Tire truing is machining an RC tire on a lathe so it runs perfectly round, to a chosen diameter and profile. ROAR's on-road rules allow truing but ban the scaly texture a lathe can leave on the contact patch.
ROAR’s GT12 rule (§1.8.1) draws the line cleanly: “The contact-patch surface of all rubber tires must be uniformly smooth and show no sign of artificial texturing (i.e., resembling fish scales, snake skin, or alligator hide).” The Formula One section (§1.11.4) repeats it almost verbatim for “rubber tire slicks.” Notice what’s regulated — the surface you hand to tech, not the machine. ROAR says those textures “frequently occur when using a mechanical tire truing machine to skim or resurface the contact patch” and “must be completely removed” before inspection, so true the tire, then take a light finishing pass. Truing also shrinks diameter, which moves rollout, so recheck gearing afterward. Whether truing is normal at all varies by class and surface; read your own class section.
Truing buys you a round tire and a repeatable rollout, but leaving the lathe's texture on the contact patch hands tech an easy reason to fail you.