Even on dull days, the shadows cast by a highway over-bridge is an excellent marker with which to check that your following distance is adequate.

Photograph copyright 2012 - All rights reserved






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When were your tires actually made? It is important!


Where can you find the correct pressure to use for your tires?


How often should you check your tire pressures?


How important is it to use the genuinely correct pressures?


Tread depth


What About Winter Tires? (not yet done)




When our instructors, at Advanced Drivers of America, ask each group of trainees "How often do you check your tire pressures?" far more than 90 percent of the answers we get give us cause for concern.  Occasionally, somebody will even say: "I never check my tire pressures. I let the shop do it when they service my car."  This answer shows a serious lack of understanding about how important and how life-threatening this matter can be. What is is even more bizarre is the fact that even tire companies between them give at least four very different answers to this question and clearly only one of those answers can actually be the safest advice.  


Before we get around to doing those periodic tire-pressure checks for safety, however, lets deal with something even more fundamental because first we have to buy good tires! 


The first obvious task is to select the correct type of tire for how, when and where you generally drive such as "all weather" or "off road" and there's more about that below, but there's another really crucial thing to do at the same time and that is to ask the staff at the tire shop what the age of each new tire actually is, before the tires are fitted to your vehicle!


This might be something you have never even heard about, but many tires actually have the date-of-manufacture printed in the details on the sidewall.  (See the photograph, right.)


The first two digits of the four-digit number (which is apparently always in a round-ended box) show the week in which the tire was made, so if the first two numbers are "01" it was made in Week 1, and if they are "52" it was made in Week 52 the final week of the year.  The second two digits represent the year in which the tire was made so, for example, "3210" would be Week 32 of year 2010.

The "4808" shows that this tire was made in Week 48 of 2008.

Copyright 2010, Eddie Wren.  All rights reserved.

The danger from buying old tires


The problem, and the potential danger, comes from the fact that as tires age they become weaker and more prone to deflate or even to burst.  Even as children we all discovered that after a few days the thin rubber of a balloon starts to perish and air leaks out, and it is the same principle with tires although the thicker rubber lasts quite well for years rather than just days.  The question is "how many years" and, according to everything we have read on the subject, the answer always seems to be six.  And yet it is not unheard of for unscrupulous stores to sell tires that are five or six years old before they are even pulled out of a vast warehouse to be fitted to some unsuspecting customer's vehicle.  The crucial point is that even though those aged tires still look perfectly new when they are bought, the age-related deterioration of the rubber has still taken place and so the only piece of vehicle-equipment that actually keeps your car running under control is in danger of both failing you and killing you.  Remember that unless we do high mileages we can reasonably expect new tires to last for two, three or even four years so there is no point whatsoever in buying tires that have less than the necessary number of years remaining before they reach their important and potentially deadly sixth birthday!


What IS the correct pressure to put in your tires?


So now let's go back to the information on the sidewalls of your tires.  It is surprising how many people believe this is where one can find out the correct pressure to put into the tires but it is important to read it correctly.  What it actually tells us is the maximum pressure at which a tire may ever be used, not the correct pressure for that tire on your particular type of vehicle.  (See photograph, left.) 


But it is actually the automaker, not the tire maker, which decides the correct pressure for your tires.  Why?  Because only the automaker can measure the dynamics that their vehicle will apply to the tires and only they that can therefore assess what is needed from the tires, specifically for that vehicle.


Naturally, the pressures decided by the automaker can be found in the drivers' manual, in the glove box, but this information is also to be found on a black and yellow plate on the driver's door post (only visible when the driver's door is open).  On European cars, incidentally, the same information is often found on a plate inside the little door that covers the fuel filler cap.

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The maximum pressure at which a tire may be used, not the "correct" pressure!

Copyright 2010, Eddie Wren.  All rights reserved.

How often should you check your tire pressures?


Surprisingly, tire makers' advice on this important topic seems to have more to do with national culture than it does with any "best practice" or factual pursuit of safety.  On the surface of it, that sounds like veiled criticism although it is not really meant to be; culture is an almost inescapable factor in road safety.  Yet the sad fact is that at least five major tire makers give us one bit of advice in Europe, an entirely different guideline in North America, and Australia can be different again.   


The set periods that are contained in this variable advice are:

  • Once a month;

  • Once every two weeks ("fortnight");

  • Once a week;

  • Every time a car is driven.

In addition, there is also some very valid advice to check tire pressures "before every long journey."


There you have it: at least five different bits of advice.  So which one is right in terms of maximum safety?


Well, on the basis that some people make several trips a day in their car, the advice to check "every time the car is driven" could get a bit ridiculous.


At the opposite extreme, "once a month" is seriously inadequate.


The best advice among the remaining options is once a week (with an additional check before any long trip).  But if you are a particularly safe person then feel free to check you tire pressures every day.



U.S. National Tire Safety Week

Survey Findings 2010

Only 17 percent of vehicles had four properly inflated tires.

55 percent of vehicles had at least one under inflated tire.

15 percent of vehicles had at least one tire under inflated by 8 pounds per square inch (psi).

20 percent of vehicles had at least one tire under inflated by 6 psi.

31 percent of vehicles had at least one tire under inflated by 4 psi.


Source: Rubber Manufacturers' Association



The reason that "once a week" is the best, reasonable advice for checking tire pressures is simple:  Any form of slow leak from a tire whether caused by a small nail or perhaps by a bit of grit in the valve will reduce the pressure by a potentially dangerous degree in much less than a week, let alone a month.  So why on earth would we want to risk putting ourselves in a potentially dangerous situation and remaining in that predicament by only checking the pressures once a month? 


If all of this seems like a tedious chore be happy about the advent of Tire Pressure Monitoring Systems [TPMS], more and more cars are now fitted with this device.  But tires still need to be carefully checked visually, just as often, for signs of damage plus cuts and bulges, any of which can lead to a blow out.


How important is it to have the correct pressure in your tires?


Under-inflated tires wear fast at the edges (a.k.a. the shoulders) of the tread pattern which means you will need new tires sooner.  But there's something worse: Under-inflated tires overheat, and overheated tires commonly do burst, and if this happens when you are traveling at speed, the potential for danger is clear.


If, on the other hand, a driver over-inflates the tires it is the central band of the tread pattern that wears fastest because the tire has bulged like an over-inflated balloon.  But because the tire is running only on the central band of tread, as opposed to the full width of the tread pattern, there is much less rubber in contact with the road and the result is less grip, especially when grip is most needed:  under hard braking.  So with over-inflated tires braking ability is reduced.


Tread Depth


The legal limit for tire tread depth in the USA is 3/32" and most people have heard of the trick where a one cent coin is pushed into the groove with the top of Lincoln's head going in first.  If the coin goes deep enough for some of Lincoln's hair to be hidden from view, the tire is legal but if all of the hair remains visible the tread is too worn and the tire is illegal.

And if the tires on your Mercedes or your Cadillac start to look like this, it

might be time to get new ones!  (Photo copyright 2010, Eddie Wren)

If, however, you often drive on very wet roads (think "Florida thunderstorms every afternoon in summer") or if winter is approaching and you may end up driving on soft or wet snow, 3/32" of tread is definitely not adequate for safety.  Remember that the key purpose of tread is to provide channels through which water on the road can escape from under the tire and therefore let the tire grip better.  Changing your tires sooner than you normally would may make you feel as though you are wasting money but that "additional cost" is a joke when compared to the value of your life and the lives of your loved ones.

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All contents including text, logos, artwork and photographs are copyright 2010 Advanced Drivers of America and/or Eddie Wren, unless stated otherwise.  Website last modified on 07-May-2012.