Wheelset

A wheelset is one axle together with its two wheels and two roller bearings, assembled as a single rigid unit. The two wheels are pressed onto the axle so they cannot turn independently; the whole wheelset rotates together as the car rolls.

Where It Sits

There are normally two wheelsets in each truck, one toward each end. Each wheelset is supported at its outer ends through the roller bearings, which seat in roller bearing adapters that rest in the pedestal jaws of the two sideframes. Through that path the weight of the car body, carried down through the bolster and springs, reaches the rail at the wheel treads and flanges.

What It Does

Because the two wheels are fixed to the same axle, the wheelset both carries load and steers. The tapered tread and the flange of each wheel work against the rail to keep the wheelset tracking through tangent track, curves, turnouts, and frogs. The fixed back-to-back spacing of the wheels is what makes the wheelset gauge correctly to the track.

Wear and Inspection

Wheels wear and are periodically re-trued; axles and bearings are inspected on their own schedules. A wheelset can be condemned for worn or defective wheels, a defective axle, or a bad bearing, and is then removed for repair or remounting. Wheel, axle, and bearing limits are defined in the AAR interchange rules and field manual.