Tyre Pressure


Tyre pressure

Correct tyre pressure can help to extend the life of your tyre, improve vehicle safety and maintain fuel efficiency. Pressure is measured by calculating the amount of air that has been pumped into the inner lining of your tyre in pounds force(PSI) or BAR pressure.

The manufacturer of your vehicle specifies the suitable pressure, and it is your responsibility to make sure that the pressure is checked and corrected on a regular basis, at least every couple of weeks.

Maintaining correct Tyre Pressures

There are three main reasons why maintaining the right tyre pressure is important. The first is safety. Tyres that are under inflated can overheat; and over inflated tyres can lead to poor vehicle handling on the road.

The second reason is economy. Over or under inflated tyres suffer more damage than those with the correct pressure and need to be replaced more regularly. Vehicles with under-inflated tyres have increased rolling resistance that require more fuel to maintain the same speed.

The third reason for maintaining the correct tyre pressure is the environment. Correct tyre pressures help to maintain optimum fuel efficiency. This can equate to lower Co2 emissions coming from your vehicle than those with incorrect tyre pressures and that has to be good for the environment.

It’s important to check tyre pressure regularly. It’s not always apparent that air is being lost, but it generally escapes at the rate of up to two pounds of air every month. More air is usually lost during warm weather, so more regular checks are needed when temperatures rise.

Look for the tyre pressure recommended for your vehicle in your vehicle hand book or within the technical information usually found on the inside of your vehicle‘s front right hand door or fuel tank flap.

Always check the tyre pressure with a tyre pressure gauge when your tyres are cold. Finally, if you are using your vehicle to carry additional load or weight, always consult your vehicle handbook for the correct loaded tyre pressure.

How to check your tyre pressure and wear levels

Please note that this is only a general guide and is not specific to any one make or model of vehicle. For more detailed information on your own particular car, please consult a workshop manual specific to your own make and model!

Read this first : If you have recently driven your vehicle, please leave it for at least an hour for the engine and other components to cool down. If you do not you may risk injury!

Required Tools:

1. Tyre tread depth gauge (not essential, but useful)
2. Tyre pressure gauge (not essential but again handy to have. If you do not have one your local garage should have a public use air compressor with a pressure gauge)
3. Small compressor/inflator (see bracketed section above)
4. A small flat head screwdriver (if you find any nails stuck in your tyre)
5. A small cup of water and some washing up liquid (to check for air leaks)

Step 1 – Access the tyre tread

In order to accurately check your tyres for wear and damage you need a good view of them. Position your car on a flat and level surface.
Once you are satisfied with this apply the handbrake and put it into park (for automatics) or first gear (for manuals). Now turn the steering roughly 45° left or right (depending on which side of the car your working).

You now have a decent view of your desired tyre and can begin the inspection.
NOTE: You should always check your tyre pressures when the tyres are cold. Under driving conditions the tyres will warm up and give you a false reading so if you have driven further than roughly a mile leave your car for an hour or so for the tyres to cool down.

Step 2 – Check the tread

With a decent view of your chosen tyre you can now check the condition of the tread and the tyre itself. If you have a tyre depth gauge pop in into the tread in the centre of the tyre and observe the reading.

In terms of the law the legal limit for tread wear on a tyre is 1.6mm of tread left in the centre 3/4 of the tyre, but this is the limit! Ideally you would want to be changing your tyres at about 3mm.
If you don’t have a tyre tread depth gauge then the majority of new tyres have their own built in. In between the treads of the tyre you should be able to see small blocks of rubber roughly half the actual depth of the tread. These are the tread wear indicators and if you find that your tyre treads are level with these little blocks, get your tyre(s) changed immediately, they are below the legal limit!
Another trick is to use a 10 pence piece. If you put the coin down into the tread it should cover the dotted rim just around the inside of the coin. If not your tyres are below the legal limit.

If, on inspection, you have found that only certain section of tread appear to be worn, this can be for several different reasons:-

Both edges of the tyre are worn This could signify under inflation. Check your tyre pressure (see step 4)
Centre of the tread is worn This could signify over inflation. Using a pressure gauge (see step 5)
Worn on one side only Your wheels may be poorly aligned. Take your car to a garage or tyre centre and have them check your tracking
Whining, clunking and other noises Your wheels may be poorly aligned or you have worn shocks or tyres
Scuffs on edge of front tyres You may be driving and cornering too fast! Slow down.
Treads worn unevenly Your wheel balancing and/or tracking may be out. Take your car to a garage or tyre centre and have your tracking and balancing checked.
Unevenly spaced bald spots Your wheel balancing may be out or your shock absorbers are worn. Take your car to a garage or tyre centre and have them check this out!

Step 3 – Check for damage

The next job, once you have checked the tread, is to check the general overall condition of the rest of the tyre for any other damage. It should be possible for you to view the entire tyre by simply turning the steering wheel to the left or right (depending on which area of the tyre you want to view) but if you are not satisfied with the view that this gives, you may find it easier to remove the whole wheel and inspect it off the car.
When inspecting a tyre for damage you should be looking out for cracks in the tyre wall (this usually signifies an old tyre as the rubber is beginning to harden and perish. Also, if you haven’t driven your car for a long period of time and it has been sat in one place this can also cause a tyres’ walls to crack), bulging in the tyre wall (this could be the result of the tyre colliding with something such as a kerb or pot hole and this has weakened the tyre wall) and deep cuts or gouges (these should be quite evident. Likely causes for this could again be collisions with objects such as kerbs, pot holes or road debris).
In the event that you do find any of the above change this wheel immediately! Swap it for your spare (see NOTE: above for instructions) or get to a garage/tyre centre.
You should also inspect the tyre for objects embedded in the tread. The majority of the time this will probably be gravel but you may find pieces of glass and some times even nails.
In the event that you do find a nail in your tyre, before you attempt to remove it, make sure you have a spare and it is useable.
Take your flat head screwdriver and push the tip under the head of the nail and slowly prise it up. If you hear a hissing sound then the nail has gone right through so push it back in and swap this wheel for your spare or get to a garage/tyre centre and get it fixed (in this case it may not be necessary to replace the tyre you may be able to have it patched. Ask a professional for their advice). If its only a short nail then it may not have penetrated the tyre completely.
If it’s only a very slight hole then you may not be able to hear the air escaping. To make sure of this a little tip is to get some water and add a small amount of washing up liquid and then apply it to the hole. If it bubbles up then there is air escaping so change the wheel or get the tyre repaired.

Step 4 – Check your tyre pressure

An under or over inflated tyre can affect several aspects of your motoring. It can seriously reduce its life span, lower the fuel efficiency of your car and effect your cars road handling and braking.

The easiest and most cost effective method of checking your pressures is to use the public air compressor that you should find at your local petrol station. Along with this there should also be a chart on the wall with information about tyre pressures for the majority UK makes and models. If not, the correct pressures for your own car should be in the vehicles user manual.
NOTE: Make sure that you have the correct pressures in the front and rear tyres of your car. Many modern vehicles tyre pressures will differ between the front and the rear.
You may be lucky enough to have your own tyre pressure gauge and compressor. If so you can check your pressures from home just make sure you know what pressures should be in each tyre.

Step 5 – The valve

Another vital part of any tyre is the valve. This is the part that you would connect the end of an air compressor to to pump up a tyre. Like the tyre itself, valves can also wear out or become faulty. If you have found that your tyre slowly deflates despite that fact that you have checked it and have found no damage, then it is most likely to be the valve.
The main failings with a valve could either be the valve stem (the rubber body of the valve that sits in the rim of the wheel) or the valve itself (the tiny pin-looking object that sits in the valve stem).

To check your valve for leaks firstly bend the valve stem from side to side and back to front (make sure you do this gently as you could end up damaging it when it is really ok) and look for splits in the rubber. If this appears to be fine then check the valve itself. If there is a split in the rubber then you will have to get this replaced. Visit your local garage/tyre centre and have a professional carry out the work.
Remove the dust cap from the top of the valve stem (the small screw on cap). Using the soapy water mixture mentioned in the final paragraph of Step 3 apply a small amount to the top of the valve. If it bubbles up then you have a leak (remember to re-fit the dust cap as this will prevent dirt and moisture from interfering with the valve. If there wasn’t one on the valve in the first place purchase a set from your local motor spares store, they cost next to nothing).
It is possible to replace the valve your self by purchasing a valve removal tool and a replacement valve but be aware you will lose the majority of air in the tyre. If your not sure on how to do this yourself have an expert carry out the work for you.

Step 6 – Removing air from a tyre

If, on checking your tyre pressures, you have found that one or more are over inflated then you should take some air out (check your vehicle user manual for exact pressures per wheel).
Before you begin this task make sure you have a compressor to hand. If you have one of your own, that’s great. If not, visit your local garage (you will need to be able to check how much air you have in your tyre and also replace it if you let out too much)

To do this remove the dust cap and expose the valve. If you have any finger nails push down on the pin-looking point in the centre. If you don’t have any nails then use a flat head screwdriver.
If you are doing this correctly you should hear a “hissing” as the air comes rushing out (do not let out huge amounts at a time, only a little and also check with the pressure gauge on the compressor each time until you reach the desired pressure for that particular tyre).

NOTE: Your tyres are extremely important to the efficiency of your car and also your own health! If you have found any damage or wear make sure you get the tyre repaired or replaced as soon as possible.


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