Quote:
Originally Posted by Chronos
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And to the torque question, doesn't that also depend on how far out from the center the piston rods connect, too? It seems to me that, for any given piston rate, the speed would be determined by the ratio of those two radii.

You're right about the ratios. But the stroke of the piston in the cylinder is equal to 2x the radius where the piston rod connects to the wheel.
So the optimization problem trades off your "gear" ratio versus top speed versus piston stroke. Ideal bore vs. stroke ratios depend on intended cycle rate, metallurgy, and the steam's expansion ratio which in turn is driven by the boiler output pressure.