ROCHESTER HILLS, Mich. (Aug. 4, 2003)—With summer finally here and the temperatures soaring, maintaining proper tire air pressure has never been more important.
Having the right pressure to carry the load is important all year long—even in sub-zero climates—but blast-furnace-like temperatures can create tire meltdown in no time if tires are run underinflated. That's why we see so much more tire debris on the highways in the summertime than any other time of the year.
Now, more than ever, for safe and efficient operations it is necessary that every vehicle's tires be properly maintained.
Anatomy of failure
Heat is generated inside of a tire through sidewall deformation and tire tread contact with the road. The lower the air pressure, the more a tire will deform or flex, resulting in an increase in tire temperature. Excessive tire temperature that is aided by high ambient temperatures will destroy a tire quickly.
Road call data collected by a national road service provider, FleetNet America L.L.C, suggest that on average a typical tractor-trailer will experience about 1.2 road calls per year related to tire failures, and about one road call per year is directly attributable to improperly inflated tires.
Tires are by far the leading cause of emergency road service calls. They accounted for 48.9 percent of FleetNet's calls in 2000 and 2001. FleetNet's data indicate that the average lost time due to a tire-related road call is about 2.55 hours and that the direct-billed costs are approximately $265. This is just what FleetNet bills for the service call. It does not include the cost of a new tire, driver delay time, lost revenue, lost customer goodwill or other penalties associated with late deliveries.
Add up the costs
As you can see, the real cost of a tire-related breakdown is much higher than the direct costs paid to the emergency road service company.
The average cost/revenue per mile to operate a combination vehicle is about $1.25 for most general freight over-the-road operations. When you consider the average speed to be 60 mph, then a 2.55-hour tire-related breakdown results in a reduction of 153 miles traveled and a total loss in revenue or cost, depending on how you look at it, of $191.
Now throw in the cost of a new tire at, let's say, $275 and that road service call just went up to $731. Hopefully there were no penalties involved in freight delivery, for if there were, these can really make you want to slit your wrists.
For example, time-sensitive freight carrier Falcon Transport Co. caters to the automotive industry with the just-in-time freight service it provides. However, should a factory line shut down due to a Falcon late freight delivery, it is penalized $10,000 for each minute the line is down. Ouch!
But the impact of improper air pressure doesn't end there.
A common rule of thumb is that a constant 20-percent underinflated condition will re-duce the life of a tire by 30 percent and 40-percent underinflation will reduce tire life by 50 percent.
Increased flexing due to underinflation causes heat buildup within the tire components, which fatigues the steel cords and causes them eventually to break. Excessive heat is also generated which eventually destroys the tire.
Treadwear also is affected by underinflation. A constant 20-percent underinflation will increase treadwear by 25 percent.
Why would underinflation affect treadwear since the tread is on the outside of the tire?
Well, underinflation causes a tire's footprint to change, which results in the tread rubbing unevenly against the pavement. The tread slips more when it contacts the ground and this accelerates treadwear.
Proper air pressure gives tires the right shape for slow, even wear.
Another down side of underinflation is its effect on fuel consumption. Increased flexing and the irregular footprint caused by underinflation increases rolling resistance. That leads to greater fuel consumption as more power is required to move the vehicle. In fact, for every 10 psi of underinflation there is a 0.5-percent reduction in fuel economy.
As you can easily see, maintaining tire air pressure is vital to the good health of a trucking company as well as for others who share the road—like you, your friends and family.
Tire debris is the cause for a multitude of complaints emanating from the general public. John Q. Public is frequently writing letters to the editor, his congressman, the National Highway Traffic Safety Administration and anyone else who will listen about this problem when a “road gator” comes in contact with his car. It is usually erroneously perceived as being a failed retreaded tire.
In two surveys made on roadside tire debris, it was found that retread failure accounted for only 5-8 percent of truck tire failures. However, 86-90 percent of the failures were directly attributable to underinflation!
So proper inflation maintenance is a must during the summer months. Some people get a little carried away with this idea. I'm frequently asked if they should deflate their tires when traveling to areas of higher altitudes, like to Denver or over the Rockies, and then re-inflate them when they return.
Although air pressure does change with altitude—about 2 psi from sea level to 5,000 feet—the changes are small and should not be a factor in air pressure maintenance programs.
Worrying about this is like drinking light beer until a girl gets prettier. It's just not worth the effort!
Develop a program
Instead of worrying about peripheral concerns, your fleet customers should be encouraged to adopt a standard air pressure maintenance program that is performed regularly.
The appropriate cold air pressure for the loaded vehicle should be chosen and maintained. Air pressure should be checked as frequently as possible.
New tires tend to expand and increase their volume during a certain initial break-in period. This decreases the internal air pressure, so frequent checking is recommended up to about 2,000 miles. Tire pressures should be checked in the cool of the morning before vehicles hit the road.
Never bleed air pressure from a hot tire. When it cools, the tire will be underinflated. Be sure that when adjusting air pressure, the truck has been parked for three to four hours. And of course, accurate tire gauges should be used to check pressures.
No one, despite many years of experience as a driver or technician, has ever been able to consistently and accurately gauge tire inflation pressure using ballpeen hammers, “Tire Billys” or pointy-toed cowboy boots.
These tools will only tell you if the tire is totally flat.
Visually observing the deflection of the sidewall is not an accurate gauge of tire pressure either, since tire constructions that affect sidewall deflection vary considerably among tire manufacturers and from one tire model to another.
Summer's the time when freight shipments pick up, more trucks are plying the highways, RVers hit the road and vacationers head to the mountains or the shores. Everyone needs the proper air pressure to keep them safe and their trips as inexpensive and productive as possible.