Exercise your brain

[Toolmaker51]

Individual slats making up barrels are more or less flat and parallel initially. The 'cooper' [barrel-maker] traditionally shaves them into staves.
As staves, ends taper a fair amount in width and somewhat in thickness. The sides also have taper much as the keystone in a masonry arch. The wider side is the barrel exterior.
Assembled, tapers form tight joints retained by iron bands, curvature and tapers resist collapse. The bands are conical form matching angles formed by tapered staves. Staves are notched at at least one end for a barrel 'head' that start the assembly with staves upright. Aside from mating angles, widths anywhere along the individual staves represent their portion of a 360* circle. Mechanically, it produces how an eggshell 'works' by nature. Curved sides direct a lot of weight to a small area when barrel is on it's side, yet form is still resistant to leaks, and far easier to move and handle.
A cylindrical form tall enough to to offer useful capacity would buckle. Why steel drums have circumferential beads formed while being rolled from sheet stock.
Speculation as railroad wheels go, with lazy Sunday morning as an excuse. Surfed answers aren't the challenge; maybe creating the search phrase is, but only with 'auto-suggestions' turned off. Don't let tech do what creative thinking should do first.
Not too familiar with locomotives or railcars; IF they were spoked way back when; that eased casting and weight savings. The 'tire' acted as a barrel band, spokes worked as radial staves, to support the hub; effectively a barrel head. Each is dependant on the other maintaining integrity. Spoked wood wagon wheels as well, including a shrunk on band, called the tire.
I'm anxious to see how responses to Marv's tickler filter in. I'll offer that acuity can [and should] be practiced in vast yet converging manners. One favorite is to visualize and produce clear descriptions in text. The 'what is this tool?' threads offer that in a different manner too. A mechanical thought process looks at features to conceive how they interact, quite like a detective sorting out clues.