For most of us, a car is one of the most expensive purchases we’re ever going to make. So when you drive your shiny new toy out of the showroom, or even if you’ve purchased a second-hand vehicle, it’s important to take the time to look after it.
For one, tyre pressure needs to be checked regularly. If it’s not part of your regular car maintenance routine, you risk the safety of yourself and others, as well as damage to your vehicle.
The majority of service stations provide facilities to enable you to do this quickly and easily.
It’s a very simple process, but there are a few rules that need to be followed. Firstly, your tyres must be cold.
Heat causes air to expand, and if they’re too warm, you’ll get an inaccurate reading. The recommendations vary, but ideally you should choose a service station fewer than 2km away. You can also purchase an air pressure gauge from auto stores if you want to do this in your own garage or driveway.
Inside the driver’s side door is a placard that will show the front and rear tyre pressure recommendations. In some vehicles, the front and rear will be different. This number is the minimum PSI (pounds per square inch) suggested by the manufacturer.
Some tyres may also have a recommendation imprinted on them, if that figure is lower than the manufacturer’s suggestion then seek professional help.
Most passenger cars range between 27 and 32PSI, trucks and larger SUV’s are generally much higher.
Locate the valve stem cap (usually black or silver) and unscrew it. It’s the same concept as a bicycle tyre, the valve stem is a small tube positioned near the hubcap, less than a couple of centimetres long.
There’s only one loose end of an air pressure gauge, that’s the bit you’ll need to connect to the valve stem. Push it on firmly, if it’s not quite right you’ll hear hissing air escaping. Adjust the angle if necessary until it’s airtight.
Some service stations may have a digital gauge and you may need to hit a button for the reading to show, some will do it automatically. Use your common sense to figure it out. If it’s an old fashioned gauge, you’ll see your reading on the dial.
In this case the gauge is digital and I need to set the required air pressure – the machine automatically does the rest.
Check the reading and if its correct, move on to the next tyre.
If it’s low, add air until the gauge shows the correct air pressure.
If it’s high, release the air pressure gauge from the valve stem slightly until you hear air escaping. Release the desired amount of air then remove the gauge.
Don’t forget to replace the cap. The cap isn’t required to prevent air loss, but without it dirt and moisture can make its way down the stem and into the mechanism that does.
Though it’s best to stick to the manufacturer’s recommendation when it comes to tyre pressure, there are exceptions that require higher or lower levels of inflation.
For example, carrying extra weight or towing. If you’re loading up the cargo area or transporting a car full of adults, add around 3-4PSI to your rear tyres. Adjust the pressure back to the recommended PSI when you’re back to normal driving.
In Australia we rarely need to do this, but if you’re travelling at speeds of 120km/hr or more for more than an hour it can put extra strain on the tyres. Again you can add 4PSI to the minimum suggested by the manufacturer to account for the extenuating circumstances, even though heat will increase the pressure, this will help reduce tyre wear. Keep in mind though that you shouldn’t inflate normal passenger car tyres over 40PSI.
When it comes to 4WD-ing, the general rule of thumb is to decrease tyre pressure by 4-6PSI. There’s a lot of debate surrounding the exact amount, but it will vary from car to car, and will also be dependant on the type of terrain. The aim is to increase the surface contact area of the tyre for stability, and reduce the risk of punctures or tyre blow-outs.
When we’ve done driver training courses in the past, we’ve been told to inflate our tyres to 40PSI and advised it’s fine to run our tyres at a slightly higher pressure than recommended for our everyday driving.
The reasoning is that those extra pounds of air can offer better fuel economy and reduced tyre wear. But CarAdvice recommends sticking to the manufacturers recommendations.
The tyres and suspension have been calibrated to perform optimally at the suggested figure. Running your tyres slightly higher may compromise ride comfort, and even slightly affect the speedo. Any slight change in circumference can be a problem – see our article on Low Profile Tyres here for more.
Over inflating tyres creates a smaller area of contact with the road and can wear unevenly, can effect braking, handling, tyre noise and ride comfort. On the plus side, rolling resistance is reduced which could improve fuel consumption.
On the other hand, under inflated tyres have a larger contact area which can increase fuel consumption. Tyre wear will be affected, and the tyres will heat up faster because of increased friction. This will reduce your tyre life and can be dangerous when it comes to braking performance and poor handling ability.
If you inflate your tyres with nitrogen, you’ll need to top up far less often. But don’t use air, always refill with the same gas.
Nitrogen doesn’t heat up as quickly as air, and due to its chemical structure doesn’t leak as quickly.
The cons are it’s harder to come by and costs money to refill each tyre.
How often should I check my tyre pressure?
Tyre pressure should be checked once a fortnight, or at the least once a month.
Permeation is a process by which air is lost through a solid substance, it’s a scientifically proven fact, and you will lose air slowly from your tyres even if there’s not a puncture.
The weather also has an effect. If there’s a cold snap, the air pressure will be reduced so keep in mind you may need to top up. A change of 10 degrees can change the pressure by 1PSI.
Similarly, when summer arrives or there’s a heatwave, take the time to check.
Last but not least, don’t forget about your spare tyre. It’s no use if it’s flat too.