How to Check Your Tire Pressure Properly (and Why It Matters)

A friend of mine works at a tyre fitter just outside Sheffield. Every time I see him he tells me the same thing. The single most common cause of premature tyre wear that he sees is not bad roads, not aggressive driving, not cheap tyres. It is owners who never check their pressures. He says he can tell, within thirty seconds of looking at a tyre, whether the owner has touched a pressure gauge in the last six months. The shape gives it away.

It is one of those small jobs that has a wildly disproportionate effect on the car. Correct pressure improves fuel economy, extends tyre life by years rather than months, shortens braking distance, and reduces the risk of a blowout on a hot day. Getting it wrong is what makes a set of tyres last twenty thousand miles instead of forty.

Why pressure changes when you are not looking

Tyres lose pressure all on their own. Even a perfectly sealed tyre loses around 1 to 2 PSI per month through the rubber itself, a process called permeation. Add a small slow leak from a tiny piece of grit in the tread, the natural expansion and contraction of air as the seasons change (a tyre loses roughly 1 PSI for every 10 degrees the temperature drops), and the gentle stretching of the rubber over time, and you have a recipe for a tyre that started the year at the correct pressure and ends the year noticeably soft.

This is why an annual MOT check is not enough. Pressures need attention monthly. It is also why the tyre that looked fine when you parked the car last summer may be visibly low when you walk out to it on a frosty November morning.

Find your correct pressure (not the one on the tyre)

There is a number written on the sidewall of every tyre, usually in the form of “MAX PRESSURE 51 PSI” or similar. This is not your tyre pressure. It is the maximum the tyre can safely hold. Using this number is one of the most common mistakes drivers make, and it will give you an over-inflated tyre that wears in the centre and rides like a brick.

The correct pressure for your car is set by the manufacturer of the vehicle, not the tyre. You will find it in one of three places: a sticker inside the driver’s door jamb, a sticker inside the fuel filler flap, or in the handbook. The figure will usually be different for front and rear tyres, and there is often a higher number for “fully loaded” use, meaning four passengers plus luggage. Use the standard figure for everyday driving and the loaded figure when you actually have a full car.

The four-minute check

You need a gauge. Petrol station gauges are free and roughly accurate. A small handheld digital gauge from a car parts shop costs under a tenner and is more reliable. If you can afford it, the handheld one is a much better long-term investment.

Check pressures when the tyres are cold, ideally first thing in the morning before you have driven anywhere. Driving warms the tyres, which raises the pressure by 4 to 6 PSI and gives you a misleading reading. If you have to drive to a petrol station to use the air, do it on a short trip and accept that your reading will be slightly high.
Unscrew the dust cap from one valve. Keep it somewhere you will not lose it, because the dust cap is what stops grit working its way into the valve and causing a slow leak.
Press the gauge firmly onto the valve. There will be a brief hiss as it seats; this is normal. Hold it for two seconds, then read the figure. If it is low, attach the air pump and add air in short bursts, rechecking after each one. If it is high, press the small pin in the centre of the valve gently to release a little air, then recheck.
Repeat for all four tyres. Do not forget the spare, if you have one. A spare that is flat when you need it is the cruellest joke a car can play on you.
Screw the dust caps back on.

The signs of a tyre that has been wrong for a long time

You can read a tyre’s history from its tread wear. Spend two minutes looking at the wear pattern on each of your tyres and you will know more about how it has been treated than the previous owner ever told you.

Worn in the centre, fresh at the edges: chronic over-inflation. The tyre is rounded, only the middle is touching the road.
Worn at both edges, fresh in the centre: chronic under-inflation. The tyre is squashed flat, the centre lifts away from the road.
Worn on one edge only: the wheel alignment is off. The tyre is being dragged sideways slightly with every revolution. This needs a tracking adjustment, which is cheap and quick at a tyre fitter.
Cupped or scalloped wear (small dips around the tyre): worn suspension or unbalanced wheels. A tyre fitter can tell you which.

The nitrogen question

Some tyre fitters offer to fill your tyres with nitrogen instead of air, usually for a few pounds extra. Nitrogen molecules are very slightly larger than oxygen molecules, so they leak out of the tyre wall a bit more slowly. In a Formula 1 car or on a long-haul aircraft, where pressure stability matters intensely, this is meaningful. On a Vauxhall Astra in Surrey, it is largely marketing. Normal compressed air is already 78 percent nitrogen. Save your money. Check your pressures monthly with normal air and you will get the same result for free.

Why this matters for fuel and money

Under-inflated tyres increase rolling resistance. A tyre that is 8 PSI low, which is a very common state of affairs for cars that are never checked, can reduce fuel economy by 3 to 4 percent. Over a year of average driving, that is enough to buy a decent meal out. Over the life of the tyres, you are also losing roughly a quarter of the tread life, which means replacing a set of four tyres a year earlier than you needed to. The total cost of never checking your pressures, across the life of one car, comfortably runs into four figures.

For a similar low-effort habit that pays back over years, our piece on the right way to care for a laptop battery follows much the same logic applied to a different object. The principle, small monthly attention prevents large eventual cost, is the same one.

What to do when a tyre keeps going soft

If you check a tyre, inflate it correctly, and find it visibly low again within a week or two, you have a slow leak. The three usual causes are a slow puncture (often a small nail or piece of glass that has worked its way in), a corroded valve, or a slow leak between the tyre bead and the wheel rim. None of these are dangerous in the short term if you keep an eye on pressure, but all of them need a tyre fitter. A slow puncture caught early can usually be plugged or patched for under twenty pounds. Left for months, it eventually fails, either as a sudden flat in an inconvenient place or as a damaged sidewall that means a whole new tyre.

Tyre pressure is one of those small, dull, repeating jobs that almost nobody enjoys, and yet it pays back more than almost any other car-care habit. Four minutes a month, eight tyres a year if you count the spare, and you will get years of extra life out of every set of tyres you ever fit.

For a related angle, our piece on How to Prepare Your Car for Winter (Without Spending a Fortune) covers a closely connected problem.

Frequently Asked Questions

My car has a tyre pressure monitoring system. Do I still need to check manually?

Yes. TPMS systems vary in quality, but most only warn you when a tyre is significantly under-pressure, often 20 to 25 percent below the recommended figure. By that point the tyre has already been wearing badly for weeks. The light is a last-resort warning, not a maintenance tool. A monthly manual check catches small drops before they become big ones. Treat the TPMS light as the equivalent of a smoke alarm: useful in an emergency, but no substitute for not setting fires.

How accurate are petrol station pressure gauges?

Variable. The newer digital ones at supermarket petrol stations are usually within 1 to 2 PSI of correct, which is good enough for ordinary use. The older analogue ones at small garages can drift quite badly and may read 3 to 5 PSI off. The simplest test is to check the same tyre with two different gauges and see if they agree. If you want to be sure, buy your own handheld digital gauge for under a tenner and use the petrol station compressor only to add air, checking the actual pressure with your own gauge each time.

Should I increase tyre pressure in winter or decrease it?

Pressures drop naturally as temperatures fall, roughly 1 PSI for every 10 degrees Celsius. So in winter you will need to add air to bring tyres back up to the same figure the manufacturer recommends. Use the same standard pressure year-round. Do not deliberately over-inflate in winter or under-inflate in summer. The manufacturer's recommended pressure is the correct one regardless of season. Just check more often in winter, because the changes are bigger and faster.

Is it dangerous to drive on slightly under-inflated tyres?

Slightly under, by 2 or 3 PSI, is more wasteful than dangerous in the short term. Significantly under, by 8 PSI or more, becomes genuinely risky, especially at motorway speeds. Under-inflated tyres heat up much faster, and an overheated tyre can fail catastrophically. The sidewalls also flex more, which makes the car handle vaguely and lengthens braking distance. If you suspect a tyre is significantly low, do not drive at speed until you have added air. A petrol station detour is always cheaper than a blowout.

What pressure should I use if my car has different size tyres front and back?

Some performance cars and rear-wheel-drive sports cars use different tyre sizes front and rear, and the manufacturer will specify different pressures to match. Always use the figures on the door jamb sticker or in the handbook, which will list both. Never just average them or use the higher number for both. If you have replaced the original tyres with a different size, the original pressure recommendation may no longer apply, and a tyre fitter can advise on the correct figure for your new setup.

Senior Contributor

Smit Sharma

Smit Sharma writes and edits Repair Habit. He is not a licensed technician of anything. What he knows about repair he picked up the ordinary way: watching his father fix things around the flat rather than throw them away, spending two summers as an apprentice in a small electronics shop, and, once he had his own place, running through the mistakes himself on his own washing machine, kettle, chairs, and car. He is a working parent, a slow buyer of new things, and a slightly obsessive maintainer of the ones he already owns. He does not believe repairing your dishwasher makes you a better person. He believes it is often the cheapest and quietest response to a small problem, which is roughly all the philosophy this site carries.

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