February 2002 Newsletter
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:
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.
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.
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.
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.
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).
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.
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.
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.
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.
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
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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