Optimal tyre pressures

Cold pressure vs hot pressure — mind the gap

There are two pressures, and confusing them is the most common tyre mistake there is. Cold pressure is the number you dial into the garage before you run — the "set" pressure. Hot pressure is what the tyre actually reaches once it has heated up on track: as the tyre flexes and the carcass warms, the air inside expands and the pressure climbs several units above the cold value.

The gap matters because grip lives at the hot pressure, not the cold one. The tyre only performs once it is up to temperature, so the cold number is just a means to an end — you set it on purpose so that the tyre lands inside its hot window when warm. Set the cold pressure by feel and you are aiming at the wrong target.

The hot pressure window — where grip peaks

Every compound, on every car, has a narrow band of hot running pressure where the tyre reaches its grip peak. That band is the hot pressure window, and the whole game is landing inside it. Sit above it or below it and you leave grip on the table — and you usually overheat part of the tread while you're at it.

• Too low — the tyre rolls over onto its shoulders, the carcass flexes too much, the car feels sluggish and vague, and the edges of the tread overheat from doing all the work.
• Too high — the contact patch crowns up onto its middle, the car goes skittish and nervous, you lose mechanical grip, and the centre of the tread overheats while the shoulders stay cool.
• In the window — the load spreads evenly, the tread sits flat, temperatures are even across the face, and the tyre gives everything it has — and holds it for the stint.

Pressure shapes the contact patch — read it with camber

Pressure decides how the tyre's footprint — the contact patch — sits on the road, and that footprint is where every bit of grip comes from. Under-inflated, the patch bulges at the shoulders and goes light in the middle, so the edges do too much work and run hot. Over-inflated, the patch crowns up so the middle carries the load and the shoulders go light, so the centre runs hot. Right in the window, the load is spread evenly and the whole tread works at the same temperature.

This is why pressure is never read alone. Pressure and camber together shape the inner / middle / outer temperature spread across the tread. Camber tilts the tyre so it sits flat under cornering load; pressure sets how the patch bulges or crowns. Read the three-zone temperature spread and you can tell which of the two is off — and the engineers always read them as a pair, never one in isolation.

Pressure as a balance lever — front/rear and left/right

Once both axles are roughly in their window, the front-versus-rear pressure split becomes a fine balance lever. Push one axle out of its window and it loses grip relative to the other — too much front pressure can add understeer, too much rear can free the rear and add oversteer. Inside the window the effect is subtle; the moment you stray outside it, the effect is large and the tyre starts to overheat, so this lever lives at the edges of the window, not deep inside it.

There is a second axis on certain tracks. On ovals and circuits with long, single-direction corners, one side of the car works far harder than the other and heats its tyres more. That is where a left-versus-right pressure split earns its keep — you can bleed pressure off the side that is building heat and pressure fastest so both sides land in the window together. On a normal road course with corners both ways, you keep left and right symmetric.

Start cold, build into the window — over a stint

Because pressure climbs as the tyre heats, you don't set the pressure you want — you set a cold pressure that grows into the one you want. The tyre builds pressure over the first few laps, then settles once it reaches a steady running temperature. The target is to have it land in the window when hot and stay there for the bulk of the stint, not just for one flying lap.

What the engineers read — then prescribe

Pressure is only the right answer once you know where the tyre sits on its window and how its tread is heating. SimRace.app pulls your full setup and a stand of specialist race engineers log the telemetry — they read your hot pressures against the target window and the cross-tread temperatures (inner / middle / outer) for each corner, so they can see whether you are low, high or in the window, and whether the tyre is rolling over or crowning.

From that they prescribe the move: the cold change that lands the hot pressure in the window, and whether a tread that is hot on one zone is a pressure problem or a camber one. They watch it over a stint too — a tyre that starts in the window and climbs out of it is a different fix from one that never gets there. And because pressure couples to heat, they read it alongside how hard you are working the tyres in braking, which ties into the brake thermal window as well.

FAQ

The setup glossary

Tyre pressure is one lever among several that shape the contact patch and the tyre's temperature. Read the rest, one page at a time:

• Camber
• Toe in & toe out
• Brake thermal window
• Mechanical balance
• The full setup guide →