [3.17 ozs]), but the strength has soared by 48%. Way to go!

While not capable of analysing the dynamics of welded tubular structures, you can use the calculator below to compare other tube sizes.

The main reason this calculator uses imperial measurements as opposed to metric, is because the majority of the "good" tube (DOM, CDW, 4130 etc.) is still produced/imported in imperial sizes.

To calculate a tube's comparative strength, enter the tube OD and wall thickness (in decimal inches) into the boxes below and click on the "Calculate" button.
Use the "Reset" button to enter a new set of figures.