49 CFR § 569.9 - Labeling of regroovable tires.
(a) Regroovable tires. After August 30, 1969, each tire designed and constructed for regrooving shall be labeled on both sidewalls with the word “Regroovable” molded on or into the tire in raised or recessed letters 0.025 to 0.040 inch. The word “Regroovable” shall be in letters 0.38 to 0.50 inch in height and not less than 4 inches and not more than 6 inches in length. The lettering shall be located in the sidewall of the tire between the maximum section width and the bead in an area which will not be obstructed by the rim flange.
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