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When were your tires actually
made? It is
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?
What About Winter Tires? (not yet
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
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!
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
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,
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.
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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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?
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
periods that are contained in this variable advice are:
there is also some very valid advice to check tire pressures "before
every long journey."
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.
opposite extreme, "once a month" is seriously inadequate.
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
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
• 31 percent of vehicles had at least one tire under inflated by
Source: Rubber Manufacturers'
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.
important is it to have the correct pressure in your 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.
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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