Chrome moly tube question

[Psychographic]

I'm debating between buying a trike or building a trike from a Schwinn 10 speed bike. I bought a set of Jr.dragster rear wheels and am thinking of using lawn tractor tires on them. The hubs for the wheels have a 1 1/4" keyway/clamp setup. I can buy a 5/8" freewheel adapter, and 5/8" x 1 1/4" bearings for the "free" wheel. I would need to have a bushing made for the drive wheel.

As the tires will add about 20-25 lbs., I would like to save as much weight as possible. I thought rather than use a solid axle, i would go with Chrome moly. My question is, what wall thickness should I go with?

 

[RustyGold]

This is actually a case where chromoly doesn't have any real benefit over any other steel. All steels are the same weight and roughly the same shear modulus.

You may be able to get away with tubing over solid, as it may be that solid axles are used just because tubing is expensive...but, the type of steel isn't really important (advantages of chromoly over other steels would be in resistance to bending and thread strength).