A Radial steering truck is a type of bogie used on locomotives. On railroad equipment, "trucks" or "bogies" are the wheel assemblies that the train rides the rails on. Trucks are found on almost all train equipment with the exception of some steam locomotives (e.g. a 0-6-0). On diesel locomotives, unlike freight or passenger cars, the trucks are powered, with an electric motor mounted on the truck connected to the driving wheels through spur gears with different gear ratios being appropriate for freight or passenger service.
On locomotives, these trucks may have two, three or possibly four axles, making the truck quite long. Such a long truck, particularly the three and four axle variants, makes it difficult for the wheels to go around curves. To solve this problem, Electro-Motive Diesel (EMD) designed the Radial Steering Truck. This design allows the wheels to pivot around the center of the curve somewhat, allowing less wear on the wheel flanges and rails.
Claims are made of an increased factor of adhesion with radial steering trucks.
While sound in theory, the design has produced mixed results in practice. Increased flange wear and decreased ride quality have been observed and some feel radial steering trucks are the answer to a question that wasn't asked. Many locomotives have had the active steering disabled through removal of the main steering link.
Four axle trucks are no longer manufactured domestically, but are still widely used.