or more and flat spots 1 inch or longer condemn the wheel. Figure 2.8 illustrates the combination tread defects
and the proper measurements.
h. Tread-worn-hollow (Rule 76--AAR symbol
76). The tread-worn-hollow gage shown in figure
2.3 is used to measure the extent of hollow wear.
The figure also shows the proper application of the
gage to the wheel. If the nipple at the bottom center
of the gage does not touch the tread when the front
and rear bottoms are touching the top of the flange
and the top outside of the rim respectively, the
wheel is worn beyond the condemning limits.
on the nipple when it is applied, the wheel is still
safe for service. Many inspectors remove tread-
worn wheels before they reach the condemning
limits because they feel that they are dangerous and
hard on the track; however, condemning wheels
before they reach the gaged wear limits is wasteful.
It is important to note that very often when one
wheel is tread-worn, the mating wheel on the other
end of the axle has a worn flange. This develops
because the hollow tread on one wheel forms a false
Figure 2.9. Tread-Worn-Hollow Defect.
flange and tends to hold the flange of the opposite
wheel against the rail constantly.
i. Burst hub (Rule 77--AAR symbol 77). A burst hub is a radial crack in the hub. The burst or cracked
hub usually occurs when the wheel is pressed upon the axle. Three causes of the burst-hub defect are excessive
pressure, improper wheel-mounting methods, and improper taper in the wheel bore or of the axle seat. Any
wheel with a radial crack in the hub is condemnable.