Car Tyre Pressure Guide

Having the correct car tyre pressure can improve fuel efficiency, driving stability and improve safety. Find out why it's important to check regularly.

The Importance of Car Tyre Pressure Maintenance

One thing that is constantly forgotten when it comes to car maintenance is car tyre pressure. Most car owners nowadays are more in tune with keeping up with car maintenance checks; oil, coolant, screenwash, brake fluid etc are all big checks but people often forget the most important part of your car is the shoes it uses to slide along the harsh tarmac.

Did you know that the incorrect car tyre pressure can cause rapid wear of your tyre tread, cause flat spots to appear or cause your wheels to become misaligned due to road conditions? In this post, we here at Stable Lease will talk about the do's and don'ts when it comes to car tyre pressure.

Essential Tyre Pressure Tools

First and foremost, it's worth getting the correct tools sorted before reading further, as without the correct ones you will have trouble fixing your tyre pressures.

1. Tyre pressure gauge

You can get these from most car parts sellers. Essentially they take your cars tyre BAR or PSI reading and inform you of what it's at. These come in 2 forms, digital and analogue, digital being more expensive but generally more accurate, and analogue being cheaper but less accurate. Our personal suggestion is to go for an analogue as they're cheap and don't need batteries. You can get an analogue gauge for around £12. AutoExpress has a good list of digital and analogue gauges you can buy.

Note: BAR and PSI are 2 different types of measurements for recording car tyre pressure. For this reason, it's extremely important to know which measurement is which when reading your car's manual. For example, 33 PSI would be 2.2 BAR. You can do conversions with this PSI to BAR calculator here.

2. Car air pump

The most obvious tool you'll need is some form of air pump in order to get more air in your tyres if they're under-inflated. You can get car tyre pressure pumps from plenty of different places and prices generally range from £10 - £40, from manual pumps that involve physically pushing down on the pump to automatic ones that draw power from your V12 socket. Again, unless you prefer the ease of an automatic pump we'd go for a manual hand or foot pump as they're far cheaper and do the same job at the end of the day. 

3. Valve dust caps

Dust caps are the plastic tops that cover your car tyres important valves. It's not common to see cars just missing a dust cap and whilst the valves themselves don't leak air or let water in even without the cap off, rocks and other objects can strike the valve and damage it, which leads to leaky valves. Having spare dust caps ensures you can always replace any that end up going missing or replacing damaged caps, as they often end up become cross threaded.

4. Gloves or a towel

Anyone that has done this job before knows that any unprotected hands unscrewing a dust cap off are going to end up with black fingers. All the dirt and grime that end up on your wheels during use also stick to the valve and dust cap. From personal experience, you definitely don't want to spend 5 minutes trying to wipe the sticky muck off your hands after unscrewing a cap without gloves or a towel at hand, especially in winter! 

5. Tyre tread gauge

Do you know your cars legal tread mm limit? Not many do and you don't want to get in trouble during a routine police stop and risk a fine. 1.6mm is the legal limit for your cars tyre tread and you can check this with a tyre thread gauge. These are relatively simple products that measure your tyre's tread simply by inserting them into your tyres groves and the tool will tell you how much tread you have left by inserting them into the groves of your tyre.

6. Tyre Pressure Monitoring System (if you have one!)

If you have a modern built car you may not know that you have a built-in system that monitors your car tyre pressure. Usually found in the settings of your cars infotainment system, here you can set the default tyre pressure, meaning that if your car suddenly starts to lose air from a puncture or tyre damage, the system will bring up a warning on your screen. This is s good way to keep an eye on your car tyre pressure, but I wouldn't rely on it too much as it only shows a warning when you drop a considerable amount of pressure.

Got everything? Good. Let's move on.

Understanding Car Tyre Pressure

Each car and tyre has a specific set of conditions that are set by the manufacturer to ensure maximum preservation of tyre wear, road safety and fuel consumption. Following these will ensure that you get the most out of your tyres, especially given that many cars have expensive tyres such as performance cars (though generally, people aren't as interested as saving tyre life in performance cars!). Having the correct car tyre pressure will mean your tyres will last the full length of their life, increase your vehicle's safety when driving daily and helps save on economy when it comes to fuel consumption.

It's important to note that car tyre pressure changes based on certain circumstances. For example, did you know that when the sun is out on a hot summers day, your tyres can actually rise 10 PSI levels even when stationary? Another example is car tyre pressure should change when you know you are going to be carrying a lot of weight inside your vehicle. Carrying 7 passengers in a people carrier car? The rear tyres may need to be 42 PSI instead of the normal 36 to account for this. Be mindful of conditions like this can help prolong the life of your tyres and improve the safety of your vehicle. 

Let's have a look at types of conditions that can arise from improper tyre maintenance.

Under-inflated tyres

Under-inflated tyres are tyres that are below the recommended BAR or PSI setting. Being slightly below won't do too much harm, but having 20 PSI on your front tyres when they're meant to be 33 PSI can have some avoidable consequences. Under-inflated car tyre pressures can:

• Lead to rapid wear of your tyres on the outer edges
• Increase the likelihood of a tyre blow out
• Increase fuel consumption and decrease MPG
• Increase 0 - 60 time due to friction

Rapid wear of your tyres occurs essentially due to increased friction between the road and your car tyres. Increased wear means that you will be purchasing new tyres at a faster rate and make it possible that your increased tread wear may go unnoticed, meaning you may accidentally go below the legal limit. A good indicator that your car tyre pressure is under-inflated is when the outer edges of your tyre are wearing faster than the centre. This happens due to the edges of your tyres are more likely to be pressed against the road when under-inflated due to the nature of the tyres holding up a heavy vehicle at the wrong pressure.

Tyre blowouts occur when a car tyre pressure is under-inflated significantly. Though rare blowouts are incredibly dangerous with the potential to cause crashes, and a massive reason for you to monitor your tyre pressure. Blowouts occur due to the tyres being compressed beyond the usual limits due to under-inflation, this causes flexing within the makeup of the tyre and essentially heats the tyre up far beyond the correct amount. A buildup of heat in this way is what can cause a blowout and is more likely to happen when your under-inflated tyre is moving at a considerable speed such as 60mph (where the tyre is likely to be at maximum heat and friction.

Has your MPG (miles per gallon) suffered recently? A good indicator of under-inflated car tyre pressure is decreasing MPG and increasing fuel consumption. This happens with under-inflated tyres because as the tyre pressure gets less and less there's a greater area of tyre surface pressing against the road, thus increasing the friction between the road and tyre and making the car work harder to move. This is a recognised term called 'rolling resistance' and causes a significant rise in fuel consumption due to you car having to work harder to maintain speed. TopSpeed reports that an estimated 8.1 billion litres of fuel are wasted per year due to under-inflated tyre pressures.

If you drive a performance car and you're all about that 0 - 60 time your tyre pressure could be stopping you. Similarly to fuel consumption as mentioned above, the increased friction against the road due to rolling resistance can actually decrease your ability to speed up faster.

So in conclusion under-inflated car tyre pressure sees increased fuel consumption, the increased potential of a tyre blowout, increases 0 - 60 times and causes rapid wear of your tyres. But all in all, the place that is hit the hardest is your wallet due to having to pay for more fuel and paying out for tyres more often.

Over-inflated tyres

On the opposite end of the spectrum, we have tyres that have had too much air put in them, causing them to be over-inflated. Having over-inflated car tyre pressure can bring its own set of problems and consequences. Over-inflation means when your air pressure inside your tyres is far over the recommended setting. Having an air pressure of 40 PSI when your recommended is 33 PSI would count as over-inflated. Here's what over-inflated car tyre pressure can cause:

• Causes rapid wear on the centre of your tyres
• Wheel alignment can go out due to road hazards
• Danger of losing control at high speeds due to less tyre friction

Unlike under-inflated tyres, over-inflated actually, have less friction between the road and the tyre due to the majority of the surface pressing against the centre of the tyre. This means that away from the centre of the tyre the tread is less likely to come into contact with the road, meaning all of the wear is going to happen in the centre. This isn't a good balance as the weight of the vehicle is pressing down on a single section of your tyre, causing it to wear in the middle far faster than normal. 

When driving at speed with over-inflated tyres, they're more likely to be affected by road hazards such as potholes, large rocks and other usual road hazards. Hitting a pothole at speed with over-inflated tyres commonly causes cuts and bumps along the tyre which weaken the structural integrity and cause lead to blowouts as the tyre flexes. One important thing to keep an eye on is large 'bulges' along the tyre. These happen when you hit a pothole or other road hazard at such speed that it causes a deformity to occur within the tyre. A tyre with one of these bulges is more likely at risk to have a blowout due to weakening structural integrity.

Driving on such a small section of the tyre when over-inflated means there's less friction between the tyre and the road. This is turn means when driving at high speeds there is a higher chance of potentially losing control of the car. Driving in rainy conditions with over-inflated car tyres can also cause an increased chance of aquaplaning, which is when your tyres completely lose friction with the road and essentially slide across the surface water along the road.

In conclusion, there are some serious consequences to having your tyres over-inflated. Not only is it hitting your wallet again due to having to change your tyres more often due to wear and hazard damage, you're also increasing the likelihood of having a crash whilst travelling at higher speeds.

Car Tyre Pressure Changing Instructions

If you've read the essential tools section above, you'll be ready to tackle the next step which is checking, or changing your car type pressure. You can complete this task in around 10 - 20 minutes. First things first, you need to. know the correct settings for your car. You can get the correct car tyre pressure settings by:

• Checking your vehicle's manual within the tyre section
• Checking around the outer edges of the tyre, it usually has the recommended pressures
• Checking inside the petrol cap sometimes has a sticker with tyre pressures on
• Using Google to check your model (be careful of finding wrong information though)

As mentioned previously, the BAR os PSI is heavily dependent on your vehicle load. If you're carrying lots of people then you need to find the "fully laden" pressures rather than the standard pressures. For example, an Audi A4 coupe standard pressures are 34 PSI front and 37 PSI rear. But if you had a Volkswagen Polo the front would be 33 PSI and rear 31 PSI as the manual explains.

Checking your current tyre pressure

Once you know your vehicle load, using your gloves (if you prefer not getting grime all over your finger) unscrew the dust cap from the valve. Once removed place it somewhere safe as they often have a habit of going missing. The next step is to push your digital or analogue car tyre pressure gauge against the valve. Hold it there for a few seconds to get a good, accurate reading. 

Note: Checking your car tyre pressure after it's been out in the sun for a long period will produce DIFFERENT results compared to checking when the tyres haven't been heated up. Therefore we would suggest against checking the tyres when they're hot, as it's possible to pump the tyres up accidentally too far beyond the cold PSI reading.

If you're happy with the current reading then just give the valve a wipe with a towel to get rid of any dirt and screw on the dust cap. Be careful not to cross thread when doing this by ensuring the dust cap is centred correctly. If you aren't happy then it's time to change the pressures.

Reducing car tyre pressure

To do this simply place your BAR/PSI reader gauge into the valve as if you were checking the reading, but this time apply less pressure. As the inner valve is pressed down it will begin to let the air out of the tyre, you will be able to tell by the loud hissing noise as the air escapes. Be sure to stop every 5 or so seconds to recheck the proper reading, as it will fall very quickly when letting air out. 

Increasing car tyre air pressure

Attach your pump valve cap to the tyres air valve cap and begin adding air. Make sure to stop every so often to check to see if you're getting near the desired PSI reading. Remember, this is best done in the early morning before the sun warms up your tyre (especially in Summer) so that you aren't given a false reading. 

Once you're all sorted with either reducing or increasing the air pressure inside the tyres, screw the dust cap back on being careful not to make it too tight, otherwise you run the risk of cross-threading. And you're all done! Note down when you performed the check so that you can check once a month on the same day. Personally, I check my tyres every 2 weeks Sunday but I drive a lot so this may be a bit much for most people! Once a month is fine in any case.

Quick Tyre Pressure Tips

• Always give your tyres a check over to look for structural damage before pumping more air into them
• Tyres MUST be cold before getting a reading or removing/adding air otherwise you will get false readings from hot tyres
• Schedule a date for checking your car tyre pressure, either every 2 weeks or monthly
• Make sure to find the CORRECT car tyre pressure by looking in an official manual specific to your vehicle
• Make sure to update the pressure settings based off whether you'll be travelling alone or with a fully laden car
• Make sure to get a reading on your spare tyre if you have one
• Use a digital pressure gauge for the most accurate reading, but an analogue one will do just fine
• Wear gloves when you are dealing with dirty tyres, this saves you from getting grime all over your hands

Conclusion

With the entire weight of your vehicle being held up by your car tyre pressure, it's imperative that they receive regular checks to ensure the safety of your car. Remember to set a schedule for checking your tyres as they lose air slowly over time, so one day you will find yourself with under-inflated tyres if you don't keep an eye on them. 

Stable Vehicle Contracts is a performance car leasing and contract hire company situated in Liverpool, UK. We deliver cars anywhere within the UK + Northern Ireland. You can check our stock list here. Alternatively, pick up the phone and give us a call on 0151 728 4711 or submit a form via our contact us page.