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February 2002 Newsletter
Tire Pressure
Over the last year we have recommended an increase in tire
pressure as a maintenance tip for increasing gas mileage. Many readers
have scoffed at this recommendation and called it dangerous and reckless.
Many times I have personally defended this position and continued to be faced
with the issue so I have decided to write this article so readers can reference
it when they have complaints about my recommendations.
I repeat my recommendation, “increasing tire pressure to 50
psi will improve your gas mileage. It will, however, cause a rougher ride
if you drive on rough roads.”
The following are some informative excerpts from the
referenced web pages that concern tire safety. You will notice from these
passages that unsafe tire pressure is much more critical for tires that are
under-inflated than for those that are over-inflated. I will discuss this
statement at the end of this article. Please review the following
excerpts:
http://money.cnn.com/pf/autos/features/safety/page2.html
2. How safe are your tires?
by Jerry Edgerton
Tires that don't have enough air can kill you
Under-inflated tires flex too much and build up heat, which can lead to
blowouts and tread separation, where the tread peels away from the body of the
tire. Tread separation set off the Firestone tire recall and the company's
dispute with Ford over who is responsible for the more than 100 deaths blamed
on tire failures and Explorer rollovers.
As the companies have traded charges, drivers have been left with this
question: How low is too low?
The answer: Just four or five pounds per square inch (PSI) too low can be
dangerous, tire safety experts say. With such a narrow margin for safety, it's
important to check your air pressure at least monthly. But don't rely on
the recommended pressure noted on the tires themselves. Instead, auto safety
experts agree that you should follow your car maker's pressure
recommendation. Car makers usually post it on a metal plaque on the driver's
side door pillar or inside the glove compartment. It may also be in the owner's
manual. On European brands, it may be inside the gas-cap cover.
I know that the appropriate pressure has been the main issue in the Firestone
and Ford dispute. Firestone contends that the Explorer tires needed 30 pounds
per square inch to perform effectively, while Ford recommended that the
tires run at 26 PSI, which Firestone says is unsafe. Such a wide
disparity is very unusual, and that's why in almost all cases I recommend
you follow the automaker's tire pressure number. After all, I think the
car maker is in the best position to know how your model will run best.
Check your tire pressure
As for how you check your pressure, be wary of gauges at service
stations, since their readings are often inaccurate and inconsistent. I'd
recommend that you simply buy your own tire gauge at an auto-parts store
(it should cost no more than $5 or so). Test the pressure of each of the
tires when they are "cold," before the car has been driven. If
you must add or subtract air, always retest the tires with the gauge
afterward to get an accurate reading.
Heavy-load alert
Tires are often weakened by the stress of hauling gear or by towing a
boat or trailer, especially if you are driving for long periods at speeds
over 65 mph. This can heat up the tires and cause them to blow out.
You may think that it helps to let air out of your tires as a precaution
during these situations. But, in fact, the opposite is true. To make sure your
tires hold up under heavy loads, you may actually need to add an additional
five pounds per square inch to each tire, says John Rastetter, director of tire
information for Tirerack.com, an online tire seller. Consult your owner's
manual for the heavy-load pressure recommendation.
Danger signs
If when driving at highway speeds you hear a muffled thumping noise or feel a
shimmy in your steering wheel, it may be a sign of trouble. The noise may
indicate tire tread problems that require immediate attention. The shimmy may
mean your wheels are out of alignment, which can cause tires to wear
prematurely.
Maintenance
Get a jump on tire problems by checking their condition every six months.
Stick a penny into the tread. If the tread does not reach the top of Lincoln's
head, you need new tires. Keep in mind that most tires usually last 40,000
miles, and it's prudent to have a mechanic check your alignment every 5,000 to
7,000 miles.
Ratings count
It's not just cars that are rated for safety. In addition to doing extensive
crash tests on all models, the government rates all tires that are on the
market. The ratings are generally noted on the side of a tire -- A is the best,
C is lowest -- and you can also check the website of the National Highway
Traffic Safety Administration, or NHTSA. If you drive long periods at high
speeds or with heavy loads, you should have tires rated B or better for
resistance to heat. For instance, the Firestone Wilderness AT, one of the sport
utility tires involved in the recall, gets only a C rating for heat resistance.
Competitor Goodyear Wrangler gets a B and costs no more (about $100 per tire,
installed).
http://www.mastercare-usa.com/tires/warranty/warr7.htm
Driving on tires with too little air pressure is dangerous. Your tires will get
overheated. This can cause a sudden tire failure that could lead to serious
personal injury or death. Under inflation may also:
1.damage the tire leading to tire failure.
2.adversely affect vehicle handling.
3.reduce tire life.
4.increase fuel consumption.
Driving on tires with too much air can be dangerous. The tires are more
likely to be cut, punctured, or broken by sudden impact. Serious personal
injury or death could result. Consult your vehicle’s tire placard for the
recommended inflation and your owner’s manual for other tire information.
Tips For Safe Tire Inflation
Check your tire air pressure, including
your spare tire, at least once a week and before long trips. Be sure to use an
accurate pressure gauge.
Check your air pressure when the tires are
"cold." The tires are cold when your vehicle has been less than a
mile at moderate speed or after being stopped for three or more hours.
If you must add air when your tires are
hot, add four pounds per square inch (psi)(28kPa) above the recommended cold
air pressure. Recheck the inflation pressure when the tire is cold.
Never release air from a hot tire in order
to reach the recommended cold tire pressure.
Normal driving causes tires to run hotter
and air pressure to increase. If you release air when your tires are hot, you
may dangerously under-inflate your tires.
If your tires lose more than two pounds
per square inch (2 psi)(14kPa) per month, the tire, the valve, or wheel may be
damaged. Consult THE DEALER location for an inspection.
Check your spare tire. Consult your
vehicle owner’s manual for the correct inflation and use of a “temporary use”
spare tire.
Use valve caps to keep valve cores clean,
clear of debris and to help guard against air leakage.
3.LT (Light Truck) Designated Tires Only. It is not recommended that your truck
be operated at speeds in excess of legal limits. However, if it is anticipated
that sustained
driving speeds in excess of 65 mph may be required, then:
(a) At speeds from 66 mph through 75
mph (106km/h through121 km/h), cold inflation pressures must be increased 10
psi (70 kPa) above the recommended pressure for the load being carried. Do not
exceed the maximum inflation pressure of the wheel.
Sustained speeds from 66 mph through 75
mph are not permitted when the 10 psi increase would exceed the wheel’s maximum
inflation pressure.
(b) For sustained driving at speeds from
76 mph through 85 mph (122 km/h through 137 km/h), reduce axle load capacity by
10% in addition to increasing the cold inflation pressure by 10 psi above
recommended pressures as listed in (a) above.
http://www.metropark.com/safewaytire/air.html
Air Pressure
Tires support the weight of your
car, right ? Actually, they don't. The air pressure inside the tire is what
supports the car. The tire is basically just a container to put the air
in. The correct air pressure is required for good handling, traction and
durability.
However, you can't just set it and
forget it. In most parts of North America, fall and early winter months are the
most critical times to check inflation pressures because the days are getting
shorter and the temperatures are getting colder.
And since air is a gas, it contracts
when cooled, for every 10 degrees Fahrenheit change in ambient temperature,
your tire's inflation pressure will change by about 1
psi. It will go down with lower temps, and up with higher temps. The typical
difference between summer and winter temperatures, is about 50 degrees F. -
which results in a loss of about 5 psi and will sacrifice handling, traction,
durability, fun, and safety.
The tire pressure recommended in your vehicles owners manual or tire
information sticker is a "cold" pressure, so it should be checked in
the morning before you drive the car more than a few miles. And by the way, if
you park in a heated or attached garage, you will "lose" pressure
when you leave its warmth and venture out into the cold. You may want to add 1
psi for each 10 degree F. in difference to compensate.
Keep in mind that tires tend to lose about 1 psi per month, so check them
often.
End of excerpts.
Discussion:
Earlier I made the statement that “unsafe tire pressure is much more critical
for tires that are under-inflated than for those that are over-inflated.”
Let us look at some quotes from the above excerpts.
“Tires that don't have enough air can kill you”
“Just four or five pounds per square inch (PSI) too low can be dangerous”
“Firestone contends that the Explorer tires needed 30 pounds per square inch to
perform effectively, while Ford recommended that the tires run at 26 PSI,
which Firestone says is unsafe.”
“You may think that it helps to let air out of your tires as a precaution
during these situations. But, in fact, the opposite is true. To make sure your
tires hold up under heavy loads, you may actually need to add an additional
five pounds per square inch to each tire.”
“At speeds from 66 mph through 75 mph (106km/h through121 km/h), cold inflation
pressures must be increased 10 psi.”
“Driving on tires with too little air pressure is dangerous. Your tires will
get overheated. This can cause a sudden tire failure that could lead to serious
personal injury or death.”
“Check your air pressure when the tires are "cold." The tires are
cold when your vehicle has been less than a mile at moderate speed or after
being stopped for three or more hours. If you must add air when your
tires are hot, add four pounds per square inch (psi)(28kPa) above the
recommended cold air pressure.”
“Normal driving causes tires to run hotter and air pressure to increase. If you
release air when your tires are hot, you may dangerously under-inflate your
tires.”
“For every 10 degrees Fahrenheit change in ambient temperature, your tire's
inflation pressure will change by about 1 psi.”
“A loss of about 5 psi and will sacrifice handling, traction, durability, fun,
and safety.”
“Keep in mind that tires tend to lose about 1 psi per month, so check them
often.”
Now that’s a lot of warnings about under-inflated tires and rightly so.
When tires are under-inflated the sidewalls are bent and distorted and thereby
weakened. This excess bending and distortion also causes heat build up in
the rubber compound, which softens the compound and eventually breaks it
down. Under-inflated tires are indeed dangerous, yet how many under-inflated
tires do you see every day? How often do you check your tire
pressure? When you do check your tire pressure, how often do you find the
pressure at least four psi lower than the recommended pressure? “Unsafe,”
say the experts.
Now let’s do some mathematical calculations on some possible situations.
Let’s take a typical winter situation here in upstate New York. In one
week the temperature can vary from –30 degrees to positive 60 degrees.
That’s a difference of 90 degrees Fahrenheit. According to the article
that means a difference in tire pressure of 9 psi. I confirmed this
calculation by the ideal gas law and it is accurate. Now if a decrease of
tire pressure of 4-5 psi can cause damage, I certainly wouldn’t want to check
my pressure on a 60 degree day and then drive my car on that –30 degree morning
because the tire pressure would be about 9 degrees under-inflated. Of
course the standard is that the recommended tire pressure is a cold inflation
pressure, which in my case would be on that –30 degree morning. This
would mean that on the 60 degree day the tire pressure of that same vehicle
(inflated properly) would be 9 psi higher than on the cold morning when it was
checked (32+9=41 psi). Now when you start driving that car the tires heat
up even more. How much they warm up is dependent upon the load being
carried, the speed being driven, and the makeup of the tire itself. I
would estimate that the tire temperature (and therefore the air inside that
tire) will increase another 20 to 50 degrees. Certainly on a sunny road
and aggressive driving this is not an unreasonable expectation. So if we
add the 2-5 psi caused by this tire warming to the 9 psi caused by the ambient
temperature change, you have a total of 11-14 psi increase over the 32 psi
recommended tire pressure for all of my cars. That would by itself cause
a tire pressure of 43-46 psi.
In reality the standards for setting maximum recommended tire pressures for
tires include the worst possible conditions like the following: Take a
car at –40 degrees and inflate the tire to the recommended 32 psi, then take
that car to the hottest day of the year in the hottest likely environment, say
Gila Bend, Arizona in the summer (125 degrees ambient and 150 degrees at the
road surface), then drive that car 120 mile per hour on a relatively rough
surface (causing the tire temperature to rise to 200 degrees), then engineer
into the tire a 50% safety factor over the stresses it would encounter by
hitting a pot hole at that high speed, after being worn down to the point that
all the tread is worn off. This would mean that the tire pressure would
be 32+23= 55 psi inside that hot tire which is weakened by the extra heat from
the excessive speed and road roughness. Now that tire still has a 50% safety
factor engineered into the strength of the sidewalls.
Now let’s take that tire back to my regular driving conditions at my
recommended tire pressure. First of all there is no place within one mile
of my house (and likely yours) to fill up my tires. I have to drive a few
miles to get to the available compressed air, so my tires are checked when my
tires are warm. I use 50 psi and when I get home to that cold morning,
the pressure is down to a safe 40 psi or less instead of the unsafe 24 psi that
most tires will have. I don’t drive on excessively rough roads at
excessively high speeds and since my tires are flexing less because they have
plenty of air pressure in then, they don’t flex and bend and distort as much as
an under-inflated tire. So they don’t cause an extra 50 degrees of
temperature and thus an extra 5 psi of pressure. Also because of the lack
of excessive speed, I won’t be hitting a pothole at 120 mph so I won’t worry
about that event.
Am I driving an unsafe vehicle because I drive with 50 psi (warm)? I
don’t think so. Are most people who don’t check their tire pressure
often, driving on unsafe tires? If they are typical they have at least
one tire on their car that has less than 25 psi which is way under what Firestone
says is safe. I would be willing to bet that if you went on a cold
morning to a local business parking lot and checked tire pressures, you would
find at least one tire on at least half the cars that was under-inflated to the
point that it was “unsafe.” In fact if the following quote is true,
and you haven’t checked your tire pressures in 4 month, you have unsafe tires
on your car.
“Keep in mind that tires tend to lose about 1 psi per month, so check them
often.”
Over-inflation (within the limits of my recommendations) is not the safety
problem with most tires, under-inflation is. The excessive number of
accidents caused by under-inflated tires in recent years, is evidence of this
opinion. Tire manufacturers, auto companies, and victim’s families are
paying dearly for the lack of knowledge by the general public concerning safe
tire pressures. 50 psi (warm) is not unsafe, 25 psi is.
Another Competitor Listed on Web Site
At the Hydrogen-Boost web site, we attempt to give the
visitors access to as much information about our competitors as possible.
On our Technical Information page of the web site we provide links to our
competitors’ web sites. Recently we have discovered another competitor,
Dynamic Fuel Systems Inc. and their product, the Hydrogen Power System, which
is a rather cumbersome hydrogen generator, designed to be mounted outside on
large diesel trucks. After reviewing this web site and others marketing
hydrogen generators for diesel applications, I am beginning to withdraw my
reservations about the benefits of adding hydrogen to the intake air of a
diesel engine. I do have data on the effects of Hydrogen-Boost on the
emissions of a diesel engine. Though I don’t have any personal
comprehensive experimental data on the effects on mileage, I will now encourage
those with diesel engines to explore the benefits of the whole Hydrogen-Boost
system, including the hydrogen generator.
Subscriber Comments
Opinions and information reported in this section are those of our readers and
are not verified by us. We do not stand behind any claims made in this
section of our newsletter.
Great newsletter. I was informed by a Dr. Bamber of Lewis and Clark
Community College in Godfrey IL informed me that all fuels are 93 octane.
Read the yellow label at the pump. It guarantees a minimum rating of 87 or
whatever fuel selected. Now it is against the law to sell 87 as 93. It is
not against the law to sell 93 as 87. The oil companies manufacture all of
the fuel at 93 to cut costs of having to make 3 different grades of fuel.
This info was passed on to the good Dr. Bamber by a student who was a Shell
Oil employee. In addition, in areas where the companies do not sell or ship
their brands; they buy competitors and use it for resale under their company
name. Be Blessed.
Hi Fran
Thanks for your latest news letter.
I am a (now inactive) member of supercarbs and have been using fuel line
magnets on a fuel-injected vehicle for several years now. My opinion is now
that the magnets do cause slightly more efficient burning of the fuel,
resulting in slightly more oxygen in the exhaust. The fuel injection
computer then increases the amount of fuel being injected, which in my case
produces a noticeable increase in power and low down pull but no real
improvement in MPG. But the power improvement is welcome in my underpowered
1.3L motor.
For some time I deluded myself into thinking I was getting better MPG, but I
have decided that this was only a sort of placebo effect - while I was
looking for improved MPG I drove more carefully!!
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