In 1814 English engineer George Stephenson built the first steam locomotive for operation on iron rails. It was unique from previous self-powered steam vehicles in this respect: For traction it used flanged steel wheels for adhesion to steel rails.
One hundred ninety years ago flanged steel wheels became the standard for worldwide railroading.
Trackmobile subscribes to that standard for the same reasons as the railroads:
Steel wheels are more durable than rubber or polyurethane
The coefficient of friction for steel on steel is more consistent over a range of conditions (snow, ice, rain, contamination) than the coefficient for rubber or polyurethane on steel
Steel wheels have far less rolling resistance than rubber or polyurethane tires
Steel wheels are unaffected by raised frogs, switch points, gaps between rails and by material packed into grade crossings
Steel wheels maintain point contact with the rail while rubber pneumatic tires deform over the 2 inch (51mm) width of the railhead
Steel wheels are puncture-proof while rubber tires must be either solid rubber or foam-filled to avoid puncture
The point about deformation is important. Tires are designed to spread their loads over the entire width of the tread positioned on a flat driving surface. When a pneumatic rubber tire is placed on a railhead, one fourth of the vehicle weight plus some weight transferred from trailing loads is concentrated on only 2 inches (51mm) of the tread width. The photo above shows how a tire deforms under a 42,000 pound (19,000kg) vehicle because 75% of the tread width of a typical industrial tire is unsupported. The deformation imposes loads on tire sidewalls, cords and beads that are not experienced in normal tire applications.
Additionally, while rubber has good characteristics under compressive loads, it does not have good shear resistance. In a rail application, the tires are subjected to compression of the vehicle weight, and simultaneously to shear forces when torque is applied to rotate the tire. Under shear plus compression forces plus friction between the tire and the steel rail, the tread rubber heats rapidly to the point the rubber breaks down.
For these reasons, steel wheels have always been chosen over rubber in serious railroading.