Tyre pressures
and temperatures

The working window

A racing tyre is designed to work inside a narrow band of temperature and pressure. Inside that window it gives maximum grip; outside it, above or below, it grips noticeably less.

Which means there is no such thing as a good pressure in the abstract: there is the starting pressure that puts the tyre inside the window while it's working.

The two extremes:

• Below the window — cold or under-inflated. The car slides, responds slowly and the tyre deforms too much, which in turn heats it unevenly.
• Above it — over-inflated or overheated. The contact patch shrinks, grip falls, the car turns nervous and degradation takes off.

Pressure and temperature go together

The air inside the tyre heats up as you drive, and as it heats it expands: pressure rises on its own during a stint. That's the central fact to internalise.

Practical consequences:

• The pressure you set in the garage is cold. What matters is what it reads after three or four laps.
• If you start at the target pressure cold, you'll finish well above it once the tyre gets heat into it.
• The hotter the day and the more demanding the track, the more it will climb, so you must start lower.

There's also a loop: high pressure → smaller contact patch → more sliding → more heat → more pressure. That's why an over-inflated tyre degrades so fast: it feeds itself.

Reading the three zones

Most sims show tyre temperature split into inner, middle and outer. That reading is worth gold, and it's read like this:

Careful not to confuse the diagnosis: the middle-versus-shoulders split tells you about pressure; the inner-versus-outer split tells you about camber. They're different adjustments, and changing the wrong one makes both worse.

How to set them, step by step

1. Go out on the car's baseline setup and do four laps at pace. Fewer won't do: the tyre hasn't stabilised.
2. Read the hot pressures on all four corners when you come in.
3. Correct cold by the difference: if you finish half a point above target, start half a point lower.
4. Repeat until all four sit in the window. It usually takes two or three goes.
5. Adjust side to side. On a track with corners mostly in one direction, one side works harder and starts lower.
6. Check at race fuel load. With a full tank everything climbs more.

An important warning: do this before touching springs, bars or the differential. With pressures outside the window, any other change you test will give you a false conclusion.

Diagnosis by symptom

• The car slides everywhere but improves after five laps. Starting pressure too low: the tyre takes too long to come in.
• Good for three laps, then it degrades. Pressure too high: it goes past the window.
• Nervous rear as soon as you touch the throttle. Rears over-inflated, or cold.
• Won't turn in and the nose squeals. Fronts above the window, or overheated from scrubbing.
• Bounces off the kerbs. High pressure: the tyre isn't absorbing.
• Feels doughy and slow to react. Low pressure: too much deformation.

What changes during a race

Pressures aren't a set-and-forget adjustment:

• Full tank. More weight, more heat, more pressure. The opening laps are the critical ones.
• Track warming or cooling. An evening race can start at one track temperature and finish ten degrees below. You start above the window and end below it.
• Traffic. Running close behind another car adds heat, especially at the front axle.
• Safety car. Everything cools. Two very careful laps at the restart.

What you can do without pitting: manage it with your feet. If the tyre feels gone, two gentler laps bring it back; if it feels cold, move the car about on the straights and brake a little harder than usual to put heat in.

Once pressures are sorted, the next adjustment with the most impact is brake bias, and the technique that depends on it is trail braking.

Frequently asked