Tire pressure, temperature, and wear in setup

The number in your garage is the cold pressure. The number that matters is the hot pressure, after two laps at race pace, and it’s several psi higher. Tires are sealed air; as the rubber and the wheel rim heat up, the air inside expands and the pressure reading climbs (ideal gas law). You set the cold number low so it rises into the optimal window once the tire is working. Set it to the target and you’ll be overinflated the whole race.

What pressure to aim for

For ACC GT3, the hot target window is 26.4–27.0 psi. Older guides quote 27.5 psi; the current optimal band is lower. You don’t set 26.4 in the garage — you set cold pressures a few psi under it and let the tires rise in. Adjust cold pressure in small steps of 0.2–0.5 psi per tire and re-check the hot reading after a clean run. ACC’s dry tires work from 70–100C, with peak grip at 80–90C.

The sim decides what you’re tuning

The biggest source of confusion is that each sim models tires differently, so advice that works in one fails in another.

• ACC is pressure-driven. Hit the 26.4–27.0 psi hot window per corner and the tire is happy. Most of your setup time goes into pressures.
• LMU is temp-driven. The tire slides until it reaches roughly 50C, optimal is 70–80C, and the out-lap genuinely feels like ice. You chase temperature, not a pressure number.
• iRacing models brake heat. In iRacing’s current tire model (NTMv10, deployed to GT3 as of 2026 Season 2 and rolled out through the 2025 GT3 tire model update and the GT4 August 2025 update), heat radiates from the brakes into the rim and adds several psi of hot pressure over a stint. iRacing’s in-game GT3 pressures also run higher than a real fast lap would, because regulation minimum pressures are often above optimal and the sim holds you to the minimum — IMSA penalizes running under it, so the floor is the target.

Reading temps across the tire

iRacing’s tire display gives you three numbers per tire: inner, middle, outer. They tell you two different things.

Middle temp is pressure, inner-vs-outer is camber

The middle temperature should sit roughly at the average of the inner and outer. If the middle is colder than the edges, pressure is too low — the tire is bowing inward and only the shoulders touch. If the middle is hottest, pressure is too high — the tire crowns and rides on its center. Fix the middle with pressure.

The inner-to-outer delta is camber. Aim for the inner edge slightly hottest, with no more than about 7C of spread (some guides allow up to 10C). Too much negative camber overheats the inner edge; too little or positive camber overheats the outer edge. Even the two edges with camber, then dial the middle with pressure. Change one lever at a time or you can’t tell which one moved the temps. See camber and alignment for the geometry.

Getting heat into cold tires

Short races and temp-sensitive models punish you on the out-lap, and the Lamborghini Huracan in particular feels light at the front when cold. Levers that build heat faster:

• Run a touch more pressure. A slightly higher cold pressure heats the air faster and gets you into the window sooner.
• Lower the spring rate. A softer spring lets the tire flex and work, generating heat through the carcass.
• Drive the out-lap harder. Weave, brake firmly, and load the tires; coasting keeps them cold for laps.

In LMU especially, accept that the first lap is on ice and don’t fight a setup problem that’s actually a cold tire.

Setup choices that extend tire life

Heat is also what kills tires. Once a tire goes red — past its window — grip drops and wear accelerates. For long stints and high-deg races (running 3x wear, endurance pacing):

• Smoother inputs. Trail off the brake, unwind the wheel progressively, feed the throttle. Sharp inputs spike tire temp and scrub rubber.
• Less camber. Aggressive negative camber that’s fast over one lap overheats the inner edge over a stint.
• Lower pressures within the window. A tire at the bottom of its pressure band puts more contact patch down and runs cooler.
• Manage temps, not just pace. Keep the tires in the window rather than above it; an overheating tire is slower and shorter-lived. This is as much a driving job as a setup one — see tire management while driving.

A workflow that works

1. Run three hard laps to get representative hot data.
2. Read the temps. Get the inner/outer edges even with camber first.
3. Then bring the middle in line with pressure.
4. Change one variable, run three more laps, re-read.

Repeat until all three numbers sit close together and the hot pressure lands in the sim’s window. That loop is the whole job.