BtZ42 p.4 - curved spokes

[Monte Davis]

Maybe not just a design style: according to a machinists' blog, curved
spokes were functional in cast-iron flywheels, pulley wheels etc.:

"Spokes shaped like an S, a spiral, a set of semicircular arcs, all do the
same thing - allow some needed compliance so that the spokes or rim don't
fracture when cooling [and shrinking at different rates depending on
thickness, shape, position]... Steel or aluminum have more favorable
stiffness to strength ratios or, perhaps more importantly, more available
plastic yield before fracture, and are therefore not so fussy about
shrinkage. And forged, wrought, or fabricated wheels don't have the same
shrinkage problems that castings do. But back when cast iron was king,
shrinkage fractures were a constant headache."
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