The number on the tyre is a maximum. The number you need is on the car.
Two numbers get confused and only one of them is useful. The big one moulded into the sidewall — 44 PSI, 3.0 bar, whatever yours says — is the structural limit of the tyre, the pressure at which it is rated to carry its maximum load. It is not a recommendation and inflating to it is not "safe". The number that matters is on a sticker on the driver's door pillar, or inside the fuel flap: the pressure the car maker wants for that car, at that weight, cold, usually 2.1–2.5 bar for a passenger car and a bit more for something heavy or electric. Front and rear are often different, and there is usually a second row for a full load.
And "cold" is a definition, not a mood: parked at least three hours, or driven less than about two kilometres. That is the condition the car maker's number refers to, and it is the only condition in which a reading can be compared to it.
Why the reading you took was the wrong reading
Air expands when it is warm, and a tyre gets warm from being driven — 20 to 40 minutes of motorway will do it. The result is that a hot tyre reads 0.2 to 0.3 bar higher than the same tyre cold. Put those two facts together and you get the single most common mistake on this page: you come off the motorway, pull into a petrol station, check the pressure, see 2.6 against a spec of 2.4, and conclude everything is fine. It is not. Cold, that tyre is at about 2.2 — a fifth of the way to a warning light, and already costing you fuel and shoulder wear.
The same physics runs the other way with the seasons and explains the light that comes on every November. Pressure falls about 0.1 bar per 10 °C of temperature drop, so a car set correctly in a warm September is 0.3 bar down by the first cold snap — and most warning systems trigger at roughly 0.4 bar below spec, or 25 per cent. Nothing is broken. Nothing needs buying. It needs air. But note the corollary, which is where people go wrong in the other direction: never let air out of a hot tyre. If it reads high because it is hot, releasing air until it matches the spec leaves it under-inflated once it cools.
The one test that separates weather from a puncture
Count how many tyres are low. Four tyres do not all get punctured in the same week, and they do not all lose the same amount. If all four are down by a similar amount, and it correlates with a cold spell, it is temperature — inflate and move on. If one tyre is low and the others are at spec, that is a leak, and the only question is where.
Rate matters too. Slow seepage through the rubber and the valve is normal, and a tyre can lose a little over months without anything being wrong. The line worth using is about 0.3 bar in a week: faster than that, or a tyre that goes down again shortly after being topped up, is losing air somewhere it should not. To find it, mix washing-up liquid with water, brush it generously over the valve, the bead where the tyre meets the rim, and the whole tread, then watch. Bubbles are the answer, and they will find a nail the eye misses. Check the valve stem especially — a cracked or perished rubber valve is a classic slow leak that people replace tyres over.
Both directions are wrong, and over is the more popular mistake
Under-inflation flexes the sidewall far more than it was designed for, which heats the carcass, wears both shoulders, raises rolling resistance and — at motorway speed on a hot day — is the classic route to a blowout. Over-inflation shrinks the contact patch, so the centre of the tread wears while the edges do not, wet braking gets longer and the ride gets harsh, which also makes potholes more expensive. Neither is a good trade for a fraction of a mile per gallon, and the car maker already balanced fuel, comfort, wear and grip when they chose the number on the sticker.