Steam Locomotive Driver Wheel Types

As with any component of a steam locomotive, the design of the driving wheels changed over the years because of advancements in technology. Obviously, the main purpose of the driving wheels of a steam locomotive is to support the weight of the locomotive and transfer linear force from the pistons into rotational force applied to the rails. However, there are many other important aspects of steam locomotive driving wheels that may not be immediately obvious. For example:

• The drivers must include counterbalancing to offset the weight of the side rods.

• The diameter of the drivers affect the locomotives top speed and pulling ability. The driver diameter is used in the equation for tractive effort.

• The drivers are made of a "wheel" and a "tire". The inner wheel was cast out of steel and the outer tire wears out and must be replaced periodically.

• Most drivers have flanges. Some drivers, called "blind" drivers do not. Blind drivers may be used on locomotives with very long, rigid wheelbases.

• A driver experiences tremendous amounts of both torsional and lateral force. If a driver developed cracks, it was usually the main driver to which the piston rods were attached.

Pretty much from the beginning of steam locomotives, the drivers were cast with solid spokes connecting the inner hub to the outer rim. A "tire" of stronger steel was heated and press-fitted onto the outer rim of the wheel.

Toward the end of steam, newer technologies were used to construct the inner portion of the driver wheels. The main reasons for the change in technology were to strengthen the driver and to provide better counterbalancing of the main rods. Both of these issues were addressed using "disc drivers" instead of spoked drivers. There were four types of disc driving wheels for steam locomotives. Each was made by a different company and each varied slightly from the others in their appearance.

The four types were:

• Boxpok Disc Drivers

  • Manufactured by General Steel Castings of Granite City, IL

  • Patent numbers US1960039 and US2042160

• Scullin Disc Drivers

  • Manufactured by Scullin Steel of St. Louis, MO

  • Patent number US2177693

• Baldwin Disc Drivers

  • Manufactured by Baldwin of Eddystone, PA

  • Patent numbers US2065217 and US2065217

• Universal Disc Drivers

  • Manufactured by LFM (Locomotive Furnished Metals)