49 CFR § 229.75 - Wheels and tire defects.
Wheels and tires may not have any of the following conditions:
(a) A single flat spot that is 2 1/2 inches or more in length, or two adjoining spots that are each two or more inches in length.
(b) A gouge or chip in the flange that is more than 1 1/2 inches in length and 1/2 inch in width.
(c) A broken rim, if the tread, measured from the flange at a point five-eighths inch above the tread, is less than 3 3/4 inches in width.
(d) A shelled-out spot 2 1/2 inches or more in length, or two adjoining spots that are each two or more inches in length.
(e) A seam running lengthwise that is within 3 3/4 inches of the flange.
(f) A flange worn to a 7/8 inch thickness or less, gauged at a point 3/8 inch above the tread.
(h) A flange height of 1 1/2 inches or more measured from tread to the top of the flange.
(i) Tires less than 1 1/2 inches thick.
(l) A loose wheel or tire.
(m) Fusion welding may not be used on tires or steel wheels of locomotives, except for the repair of flat spots and worn flanges on locomotives used exclusively in yard service. A wheel that has been welded is a welded wheel for the life of the wheel.