Vehicle Side Bearings: Function, Performance
and Maintenance (Part 1 of 2) By Gary Wolf • April 04,
2005
Side Bearings serve as support elements on
the truck bolster and are located to the side of the centerplate.
The function
of the side bearing is to support the underside of the car body
bolster in the event the car leans to one side or the other.
When a car operates around a curve on superelevated track, the
car body can lean to the outside of the curve if the car is traveling
over balance speed; or it can lean to the inside of the curve
if the car is traveling under balance speed. The car body, which
is normally supported entirely by the 14- or 16-inch body centerplate,
can tip or roll up on the outer edge of the body centerplate.
If there were no additional means of support, the car body, in
extreme cases, could tip on its side. The side bearing prevents
an excessive amount of tipping by providing additional support
at a location approximately 24 inches from the car center pin.
Figure 1 shows a typical application and location of the side
bearings on a truck bolster.
The modern side bearing consists of a hardened 3-inch steel roller
placed into a steel cage, or box-like device. A single roller
is used in 70-ton cars, two rollers are used in 100-ton cars.
The steel cage is typically bolted to the truck bolster with
two fasteners. There is adequate longitudinal clearance in the
cage to allow the roller to move back and forth. Allowing the
side bearing roller to move back and forth facilitates turning
of the truck bolster on the car body during curving. A hardened
flat steel plate is attached above the roller to the car body
bolster. The roller rubs and bears against this flat steel plate.
There is a gap on approximately 1/4-inch between the roller and
the body wear plate (see Figure 2).
SEPTEMBER 2004 "Truck Warp:
Causes and Cures (Part 1 of 2)" READ
ARTICLEOCTOBER 2004 "Truck Warp:
Causes and Cures (Part 2 of 2)" READ
ARTICLEAUGUST 2004 "Improving Truck
Designs to Reduce Forces Transmitted to Track" READ
ARTICLE
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Side Bearings serve as support elements
The modern side bearing consists of a hardened 3-inch steel roller
placed into a steel cage, or box-like device. A single roller
is used in 70-ton cars, two rollers are used in 100-ton cars.
The steel cage is typically bolted to the truck bolster with
two fasteners. There is adequate longitudinal clearance in the
cage to allow the roller to move back and forth. Allowing the
side bearing roller to move back and forth facilitates turning
of the truck bolster on the car body during curving. A hardened
flat steel plate is attached above the roller to the car body
bolster. The roller rubs and bears against this flat steel plate.
There is a gap on approximately 1/4-inch between the roller and
the body wear plate (see Figure 2). 
