A pyrometer is the tool you use to read race tire temperatures. A probe (needle) pyrometer pushes a tip into the rubber to read internal temp; an infrared gun reads only the cooler surface.
For setup work, use the probe. Longacre reports infrared readings run “10-40 degrees cooler than temps taken with a probe type pyrometer” and get polluted by engine and brake heat, while the probe “gets down to the cord,” where the heat isn’t skewed by outside factors. Take three readings across each tread — one about 1.5 inches from the outside edge, one in the middle, one about 1.5 inches from the inside — and get to the car fast, because the track pulls heat out quickly. Same tire order, same probe depth every time, and pre-heat the probe with a few pokes first. Inside-to-outside spread talks about camber; middle versus edges talks about air pressure.
Tire temps are the most direct read on whether your setup is working the tire, and the wrong tool gives you numbers that feel real and aren't.