Why train wheels are not of perfect circular cross section?

Question

Why train wheels are not of perfect circular cross section?

Answer 1

To accomodate the allowances while engaging with the rails.

But, it is a perfect circular cross section.

It is not perfect circular cross section, when u take it in longitudinal direction.*

Answer 2

a circumferential cross section is round.  a cross section at 90 degrees is not because if the wheel were perfectly round in this view it would never stay on the rail

Answer 3

It's very simple.  

The wheels are tapered so that the car's trucks can traverse the curves with less flange binding.  This is necessary because the axles do not have a differential as found on vehicles, which allow the wheel on the outside of a curve to rotate faster than the inside wheel, since it has a farther distance to travel.

The taper of the wheels is what accomplishes this on rail cars, but there is still a lot of binding, so most railroads in the US use flange lubricators (the flange is the raised portion on the inside of the wheel to allow it follow the tracks)  which automatically apply grease to the flanges before entering the curve, allowing better tracking and reducing wear on the outside rail.

Answer 4

The axle is in the center of the wheel, but some train wheels, especially the old steam locomotives had a thicker "rim" on one side in order to give the arm connected to the pistons somewhere to connect to the wheel.

At a glance, it looked like the wheel was D shaped, but it is round. Like a D on top of a bigger O

Answer 5

The train's wheels are not just disks, there is a special ledge on each of them. The role of this ledge is very important, it lowers below rail's level and prevents the train from leaving the track. So when you cut the wheel you will find variable cross sections from narrow to widest.