Truck

A truck is the wheeled assembly mounted under each end of a freight car that carries the car body and lets it roll along and steer through the track. For a fuller treatment of how the assembly behaves, see the trucks pillar.

The standard North American freight truck is the three-piece truck. It is built from two sideframes, one truck bolster, and groups of springs that sit in the sideframe spring seats. The bolster floats on the springs and spans between the two sideframes, so the assembly is not a rigid frame; it can flex and warp as the truck negotiates curves.

What Sits On It

Two wheelsets support each truck through their roller bearings. Each bearing seats in a roller bearing adapter, which rests in the sideframe pedestal jaw. The car body bears down on the truck through the center bowl of the bolster, where the body center plate pivots, and is steadied at the outer ends by side bearings. The truck also carries the brake rigging, including the brake beams and brake shoes.

Trucks with three or more axles exist for heavy or specialized loads such as heavy duty flat cars. Wear limits and condemnable conditions for the truck and its parts come from the AAR interchange rules and field manual.