Conical Shape
Most wheels have a conical shape of about 1 in 20. The conical shape has the effect of steering the wheelset around curves, so that the flanges rarely come into play. The rails generally slant in at the same rate as the wheel conicity. As the wheels approach a curve, they will tend to follow a straighter path. This causes the wheelset to shift sideways on the track so that the effective diameter of the outer wheels is greater than that of the inner ones. Since the wheels are joined rigidly by the axle, the outer wheels will travel further, causing the train to naturally follow the curve.
For more information see Hunting oscillation.
For its first hundred years, Queensland Railways used cylindrical wheels and vertical rails.
Read more about this topic: Wheelset (rail Transport)
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—Percy Bysshe Shelley (1792–1822)