Tyre Pressure

Tyre inflation pressure is the single most important routine maintenance item for tyres — affecting safety, fuel economy, tyre lifespan, and vehicle handling simultaneously. Passenger car tyres are inflated to 2.0–2.8 bar (29–40 psi) cold, with the exact specification printed on the vehicle's tyre placard (inside the driver's door sill or fuel filler flap) — not the maximum pressure moulded into the tyre sidewall, which is a structural limit, not an operating target. Tyres naturally lose approximately 0.07–0.14 bar per month through normal permeation through the rubber and bead area — meaning a tyre that was correctly inflated six months ago may be 0.4–0.8 bar low without any puncture. Pressure drops by approximately 0.07 bar for every 8°C drop in ambient temperature — seasonal temperature changes produce significant natural pressure variations that require correction. All pressure measurements must be taken cold — a tyre that has been driven more than 3 km will show 0.2–0.4 bar higher than its actual cold pressure, making hot measurements unreliable for setting correct inflation.

Correct inflation pressure maintains the tyre's designed contact patch shape and load-carrying capacity. Under-inflation allows the tyre sidewall to flex excessively on each revolution — generating heat, accelerating tread wear at both shoulder edges, and reducing fuel efficiency from increased rolling resistance. Severe under-inflation (below 1.4 bar / 20 psi) can cause the tyre to fold internally during cornering, causing a sudden blowout. Over-inflation raises the centre of the contact patch, concentrating wear on the central tread rib, hardening the ride quality, and reducing the contact patch area, which decreases grip. Correct pressure extends tyre life by 15–25%, improves fuel economy by 0.5–1.5% per 0.1 bar under-inflation corrected, and maintains the predictable handling characteristics the vehicle's suspension was calibrated for. Different pressures are specified for front and rear axles, and for different load conditions — the tyre placard always shows the correct combination for the vehicle.

Gradual pressure loss without visible puncture: Normal permeation through the tyre rubber and around the bead-to-rim seal — all tyres lose pressure slowly over time. If loss exceeds 0.14 bar per month, check the valve core for leakage (apply soapy water to the valve stem — bubbles confirm a leaking core that requires replacement) and inspect the bead area for damage.

TPMS warning light illuminated: Tyre Pressure Monitoring System has detected a tyre at 0.2 bar or more below the placard specification. Check all four tyres immediately — the TPMS warning does not identify which tyre is low on most designs, requiring measurement of all four. Do not ignore a TPMS warning and continue driving — a tyre 0.5 bar low is in the early stages of sidewall overheating.

Tyre losing pressure suddenly during driving: Puncture from a nail, screw, or road debris, or a rim impact causing bead separation. If pressure drops rapidly, steer smoothly to a safe position — do not brake hard or make sudden steering inputs with a deflating tyre.

Level 1 — Owner check: Check all four tyre pressures monthly and before every journey over 200 km. Use a calibrated gauge — stick or digital gauges are more accurate than built-in gauge/inflator combinations at petrol stations. Always measure when the tyres are cold (vehicle unused for at least 3 hours). Note the front and rear pressures from the door sill placard — they are frequently different. Add the spare tyre to the monthly check.

Level 2 — Detection: If one tyre requires repeated top-ups above the normal monthly permeation rate, check the valve core with soapy water and inspect the tread area carefully for embedded objects. A nail or screw in the tread often does not cause immediate rapid deflation — the object seals its own penetration until removed. Do not remove an embedded object until a repair can be performed immediately.

Level 3 — Professional service: Tyre repair (plug-and-patch from inside) is appropriate for penetrations in the central three-quarters of the tread area less than 6mm in diameter. Sidewall and shoulder penetrations cannot be permanently repaired — replacement is required. A tyre that has been run flat (below 0.8 bar while driving at speed) requires inspection of the internal carcass for heat damage before being returned to service — the external appearance may be normal while the carcass has been structurally damaged.