Core temperature and surface temperature are two different tyres

The infrared reading on the pit wall screen describes a fraction of a millimetre and gets treated as the whole tyre.

A tyre is not at a temperature. It is at several, and the difference between them explains most of the confusing behaviour that gets blamed on compounds, on setup, or on the driver having a bad day.

The surface responds within a corner. Slide the car and the outer layer heats almost immediately, then sheds that heat down a straight almost as quickly. The bulk of the rubber and the air inside respond over many laps and hold their state stubbornly. So you can have a tyre with a scorching surface and a cold core, which grips for a lap and then greases up, or a tyre with a hot core and a cool surface, which feels vague for a corner and then comes alive.

Everything the pit wall sees from infrared sensors is the first case. Everything that governs long-run behaviour is the second.

This distinction explains the out lap problem. A driver on new tyres is told the temperatures are fine because the surface has come up from a burnout or from weaving. The core has not. Load that tyre hard into the first fast corner and it deflects more than expected, the contact patch shape goes wrong, and the driver reports a car that will not turn. Nothing was wrong with the setup. The tyre was not the tyre yet.

It also explains why the same compound can overheat at one circuit and never switch on at another with similar ambient conditions. What matters is the pattern of energy input, not the total. Short sharp corners with long straights between them heat the surface repeatedly and let it cool, so the core never builds. A circuit of long sustained corners builds core temperature relentlessly and can leave the surface deceptively manageable right up to the moment the whole tyre gives up.

Here is where I disagree with common practice. Teams talk about a working range as if it were one window. Treating it as two windows, surface and core, with different time constants, changes what you do. A car struggling for core temperature does not need more aggressive driving, which only burns the surface. It usually needs setup that increases sustained load, or pressure changes, or simply a longer run.

Blistering and graining are the two failures, and they point in opposite directions. Confuse them and every change you make is backwards.

The screen is telling you about the paint, not the wall.