· 3 min read
Track tyre pressures: the target is hot, not cold
Setting cold pressures is setting blind. How to aim at a hot target, and why it has to be recorded circuit by circuit.
You spend the day dropping 3 psi, then adding 1 back. By late afternoon the car finally works. The following year, at the same circuit, you start from scratch.
The problem isn't the adjustment. It's that you're setting the wrong quantity, and not recording the right one.
The pressure that matters is the hot one
A track tyre works at its operating temperature. Pressure rises 6 to 12 psi from cold, depending on the tyre, the circuit and the pace.
Cold pressure is therefore not a setting: it's a starting point chosen to reach a hot target. Two days at the same cold pressure — one at 45 °F in November, one at 90 °F in July — will produce very different cars.
Rough figures, to be adjusted per tyre:
- sporting road tyre: 35–38 psi hot;
- semi-slick such as AR‑1, R888R, Cup 2: 29–33 psi hot;
- slick: 23–28 psi hot, with precise manufacturer recommendations — follow them, they're reliable.
To get there you generally start 6 to 9 psi lower cold, then correct session by session.
Reading the tyre rather than the gauge
The gauge tells you the pressure. The tyre tells you whether it's working.
Over-inflated: wear concentrates in the centre of the tread, grip feels vague, the car slides at all four corners. The tyre runs cool because it flexes little.
Under-inflated: wear rolls over onto the outer shoulder, steering goes soft, and temperature climbs excessively — under-inflation destroys a semi-slick far faster than over-inflation does.
The most useful marker: the wear indicators on the shoulder. If the tyre is running past them, it's short of pressure or of camber.
A needle pyrometer changes everything: three readings per tyre — outer, centre, inner — straight after the session. A centre more than 18 °F hotter than the shoulders means over-inflation; the reverse means the opposite.
What moves the target
Ambient and track temperature. The dominant factor. The same setting behaves differently at 60 °F and 95 °F.
Rain. Raise pressure to sharpen the contact patch and cut through standing water — typically 3 to 4 psi more.
The layout. A circuit with long right-hand loads overworks the front-left, which will climb higher than the rest. Adjust corner by corner, not axle by axle.
The pace. Three sighting laps don't heat a tyre the way twenty minutes of attack does. A pressure taken after a gentle session will mislead you.
The habit that saves next year
Record, every session: cold starting pressures, hot pressures on coming in, ambient temperature, track condition, and one sentence on how the car felt.
Three numbers, one minute. That's what makes the next visit to the same circuit start from a setting that already worked instead of rebuilding the whole day.
Nobody does it, because the notebook stays in the car while the phone is in the driver's pocket — and because a note lost in a notes app is never found again.
StemmaPass keeps these settings per circuit. The setup log records pressures, camber and suspension settings alongside the session they belong to — and offers you the last setup used at that circuit when you go back. It's the most ordinary feature in the product and the one users most often say they'd been missing.