This year, the U.S. interstate highway system marks its 50th anniversary. It is not surprising to drivers who travel these roads that, amid the ever-rising cost of a barrel of oil, and the proliferation of eco-friendly hybrids and alternative fuels, trucks still rule the highways and their many adjoining capillaries.

While the percentage of trucks on the highway at any one time is small – they account for about 4% of the vehicles burning rubber on more than 1.5 million miles of concrete and asphalt across the country – trucks play a major role in keeping the nation moving.

The American Trucking Associations (ATA) recently reported that trucks transported 68.9% of the country’s total freight volume last year, or 10.7 billion tons of goods, and generate $623 billion in revenue, or 84.3% of the country’s overall freight bill.

Further, the ATA said that more than 26 million trucks of all classes played a part in reaching the milestone. Of this number, 2.7 million were typical Class 8 tractor-trailer combinations operated by 565,000 interstate carriers.

They also consume a great deal of fuel.

According to the U.S. Department of Transportation and the Federal Highway Administration, it is estimated that trucks traveling in the U.S. consume more than 27 billion gallons of fuel a year. That compares to more than 13 billion gallons of fuel used by airplanes annually.

Fleet owners and operators are well aware of the numbers, and they are also aware of the costs involved in shipping goods across the country.

The ATA last conducted a cost survey with 20 major carriers in 2004, and the results indicated that, while the number of miles driven in one year declined from the previous year, annual operating expenses for one rig averaged $154,344. That was an increase of 6.3%. During the same period, net profit margins decreased from 7.71% to 6.41%. Managers whose responsibility it is to maintain trucks and fleets have been challenged to cut those operating costs.

There are very few ‘new tricks’ left to reduce expenses, so many of the service bay watchers are revisiting some of the old standards. Reducing fuel costs is now an automatic task today. It always seems to be at or near the top of everyone’s list.

One major area often taken for granted in the battle to improve fuel economy and efficiency is where the rubber meets the road. Tires play a significant role in that endeavor, and tire maintenance is one area where the return on fuel investment can be increased with a minimum amount of capital and a concentrated effort.

“Generally speaking, fuel economy is something we’ve been thinking about for the past 15 years,” says Greg James, engineering manager for commercial products for Bridgestone/Firestone North American Tire (BFNAT). “In the 1980s, we didn’t think about (fuel efficiency in tires) that much, but in the 1990s, it came up on everyone’s radar, especially with the EPA’s requirement for reduced emissions.”

Of course, BFNAT and other major tiremakers will tell you that you can decrease fuel costs if you buy their specially developed tires. All major tire companies offer fuel-efficient tires with low rolling resistance. While such tires can improve vehicle fuel efficiency all by themselves, according to all the tire companies, gains in fuel-cost reduction can be enhanced more effectively by reducing the many other environmental factors that affect fuel usage.

Just like buying real estate, those options start with a universally accepted recurring plea – inflation, inflation, inflation – but this doesn’t refer to national economics.

“Keep the darn things (tires) inflated,” says James. “Every driver should have a tire gauge and use it every day.” Despite decades of reminders from tiremakers and trade publications alike, “most don’t understand the impact that tire maintenance has on fuel economy,” admits James, “and it starts with the correct pressure in each tire all the time.”

Scott Rhodes, director of commercial products for Cooper Tire & Rubber Co., agrees with his counterpart and says that the importance of checking inflation cannot be overstated.

“In spite of the fact that fuel costs are rising, and were already the No. 1 non-personnel cost for fleets, there has been relatively little demand from users for fuel-efficient tire products as a means to mitigate the impact of increasing fuel costs,” Rhodes says. “For many fleets, simply maintaining tire inflation pressures at target levels would significantly reduce any effect of tires on fuel consumption.”

Rhodes says it is important also to select the right tire, but adds: “Fuel efficiency can certainly be a criterion to use in tire and retread selection, but a number of other, more significant factors can easily mask the tire and retread effect on overall vehicle or fleet fuel efficiency. This makes it difficult for fleets to measure any benefit gained from more fuel-efficient tires and retreads.

“Fleets that are most likely to recognize a benefit are those with excellent maintenance of tires and tire inflation, wheels, suspensions, alignments and with consistent routes and driver habits,” says Rhodes. “New tires and retreads are only a part of fuel efficiency related to a tractor/trailer. Vehicle aerodynamics, engine size, driver habits, and other issues all combine to impact fuel efficiency. Combining the most fuel-efficient tires with a vehicle that is too heavy, with too much horsepower and a driver that pushes the truck hard will probably not gain the efficiency designed into the tires.”

Eliminating Resistance

So, how can tires have such a significant impact on fuel economy, and what consumes fuel?

In one word, speed. It is the biggest factor, but there are two major contributors to speed that affect fuel consumption for a truck moving down the road – air resistance and tire rolling resistance.

Air resistance plays a large role in the amount of fuel consumed. That’s why truck manufacturers work so hard to improve the aerodynamics of their equipment.

While most owners and operators don’t design their own trucks, they can help themselves in the battle to increase fuel efficiency by focusing on what they can control – tire rolling resistance.

Tire rolling resistance is the amount of drag created by the tires as the vehicle runs down the highway. Anyone who has rolled a truck tire across a service bay knows that it takes some effort, but try to do it at 55 miles an hour with several thousand pounds of load on it, and it’s a different story.

Research from BFNAT reinforces the premise of speed significantly impacting fuel efficiency. In one test, vehicles went from about 4.5 miles per gallon at 65 mph to about 6.5 miles per gallon at 30 mph. But, they admit that, while 6.5 mph is an improvement in fuel efficiency of 44%, cutting speed to 30 mph is not a very realistic way to save fuel or to get product to its destination on time.

Like air resistance, rolling resistance is an important factor that increases with speed. In fact, part of tire rolling resistance is the aerodynamic resistance of the tire itself as it moves.

Because tire rolling resistance is not the only factor involved, an improvement in rolling resistance doesn’t produce an equal improvement in fuel consumption.

No Silver Bullets

One end user that understands the importance of regular tire maintenance is Knight Transportation, a BFNAT fleet customer based in Phoenix. Dave Williams is vice president of engineering and maintenance for Knight Transportation, and oversees its fleet of more than 3,200 vehicles and 3,500 employees.

“A lot of it is just common sense,” says Williams, a 15-year Knight veteran. “There’s no silver bullet for this.”

Knight Transportation certainly has some credentials. It has made Forbes’ prestigious list of “The 200 Best Small Companies” for 11 straight years and ranked as high as 60th in 2003. It was incorporated in 1989 and, three years later, reported sales of $13 million. The now publicly traded company announced a 3-for-2 stock split this past December, and posted 2005 sales of $499 million – a 21% increase from the previous year.

Knight Transportation lives by a key tenet in all of its operations, one that is directly applicable to its dedication to regular maintenance. “In order for it (maintenance plan) to be effective, you have to be disciplined,” says Williams. “There are several key components to a plan, but discipline should guide it.”

A few of the key tire recommendations that Williams lists include:

• Inflation. Continuously check the pressure in all the tires.

• Pay attention to rubber compounds and tread design, and make decisions for tires based on intended use of each vehicle. How heavy are your loads? What kind of roads are you driving on? What kind of scrubs are you getting?

• Check wheel alignment regularly.

As a general rule of thumb, Williams says that Knight conducts a thorough maintenance check on its trucks at every 30,000 miles and every four months on trailers. “But, you have to determine what’s best for your own applications,” he says.

While some fleets have moved away from regular alignment checks, Goodyear’s Tim Miller, marketing communications manager for commercial tires, agrees with William’s recommendations.

“If any of the wheels on an 18-wheel tractor-trailer rig are not properly aligned, the total drag on the vehicle increases,” says Miller. “This causes a greater ‘scrub’ of the tires against the road surface and, potentially, greater aerodynamic drag when the tractor and trailer are not tracking parallel to the direction of travel.”

Another factor that affects overall fuel efficiency, including tire performance, is an individual’s driving style.

“Aggressive drivers can negate many of the gains obtained from a fleet’s investment in fuel-efficient tires, engines, aerodynamic devices or synthetic lubricants,” says Miller. “With today’s technology, it is possible to accurately measure the amount of fuel an engine uses over a period of time, so programs can be set up to reward drivers for fuel efficiency.”

Miller also says that other factors, such as ambient air temperature, weather conditions, road surfaces (gravel, asphalt, concrete) and terrain (flat, hilly or mountainous) are environmental factors that are impossible to control but have a direct effect on fuel consumption.

When it comes down to specific tire fuel efficiency issues, though, Miller said that owners and operators should focus on a couple of positions.

“While each of the wheel positions contributes a portion to the total tire rolling resistance, the drive and trailer tires account for more than 85% of a truck’s tire-drag forces,” Miller says. “We concentrate fuel efficiency efforts on these axle positions.”

Setting Standards

Even with such a focus, the bottom line in maximizing investment in truck tires still comes down to having an effective maintenance program – including a standardized policy.

Michelin North America’s Doug Jones, customer engineering support manager, said that, to get the most out of truck tires, “fleets that don’t already have a written tire maintenance policy, which is properly communicated and monitored, need to develop one. The policy needs to state established air pressure data, loads carried by vehicles and how often tires are to be inspected.”

Jones also recommends including specifics, such as when to remove tires for retreading. “This also needs to be spelled out in any policy, as well as guidelines for the number of retreads expected for tires,” he says. “The policy needs to cover each tire and how it will be managed from the new tire’s first position as a steer tire, through the move to the drive position where the tire might be retreaded once or twice, then to the trailer position – with the number of retreads expected for this last position.

“A good tire policy needs to include age specifications, which describe the expected life of the tire casing within the fleet. Fleets need to make this determination based on its application and on data related to how tires perform in that application,” he says. “And, you need to make determinations related to acceptable condition of a casing for retreading, such as the number of nail holes and repairs accepted. Fleets also need to check tires for cracking or deterioration from exposure to ozone, which may eliminate the casing as a good candidate for retreading.

“After collecting tire data, fleets may find that there are certain changes that can be made for greater efficiency or better cost savings. The main thing is to have a written policy related to their tire business and retreading. And, they should establish and maintain a good working relationship with their dealer and retreader. Those relationships include giving them a copy of the tire policy.”

In tune with the rest of the industry, Jones says, “Without a doubt, the most important factor in maximizing tire fuel efficiency and tire life is maintaining proper air pressure.” Right behind that are maintaining proper alignment and establishing rules of thumb for removal mileage.

“You need to be careful not to run the tread down to a point where the tire can’t be retreaded, which would be 4/32nds on the steer position and 2/32nds on the drive position,” he says. “Better pull points are 6/32nds for steer and 8/32nds for drive.”

Jones is also adamant that tire technician training is crucial. “An untrained person can destroy good equipment. In fact, OSHA supports this view by requiring anyone who touches a tire to have basic training,” Jones says.

There are several options for formal tire handling training, including the Tire Industry Association and tire companies.

Michelin’s Jones thinks training should be taken a step further. “Training should also be provided to drivers. Tire air pressure should always be checked during the pre-trip inspection, and the drivers should take a good look at the condition of the tires in all positions. If repairs are needed, they should be handled immediately to avoid problems. If the tread is low, the tire should be pulled.”

Establishing a Program

From a good tire maintenance standpoint, Jones says, “There are two approaches you can take. Some fleets prefer to do it all in house, while other fleets choose to outsource all or part of their program. Either way, it is a good idea to work with a dealer that is close so it can assist the fleet in emergency situations and is willing to work with the fleet in reducing overall tire and fuel costs.”

Bottom line: It all comes down to setting procedures and following them to a T. Here is handy list of key things any fleet – and tire dealer – can do to improve a fleet’s tire fuel efficiency:

1) Have the right tools to check air pressures. Every shop should have a master air gauge, and all shop gauges should be properly calibrated off that master gauge. Every driver should have an accurate pressure gauge and be instructed to check the tires on their truck every day. No tire thumping!

2) Drivers should conduct a visual inspection of their vehicle’s tires prior to operating the vehicle. They should look for signs of irregular wear in the tread or shoulder areas of their tires and examine the tires for bubbles or bumps, which may be caused by air infiltration or foreign objects.

3) Make sure inflation pressures are correct for the loads being carried or the conditions the vehicle will face.

4) Check tires for correct air pressures. A tire that is 20% below the optimal air pressure is considered a flat tire. A tire that is run under these conditions will experience casing fatigue that could lead to a catastrophic failure or a zipper rupture. If the tire has been run 20% underinflated, it should be removed from the vehicle and scrapped.

5) Beware mixing tires on your vehicle, especially across an axle. Match tires with the same tread depths, same tread patterns and same height (overall diameter).

6) Use the right tire for the job. Drive axle designs do not belong on trailers. Steer axle tires are not intended for drive axle positions. Using the right tire – in the right position – for the job will automatically improve fuel efficiency.

7) Work with your dealer and/or retreader to ensure that fuel efficiency is top of mind when spec’ing retreads. As with new tires, the wrong tread pattern or compound will hinder fuel economy.

8) Just because it’s a retread doesn’t mean you stop taking proper care of it. Thousands of miles – and real dollars – can be lost by disregarding proper tire maintenance practices once a tire is retreaded.

9) Look at all alternatives. Do you need to run new tires on every axle position? Are you a candidate for using super wide drive and trailer tires? Are you buying on short-term price and not long-term return on investment?

10) Create a culture oriented toward fuel economy, and involve everyone from the shop bays to the drivers to management to suppliers. Get everyone’s buy in and be diligent in establishing and meeting goals.