Tyre pressures? I’ll do that next week!
Like so many simple car maintenance jobs we should do as a matter of course, tyre checks always just seem to fall by the wayside. Walking up to our car as we do these days, pressing a button on a remote key phob and jumping in to join the maelstrom of modern life when would we ever have a chance to do this? Stopping to check the tyres just seems like a pain in the proverbial. Procrastinated by a day that somehow just morphs into a year, we really do give our tyres some inexcusable abuse.
“Sure I’ll feel something odd or different if there is something wrong?” This may have worked in your Dad’s day when he drove a 1970’s ford escort or Datsun 120Y but things have changed. The environment in today’s cars is more like a plush lounge with soft furnishings and acoustic isolation we take for granted. After all this is the luxury we have paid for. Then we consider modern vehicle suspension systems with computer designed damping which actually achieves the impossible, taking any concept of the work our tyres do clean out of our minds. Finally the chassis engineering that is behind our modern steering systems. Load sensitive power steering, electronic power steering often with active damping and the result? We could almost drive with no tyre at all fitted on one corner of the car and hardly know a thing about it!
There is incentive to check our tyres beyond our own and other’s safety too. It will hit you in the pocket if you neglect your tyres. Over or under inflation of our tyres, given all of the engineering the car maker has invested in your comfort will result in accelerated wear on a massive scale. The tyre does an awful lot of work so when it is compromised by being operated outside its ideal conditions it is hopelessly incapable of doing its job. It suffers and it suffers badly. Have a look at the illustration below.
Totally aside from comfort and safety due to a compromised tyre contact area, the physical distortion of the tyre through over inflation or under the weight of the car when under inflated will cause accelerated wear. As you can see from the diagram above in the case of over inflation there will be a “crown” in the centre of the tyre contact area which will wear doubly fast as it bears too much weight over too small an area and of course, reduces wear considerably on the remainder of the tyre which hardly touches the road. Conversely when under inflated, the outer portions of the tyre tread which are supported by the side walls will support the weight of the car and driving loads while the centre of the tyre tread will just deform away from the road, with insufficient pressure forcing it down against the road surface.
So how does one check tyre pressure? Step one will be to establish what the correct pressure should be. Most car models make life very easy for us but in the same way we can procrastinate the tyre check in the first place we can easily fail to notice the sticker. This will usually be found inside the fuel filler cap cover or visible in the driver’s door opening when the door is open. Not only will most manufacturers put the inflation pressures here but they will normally advise if there is a different pressure required for lightly or heavily loaded conditions so look closely.
How will the pressure be quoted? This is a miles vs kilometres thing and in most cases the label just like the gauge on the garage air-line will be marked in BAR and PSI. If you understand kilo-pascals, pounds per square inch and millibars, then you should feel a nice comfort come over you now, this job will be simple. If not, well fear not! Establish the pressure in whatever scale you will remember easiest and stick to this plan.
Once at the forecourt nothing could be easier. If the air supply is an automated pumping system then use the controls on the console to adjust the pressure setting to whatever you read from the inflation chart on your car. Walk over to the tyre you are checking, remove the screw-on dust protection cap over the inflation valve and press the air line firmly up against the valve. Wait until the pulsing and hissing ends, you will hear a beep or similar to tell you that you are done as this machine will inflate or deflate your tyre to whatever value you tell it to. If on the other hand the air line is of the older type with a gauge and trigger then it is different but not difficult. Bring the air line to your tyre, remove the dust cap from the tyre’s inflation valve. Press the air line firmly against the tyre valve and look at the gauge. The pressure will be reported on the gauge so it will be up to you to decide now if you need more or less air in the tyre. Either is possible and equally simple. For more pressure pull the trigger as far as it will go for one to two seconds, release the lever and check to see what the gauge is reporting now. It will not only tell you how much air is in the tyre but it will also give you an idea of how fast you are inflating the tyre. Use your best judgement to know how much additional pressure to add or not. If you have too much air in the tyre or if you add too much, fear not either. Pull the trigger gently and it serves as a pressure release valve. Similarly to filling the tyre, let air out in one to two second shots and check the gauge as you do.
Now that is a pretty comprehensive summary of all that is involved in checking tyre pressure and probably serves to comfort you further with all the talk of modern suspension and steering and cozy passenger compartments so time for the scare! Yes, the combination of modern car technology and neglect of your tyre pressure is patently dangerous, possibly more so than in the old days of that Ford Escort or Datsun 120Y. Your car will almost certainly have anti-lock brake systems and possibly a vehicle stability program which you will pay equally little attention to. These systems are superb additions to a car and can critically stabilise your car during an emergency scenario. They operate like all software based systems on assumptions as they have to. One of these assumptions is that each of your tyres is producing adequate friction with the road and roughly equal friction to the other tyre on the same axle. Distort this equilibrium and the result will be both shocking and possibly horrendous. Braking distance with poorly balanced tyre pressures can be greater than without electronic aids so pay attention! Consider it like a short-odds bet, take the time to check your tyres and do it soon. Be sure to remember this scare story very often, we suggest at least once a month and spend five minutes checking your tyres.