Wheel Gauging: Rim

Wheel rim gauging is the inspection of the thickness of a wheel's rim - the load-bearing band of steel below the tread that carries the wheel's contact with the rail. As a wheel is used and periodically re-machined (trued) over its life, the rim grows thinner. Gauging the rim confirms that enough sound metal remains for the wheel to stay in service safely.

Why It Matters

The rim must retain adequate thickness to carry car loads and to absorb the braking heat and mechanical stress of normal operation. A rim worn or machined below the allowable limit is the condemnable condition known as a **thin rim**. A thin rim has reduced strength and a higher risk of cracking or a rim or tread failure under load, which is why interchange rules set a firm minimum.

Procedure

The inspector applies a rim-thickness gauge to the wheel and reads the remaining thickness against the gauge's pass and condemn marks. A wheel with sufficient rim passes; a wheel measured as thin rim is condemned and the wheelset is removed for wheel replacement. The exact minimum rim thickness is specified in the AAR interchange rules and field manual and varies with wheel design, so the gauge itself - not a remembered number - is the authority in the field.