A Public Safety Notice
A lady came into the Motor Project this afternoon to ask if anyone had seen her son's toy scooter that she had accidentally left on the pavement outside earlier in the day. One of our students said he had seen it earlier but didn't know what had happened to it, and by the way did she know her tyres were flat? She said she would go to the garage and check them, but he offered to check them for her, which she reluctantly accepted. It turned out she was driving around on some severely under inflated tyres - one of them was at 8 psi when it should have been 26 psi! To make it worse she had a small child and a little baby in the car. I guess that, like a lot of people, she didn't know the possible consequences of driving on flat tyres. To be honest, I hadn't really thought about it much either before I started at the Motor Project.
For all those who had never really thought it through, the consequences can be serious - and here they are:
In the short term, you probably wouldn't notice a slight under inflation, but it will make your steering heavier and less predictable. This is bad because you never quite know how much you will need to turn the steering wheel to avoid an obstacle. It will also increase stopping distances, as the middle of the tyre pushes inwards and leaves only the shoulder area of the tread in contact with the road. This pushing in of the tread will of course also decrease grip in the wet. Both of these are a problem if you need to stop suddenly - if you don't see why that is bad, please never get behind the wheel of a car!
Did you know that a properly inflated car tyre (of average size) has a contact patch about half the area of an A4 sheet of paper? You rely on that small area to keep your car on the road, and to stop your car in an emergency. Anything that reduces the contact patch reduces your control, especially in wet or emergency conditions.
Of course, over inflation also reduces your contact patch since the tyre pushes out in the middle of the tread and will cause some of the same problems, but your steering will feel light and 'skittish' instead of heavy. Again, I shouldn't need to explain exactly why this is BAD...
In the long term though, under inflation can be worse than over inflation, as it can cause some serious structural damage to the tyre. If the tyre is flat enough for the rim to push on the sidewall, this can cause the layers of rubber that make up the sidewall to delaminate (peel apart slightly) causing a bulge. In the UK, a bulge in the sidewall makes the tyre illegal, and can result in 3 points on your licence and a £250 fine. This may seem excessive, but it is for a good reason, since the bulge points to a weak spot which is likely to cause a blowout. Not something you want to risk when driving on the motorway with a family in the car! If you notice that you (or someone you love/like/tolerate/know) have been driving on under inflated tyres for any length of time, I would strongly suggest you get your tyres checked for bulges. Unfortunately you can't easily do it yourself with the car on the ground, but the cost of a check is a small price to pay to prevent a possibly fatal blowout.
In summary, please check your tyres regularly. In safety terms, they are possibly the MOST important part of your car that you can easily check yourself. All you need to do is look in the owners handbook (or online if you no longer have it) to find out what the pressure should be, and make a habit of checking at a set time such as when you do your monthly shopping, when you check the oil or on a set date like the first weekend of the month; or at the very least before you drive any distance! Also be aware that filling station inflators are often rather inaccurate (they get dropped and driven over, so no surprise really), which is perhaps why the law (in the UK) will give you 10% leeway before imposing the standard 3 points + £250 fine per tyre, but tyre pressure gauges are cheap and easy to use, and even the very cheap ones are likely to be more accurate than the filling station ones unless you abuse them - a good investment, or even a crafty stocking filler idea?
Disclaimer: As much as I hate having to add a disclaimer, it should be obvious that the above is based on my own understanding of the problems and laws mentioned, and as such they may be inaccurate or incomplete. This post should not be used as a definitive source, but may be used in whole or part (with suitable referencing) by anyone with a similar purpose , as long as it is not for profit.
For all those who had never really thought it through, the consequences can be serious - and here they are:
In the short term, you probably wouldn't notice a slight under inflation, but it will make your steering heavier and less predictable. This is bad because you never quite know how much you will need to turn the steering wheel to avoid an obstacle. It will also increase stopping distances, as the middle of the tyre pushes inwards and leaves only the shoulder area of the tread in contact with the road. This pushing in of the tread will of course also decrease grip in the wet. Both of these are a problem if you need to stop suddenly - if you don't see why that is bad, please never get behind the wheel of a car!
Did you know that a properly inflated car tyre (of average size) has a contact patch about half the area of an A4 sheet of paper? You rely on that small area to keep your car on the road, and to stop your car in an emergency. Anything that reduces the contact patch reduces your control, especially in wet or emergency conditions.
Of course, over inflation also reduces your contact patch since the tyre pushes out in the middle of the tread and will cause some of the same problems, but your steering will feel light and 'skittish' instead of heavy. Again, I shouldn't need to explain exactly why this is BAD...
In the long term though, under inflation can be worse than over inflation, as it can cause some serious structural damage to the tyre. If the tyre is flat enough for the rim to push on the sidewall, this can cause the layers of rubber that make up the sidewall to delaminate (peel apart slightly) causing a bulge. In the UK, a bulge in the sidewall makes the tyre illegal, and can result in 3 points on your licence and a £250 fine. This may seem excessive, but it is for a good reason, since the bulge points to a weak spot which is likely to cause a blowout. Not something you want to risk when driving on the motorway with a family in the car! If you notice that you (or someone you love/like/tolerate/know) have been driving on under inflated tyres for any length of time, I would strongly suggest you get your tyres checked for bulges. Unfortunately you can't easily do it yourself with the car on the ground, but the cost of a check is a small price to pay to prevent a possibly fatal blowout.
In summary, please check your tyres regularly. In safety terms, they are possibly the MOST important part of your car that you can easily check yourself. All you need to do is look in the owners handbook (or online if you no longer have it) to find out what the pressure should be, and make a habit of checking at a set time such as when you do your monthly shopping, when you check the oil or on a set date like the first weekend of the month; or at the very least before you drive any distance! Also be aware that filling station inflators are often rather inaccurate (they get dropped and driven over, so no surprise really), which is perhaps why the law (in the UK) will give you 10% leeway before imposing the standard 3 points + £250 fine per tyre, but tyre pressure gauges are cheap and easy to use, and even the very cheap ones are likely to be more accurate than the filling station ones unless you abuse them - a good investment, or even a crafty stocking filler idea?
Disclaimer: As much as I hate having to add a disclaimer, it should be obvious that the above is based on my own understanding of the problems and laws mentioned, and as such they may be inaccurate or incomplete. This post should not be used as a definitive source, but may be used in whole or part (with suitable referencing) by anyone with a similar purpose , as long as it is not for profit.
posted by Kristy at 8:41 pm
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