How to Check and Inflate Your Tire Pressure

Tire pressure is the most neglected thing on a car and one of the few you can fix yourself in five minutes. Underinflated tires wear out faster, use more fuel, and handle worse — particularly in an emergency stop.

Where to find your correct pressure

Here's the part most people get wrong: the number on the tire sidewall is not your target pressure. That's the tire's maximum safe pressure, not what your car is designed to run.

Your actual figure is on a placard, usually in one of these places:

  • Inside the driver's door frame
  • Inside the fuel filler flap
  • In the glovebox
  • In the owner's manual

The placard often lists two figures — normal load and full load. If you're carrying passengers and luggage, use the higher one. Front and rear can differ. Follow the placard, not the sidewall.

Check them cold

Pressure rises as tires heat up with driving. The manufacturer's figure assumes cold tires — parked for at least three hours, or driven less than a mile or two.

Check warm tires and you'll read high, let air out to "correct" it, and end up genuinely underinflated once they cool. If you can only check warm, expect the reading to be a few PSI above cold, and don't bleed it down to match the placard.

How to inflate a tire

  1. Park somewhere safe and level. Handbrake on, engine off.
  2. Unscrew the valve cap and keep it somewhere you won't lose it — pocket, not roof.
  3. Check the current pressure with a gauge or the inflator's built-in display. Press the connector on squarely; a brief hiss as you connect is normal, a continuous hiss means you're not seated properly.
  4. Set your target if the inflator has a preset, or watch the gauge if not.
  5. Inflate. Portable inflators take a few minutes per tire. Larger tires take longer.
  6. Recheck once done — disconnect and take a clean reading.
  7. Overshot? Press the small pin in the centre of the valve briefly to release air, then recheck.
  8. Replace the valve cap. It keeps dirt and moisture out of the valve.
  9. Do all four — and check the spare, if you have one. A flat spare is a nasty surprise.

How often?

Once a month is a reasonable habit, plus:

  • Before any long drive.
  • When the weather turns cold. Pressure drops roughly 1 PSI for every 10°F (about 5.5°C) fall in temperature. A cold snap can quietly put every tire below spec — which is why TPMS lights cluster on the first frosty morning.
  • When carrying a heavy load.
  • Whenever the TPMS light comes on.

About that TPMS light

The tire pressure warning light typically triggers at around 25% below the recommended figure. That's not an early warning — it's already meaningfully underinflated by the time it lights up.

A light that flashes on startup then stays solid usually indicates a system fault rather than low pressure — worth getting looked at.

Don't rely on TPMS as your only check. It catches problems late by design.

Why it's worth the five minutes

  • Tire life. Underinflation wears the shoulders and can noticeably shorten tire life.
  • Fuel economy. Soft tires have more rolling resistance, costing you a little on every trip.
  • Braking and handling. Underinflated tires flex more and respond less predictably — the difference shows up exactly when you need it most.
  • Blowout risk. Underinflation causes heat build-up, and heat is what destroys tires at speed.

When not to inflate

Air isn't always the answer. Get professional help if:

  • The tire keeps going down. A slow puncture needs repair, not repeated topping up.
  • There's visible damage — a bulge in the sidewall, a cut, or an embedded object. A sidewall bulge means structural damage; that tire needs replacing, not inflating.
  • The tire is completely flat. Driving on a flat, even briefly, can wreck it and the wheel. And a tire that's gone fully flat may have unseated from the rim — that needs a workshop.
  • You're on a motorway hard shoulder. Don't. Get behind a barrier and call for assistance.

Keeping an inflator in the car

A portable inflator turns a low tire from a problem into a five-minute stop — no hunting for a service station with a working air line, no queuing, no correct change.

Look for a built-in gauge, a preset cutoff so it stops at your target, and a light if you might use it at night.

Since low tires and flat batteries are the two most common roadside problems, a device that handles both is one thing in the boot instead of two.

See the RoadReady All-in-One Jump Starter & Tire Inflator →

Related guides

Common questions

PSI or bar?
Same thing, different units — 1 bar is about 14.5 PSI. Most inflators switch between them. Match whatever your placard uses.

Should I use nitrogen?
Nitrogen leaks marginally slower and is less affected by temperature. For everyday driving the benefit is small. Regular air, checked regularly, beats nitrogen you never check. You can top up nitrogen-filled tires with air in an emergency.

Why does one tire keep losing air?
Slow puncture, a leaking valve, or a poor seal at the rim. Get it inspected — topping it up weekly is treating the symptom.

Can I overinflate?
Yes. Overinflated tires wear in the middle, ride harshly, and reduce grip. Follow the placard.

Do I check the spare?
Yes, and almost nobody does. Spares lose pressure sitting unused. Space-saver spares often need much higher pressure than normal tires — check the sticker on the spare itself.

General guidance only — always follow your vehicle placard and owner's manual. If a tire is damaged, bulging, or repeatedly losing pressure, have it inspected by a qualified tire professional. Never attempt roadside tire work in an unsafe location.

Back to blog