4mm Wagon Suspension Systems

Why is it desirable to have some sort of springing?  Even if your track is perfectly flat, some flexibility between the axles of a wagon, bogie or locomotive is desirable.  The wheels of an axle are coned so that if the axle tends to one side it rides up onto a larger diameter, whilst the other side rides down onto a smaller diameter.  This means that so long as the wheels are fixed to the axle (unlike the old Triang system) and rotate at the same speed, then the wheel that has ridden up will tend to run ahead of the other one and the wheelset will turn so as to bring it back to the centre of the track.  On straight track this results in simple self centering of the axle.  On curved track, the same action will occur except that the axle will stabilize off centre so that it follows a curve to match that of the track.  However to do this the axles of a wagon must be free to lift and drop relative to one another.