> Normal railways increase the track gauge slightly in curves (because most train cars don't use differentials) Actually gauge widening in curves is to some ex

> Normal railways increase the track gauge slightly in curves (because most train cars don't use differentials) Actually gauge widening in curves is to some extent probably more a remnant of steam locomotives with their comparatively ginormous wheelbases. Based on current knowledge, a slight gauge widening on straight track and a slight gauge tightening on tight curves might actually be more beneficial – while trains don't have differentials, they normally (BART and some streetcar systems excepted) use conical wheels, which can self-steer themselves around curves down to a certain radius. That radius is somewhere in the range of a few hundred metres, but its exact value depends on the equivalent conicity of the combination of wheel and rail profiles. A higher equivalent conicity reduces the minimum radius down to which self-steering remains effective, while a lower conicity reduces hunting and increases stability at high speeds on straight track. Simultaneously, given a nominal track gauge, a slight increase in the track gauge reduces the equivalent conicity, while a decrease of the track gauge noticeably increases equivalent conicity.