RE: why train wheels are not of a perfectly circular cross section?

Question

RE: why train wheels are not of a perfectly circular cross section?

Answer 1

The wheel treads are tapered so they'll follow the railroad track.

You'd think it was the flange, but it's not.  The flange only comes into play in a sharp curve.

Here's how it works.  The railroad axle is solid, which means the left wheel must turn in absolute lock step with the right wheel.

What happens if the wheels get a little bit "right of center" on the railroad track?   Because of the taper on the wheels, the right wheel is turning on slightly larger diameter than the left wheel.

That makes the axle want to turn left, which brings it back to center.

This automatic correction happens continuously as the train rolls down the track, even in straight track.

Provided the wheels are tapered, of course.  If they're not tapered correctly, the train will "hunt" or waddle down the track, banging flanges as it goes... it's a lousy ride, trussst me on that one!  Bad for the equipment, bad for the track.

Answer 2

I think you are asking why the wheels are tapered, with a larger diameter at the lip side (inside) than the outside. The reason is wear caused by curves. When a solid axle goes around a curve on a flat surface, one wheel has to slip because the length of travel of each wheel is not the same. The wheel on the outer edge has to cover more ground than the inner edge. Think of a horse race. The horse on the rail has less distance to travel than the horses outside. So, when the car goes around a curve. it slides outward because of centripetal force, with the outer wheel on the curve riding on the rail closer to the lip which gives it a larger circumference so with the solid axle, it can travel the further distance. The same applies the the wheel in the inner rail of the curve. With  the car riding out, the inner wheel is pulled out which makes the circumference less. Effectively, the wheels change sizes to match the different distances each has to travel, which reduces the wear. By the way, it is the top of the rail which is curved to reduce the surface contact area of the wheel to as small a contact area as possible to reduce rolling friction, which is why it is that in strongman competitions, one person can pull a fully loaded freight car by himself.

Answer 3

Are you asking why train wheels are not flat across? They need a lip to keep em on the tracks. Also they are bowed to reduce the total area that touches the track to reduce friction.