As the costs associated with owning and operating trucks and equipment continues to rise, more and more truckers are seeking ways to control expenses.
“One simple and immediate way for them to save money is to properly maintain their tires, a key element of which is maintaining the proper inflation pressure for a given tire size and load,” says Harvey Brodsky, Managing Director of the Retread Information Bureau (TRIB). “This is critical for getting the most life out of tires and for better fuel economy.”
It is not the tire, but the air inside the tire that carries the weight of a vehicle, absorbs shock and keeps the tire in its proper shape so it can perform as designed, Brodsky points out. Over and above affecting rolling resistance and fuel economy, inflation pressures also influence handling, traction, braking and load carrying capability.
Tires flex when they roll, which bends the rubber and steel (used within the rubber to provide additional operating characteristics). This flexing generates heat - a tire’s worst enemy.
“A tire that is improperly inflated doesn’t roll as smoothly or as easily as it was designed to,” explains Brodsky. “Improperly inflated tires have an uneven, irregular tire footprint - that portion that contacts the road surface. This inconsistent shape leads to increased wear, reduced traction and performance, and handling and ride problems.”
And it doesn’t take long for this wear to occur, he says. At 55 miles per hour, a truck tire turns approximately 450 revolutions per minute.
When underinflated, a tire flexes more as it rolls, building up internal heat and increasing rolling resistance, which increases fuel consumption. There is a direct correlation between how much a tire is underinflated and how much faster it wears.
Wear is the result of friction created between the road’s surface and the tread as the tire rolls along.
When overinflated, excessive wear occurs at the center of the tread because it will bear the majority of the vehicle’s weight. Along with making for a harsher ride, overinflated tires tend to not absorb hazards like debris in the road and potholes as well, increasing the risk of sustaining a puncture or impact damage.
COSTS
Because improper inflation shortens tread life, tires will have to be changed more often, Brodsky says. Besides the expense of purchasing replacement tires, there is the additional costs for tire service and vehicle downtime. “Industry studies have shown that cost-per-mile almost doubles when tires - whether original or retreaded - are pulled early because of uneven or rapid tread wear,” he notes.
In comparison, air is cheap, and checking inflation pressures does not require a big investment in time. On average, it takes only about 20 minutes to check and adjust tire inflation pressure on an 18-wheel tractor-trailer. “An investment in time well worth making,” says Brodsky.
Brodsky advises checking tire pressure when a tire is cold - before a vehicle has been driven, or driven less than one mile. Once a vehicle has been driven, tires warm up and experience an increase in air pressure, resulting in an inaccurate reading. A hot tire can take up to four hours to cool down after a vehicle is parked.
Tire pressure ought to be checked regularly, at least once a week, and always with a properly calibrated tire gauge, he goes on. “Inflation pressure cannot be accurately estimated by kicking or thumping the tire,” stresses Brodsky. “Trying to determine if tires need air by thumping them is as effective as trying to determine if a vehicle’s engine needs oil by thumping on its hood.”
Value caps should be installed on all valve stems and be kept tight. Metal value caps are best, as they contain a rubber gasket to provide an air-tight seal. Most plastic caps do not.
Even well-maintained tires lose air pressure, Brodsky acknowledged, on average about one or two pounds per month. This is a natural occurrence as air permeates through rubber.
The use of various tire pressure monitoring and control systems can help. Some warn of low pressure. Others equalize air pressure for slow leaks. Still others help maintain air in a tire that is damaged, enabling the driver to get to a repair facility.
DUALS
It is important that tires in dual wheel assemblies be accurately matched. That means having the same tire size and air pressure and similar tread patterns and tread designs. The tires also need to be matched within a tolerance of not more than one-quarter of an inch in diameter and three-quarters of an inch in circumference.
Brodsky says inflation mismatches on mated dual tires can cause tire diameters to differ enough that the larger tire will drag the smaller tire. This results in rapid and irregular wear, especially on the “smaller” tire.
Tests by Bridgestone/Firestone found that a 5 psi difference created a 5/16-inch difference in tire circumference on a set of dual tires. In just one mile, this little difference caused the smaller tire to be dragged 13 feet. Figuring 100,000 miles per year, this tire would be dragged 246 miles. This same type of situation can occur if tread depth and design on dual tires are not properly matched.
Another element to promoting long tire life and getting more miles per gallon is total vehicle alignment, adds Brodsky. Misalignment can cause tire-to-road drag and scrub, plus undesirable lateral forces, resulting in irregular wear and diminished tire life, difficulty in driving and handling and reduced fuel economy. Depending on the misalignment conditions, a vehicle may not exhibit any poor driving characteristics.
That is why, like air pressure, alignment needs to be checked on a regular basis, he counsels. This includes trailer tire alignment.
The pre-trip walkaround safety inspection is an ideal time for a driver to look for wheel problems and tire injuries, continues Brodsky. By rubbing a bare hand along the tread and sidewalls, a driver can feel for flat spots, bulges, cuts, shoulder wear, sidewall damage, missing chunks of tread and other damage, all of which can result in tire failure.
“The best time to have a tire failure is before it happens,” he emphasizes. “Making a repair before a vehicle leaves on a trip is considerably less time consuming, aggravating and costly than having an on-the-road breakdown and service.”
APPLICATION
Tire selection also impacts a vehicle’s overall fuel performance. Because tread depth and design have the biggest single effect on rolling resistance, tires should be application-specific.
Retreaded truck tires also are available with application-specific tread designs. “Retreaded tires can - and do - perform as well as tires that have never been retreaded, and they do it at a tremendous savings over the high cost of new tires - as much as 50% less,” Brodsky points out. “Every major truck tire manufacturer, with no exception, designs its tires for multiple lives, meaning the tires are designed to be retreaded.”
There are other benefits to properly maintaining tires besides maximizing tire life and squeezing more miles per gallon. Tires that are well maintained have improved retreadability, says Brodsky. And retreading conserves natural resources because for every retread produced, one less new tire needs to be manufactured.
Retreading also helps the environment by reducing solid waste disposal problems. With retreading, tires stay on the road longer so fewer worn tires require disposal instead of many, which helps reduce scrap tire disposal problems.
For additional information, please contact the Tire Retread Information Bureau (TRIB) toll free from anywhere in North America at (888) 473-8732 or by e-mail at info@retread.org.
