Correct tyre pressure should always be checked when tyres are cold — meaning the car hasn’t been driven for at least a few hours, or only a very short distance (under a mile) at low speed — since driving heats the air inside the tyre and raises pressure temporarily, producing a reading that looks fine even when the tyre is actually underinflated. This single timing detail is the most commonly overlooked part of an otherwise simple maintenance task.
Why Cold Pressure Is the Only Accurate Reading
Air expands as it heats up, and the friction and flexing a tyre experiences while driving warms the air inside it measurably within just a few minutes — enough to raise the pressure reading by several PSI compared with how the tyre sat before you started driving. Checking pressure right after a drive can mask a genuinely underinflated tyre, since the heated reading looks closer to correct than the tyre’s true resting state.
Step-by-Step
- Find your vehicle’s recommended pressure — usually printed on a sticker inside the driver’s door jamb, not the number printed on the tyre’s sidewall itself, which is the tyre’s maximum rated pressure rather than the manufacturer’s recommendation for your specific vehicle.
- Check first thing in the morning or after the car has sat for several hours, before any real driving.
- Remove the valve cap and press the gauge firmly onto the valve stem until the hissing stops and you get a steady reading.
- Compare against the door jamb sticker’s number, adding air if low or releasing a small amount if over — most gas station air pumps and dedicated tyre gauges make small adjustments easy.
- Check all four tyres, plus the spare if accessible, since pressure can vary between tyres even without an obvious symptom.
Never work under a vehicle supported only by a jack. Use axle stands on firm, level ground, chock the wheels that stay down, and leave the car in gear or Park with the handbrake on. A jack lifts; stands hold.
Why the Door Jamb Number, Not the Tyre Sidewall Number
The number molded into a tyre’s sidewall is the maximum pressure that specific tyre model is rated to hold safely — not the pressure your vehicle’s suspension and handling were actually tuned around. Manufacturers calculate their own recommended pressure specifically for how that vehicle rides, handles, and wears tyres, which is usually lower than the tyre’s maximum rating and is the number that actually matters for your car.
How Often to Check
- At least once a month, since tyres naturally lose a small amount of pressure over time even with no puncture.
- Before any long trip.
- With any significant temperature change — pressure drops roughly 1 PSI for every 10°F drop in outside temperature, which is why tyres commonly read low on the first cold morning of the season even with no actual leak.
- Alongside routine service like an oil change or tyre rotation, a natural moment to check while the car is already up.
What Happens If You Get It Wrong
Underinflated tyres wear unevenly on the outer edges, generate more heat, and slightly increase fuel consumption, while overinflated tyres wear the center of the tread faster and reduce grip and comfort — see our reading uneven tyre wear patterns guide for what these specific wear patterns look like once they’ve developed. Persistently low pressure can also eventually trigger the TPMS warning light.
When to See a Mechanic
Not needed for routine pressure checks — this is a genuinely simple DIY task. Worth a visit if one tyre consistently reads low compared with the others, which can indicate a slow leak worth investigating. More in our maintenance section.
Frequently Asked Questions
When should I check my tyre pressure?
When tyres are cold — first thing in the morning or after the car has sat for several hours, before any real driving, since driving heats the air inside and temporarily raises the reading.
Should I use the pressure printed on the tyre or the door sticker?
The door jamb sticker — that’s the manufacturer’s recommendation tuned for your specific vehicle. The tyre sidewall number is just that tyre’s maximum rated pressure, not a recommendation.
How often should I check tyre pressure?
At least once a month, before long trips, and with any significant temperature change, since pressure drops roughly 1 PSI for every 10°F drop in outside temperature.
Why does my tyre pressure warning light come on in cold weather?
Cold air contracts, lowering pressure enough to trigger the TPMS light even without an actual leak — this is normal and simply means the tyres need a top-up for the colder temperature.
What happens if my tyre pressure is wrong?
Underinflated tyres wear the outer edges faster and reduce fuel economy; overinflated tyres wear the center faster and reduce grip and comfort.
