Tyre Pressures – How to check, Recommended Pressures, Everything you need to know!

Your car’s tyre pressures are incredibly important to get right since they set how much grip you have to the road. Think about it, your tyres are the only points of contact you have between you flying at 80MPH down the motorway and the ground, and having one or all of those tyres being too low or too high can mean a whole lot of danger and trouble. On top of that, having the right pressure can also save you money on fuel as your engine has to work less hard to achieve the same speeds. So, I hope it’s obvious that you should check your pressures, but how do you do that? When should you? How do you find what pressures they should be at? And how can you feel a low pressure tyre while you are driving? Well, let’s answer all those questions now starting with how to check.

The first and possibly most obvious check is the visual one. It’s really easy to take a quick look at your tyres as you get in the car, but the nuance comes from knowing what a flat tyre looks like. Is this flat? What about this? And this? Only one of those was actually low pressure and it was the last one. The first one is actually fine, but the surface is uneven and it’s a front engined vehicle so there is more weight on the front wheels making it more compressed than the rear tyre.

So, what should you be looking for? Well, on a flat, level surface, it’s normal for your front tyres to look a little more squashed if the engine is in the front of your car. A properly inflated tyre will of course not be perfectly round, but it should maintain a decently round shape without too much of a flat spot where it meets the ground. The side wall may be a little compressed and even pushing outwards slightly. A low pressure tyre will be lower to the ground and have a more obvious flat patch on the ground. The side wall might be bulging out significantly, or it could have tucked itself fully away. That’s more common on lower profile tyres.

If you suspect you might have a low pressure tyre, it’s worth checking the actual pressure. You can do that in a few different ways, my favourite is with a tiny little pressure gauge pen I keep in the pen holder in my glovebox. I like this as it’s an analogue gauge, so no batteries to run out or plastic to break, but you can buy insanely cheap digital gauges to keep with you too. I’ll leave a link to both an analogue and a digital gauge in the description if you want to pick one up yourself, they aren’t expensive and are perfect to keep in your car.

To use this, you unscrew the dust cap – keeping it safe to reinstall later – and press it down onto the stem making a good seal between the tool and the stem. The bar will rise out the back, and wherever the markings meet the body is your pressure. The same applies to digital and dial gauges, just press them on and look at the reading.

You could also use a bike pump as long as it has a gauge attached, I have a track pump which has one, the obvious benefit of this is you can immediately pump it up if it’s low. You can also use electric pumps, I have this battery powered Ryobi one and again it’ll both read the pressure, and you can have it pump the tyre back up for you if it’s low. Finally you can stop off at your local petrol station and use their pump, it does cost a little change to use but it’s there if you don’t have anything else available.

It’s important to note that if you are checking the pressure right after you’ve been driving, especially if it was a long motorway journey, your tyres are going to be warm meaning the air inside them will be too. Warm air has a higher pressure than cold air, so the pressure you read is going to be higher than if you check when they’re cold. It’s best to let them cool down first.

So that’s how to check, but how do you know what number to look for? That’s where the recommended values come in. You can find your recommended pressures on a sticker on your vehicle. It’s often in the driver or passenger side door jam, open the door and look at the edge that’s painted body-colour, outside the door seal. Occasionally it can be on the door instead again on the side edge, or in the rear door jams, on the back of the fuel filler cap or very rarely in the boot or under the bonnet. If you still can’t find it, if you have your owners manual it should be listed in there, or failing all of that you can search it online. I found Kwik Fit has a tool on their site where you put in your reg and it’ll tell you the options for your car.

When picking what pressure to use, you will want to factor in a couple of things. First is weight, the more people and luggage you are carrying, the higher the pressure you’ll need to counteract that weight. That’s normally listed on the sticker, you can see for mine it says if you only have two people and a little luggage you can run a lower pressure, but if you have a full car and boot you should inflate higher.

Another factor is speed, again something that’s often covered on the sticker, like on my old Volvo S40 it said if you only drive up to 160kph ( 99mph ) you can use a lower pressure, but if you go over 160kph you should inflate them higher.

Lastly, something that isn’t normally covered is the weather and your type of tyre. If it’s cold and wet and you have summer sports tyres like me, it can be a good idea to pick a slightly lower pressure so you have a bigger contact patch and therefore more grip even if the rubber isn’t sticking as well as it would in the dry. Lower pressures can also help reduce hydroplaning where when you drive over a puddle instead of cutting through it and staying in contact with the ground, the tyre stays on top of the water, meaning you have no contact with the ground and therefore no grip to steer or stop.

To give you a rough idea, my Audi S4 recommends between 36 and 44PSI for my tyres, but that’s on the higher end. Most vehicles I’ve worked on generally sit around 33-36 PSI, and when I say you should increase or decrease your pressures I’m talking about 3-5 PSI over or under. Any pressure that reads in the low twenties is what I’d consider ‘low’, unless your specific tyre configuration recommends that range. Anything in the tens or lower is what I’d consider dangerously low.

This is all great, but when should you be checking this? Well, a quick glance at all your tyres every time you get in the car is a good idea. You’ll notice any serious problems like a punctured tyre and save yourself getting into an accident. As for checking the actual pressures themselves, some would recommend regularly on a schedule like every couple of weeks, and that’s not a bad idea but I would throw in a few caveats. If you are just about to go on a long journey, haul something heavy, go on a track day or off roading, or the weather changes drastically like heavy rain, snow, ice or a massive heatwave it’s worth checking and adjusting as necessary.

Lastly, if you are driving, what are the signs to look for to know a tyre is low? Well, if it’s only one tyre the car will want to drift to the side that has the low pressure tyre. That’s because when the pressure drops the contact patch flattens creating more drag, meaning that side of the car will be resisting going forward more than the other. This effect can also be caused by badly aligned suspension, so it’s not a sure-fire way to know, but if you can’t drive in a straight line without steering left or right to counteract that pulling then either way you should make your way to a garage to get it fixed ASAP.

Depending on the how low the pressure is, bumps in the road may feel a little smoother than usual as the lower pressure resists the change less acting like more of a cushion, but if it’s really low you’ll basically be running on your wheel rim so the ride will get much, much harsher. If you are running on the rim you should really stop driving immediately as that’s really, really dangerous as you have next to no grip and the tyre can come unseated from the rim and rip itself to shreds or come off completely.