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Commercial Tires

It’s in the Air: Proper Air Pressure is Key to Tire Performance and Optimized Tire Investment

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Truck fleets and commercial tire dealers probably already know that tire costs are second only to fuel when calculating total operating costs. Managing tires properly – and that means being diligent in keeping air pressures where they are supposed to be – can maximize tire dollars.

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In a Technology and Maintenance Council (TMC) tire failure study, 90% of failures were directly caused by underinflation, which had either existed for a substantial period of time or had been caused by road hazards.

For fleets, keeping tires properly inflated means dedicating a technician to the task of tire management or hiring a dealer representative (and encouraging drivers) to check tires on all vehicles – all axle positions – daily. Yes, daily! Okay, so we know that’s a tough maintenance procedure to enforce, but it’s one that is critical, and every effort should be made to follow through.

Why all the hype about air pressure? It’s simple. Over- or underinflated tires do not perform within their designed range. The footprint is altered, causing irregular wear; more internal heat is generated, which degrades the casing; and sidewall flex is altered, which could lead to sudden failure.

Maintaining the right air pressure helps optimize tire performance in terms of wear, traction, durability and overall life.

Then there is the relationship between air pressure and the load. Obviously, the vehicle’s load affects tire life. Here is what the Technical & Maintenance Council (TMC), Recommended Practice (RP) 235 says you need to know to determine the correct air pressure for a given load:

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• Tire size and load rating

• Weight carried on each axle

• Number of tires on each axle

• Maximum speed the vehicle travels during its operation

• Operational history

• Tire manufacturer’s data book or the Tire and Rim Association’s Yearbook, which provide load, speed and inflation tables for a given size and type of tire

The RP goes on to say that a constant 20% underinflation/overload decreases the life of a tire by 30%. If the underinflation/overload situation is 40%, the decrease in tire life goes to 50%. Overloading causes:

• Excessive deformation of sidewalls, increasing the chance of cutting

• Excessive temperature and stress, increasing fatigue of rubber and cords and weakening adhesion between rubber and cords

• Excessive movement of tread, accelerating wear and/or irregular wear

If all of these facts aren’t enough to convince you that proper air pressure is crucial to maximizing tire life, let’s talk about tire temperature. When a tire rolls, it generates heat. The lower the air pressure in the casing, the more the tire will flex, and the hotter it will run. As the temperature rises, the air in the tire is heated and it expands, which means the interior air pressure is increased.

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TMC states that tests have shown that air inside an 11R22.5 tire can reach 160ºF or greater, depending on air pressure, road temperature, ambient air temperature, altitude or other factors. If the ambient temperature was 70ºF when tire pressure was set, the pressure could rise 10% just from normal operation.

RP 235 recommends that you choose the appropriate cold air pressure for the loaded condition and maintain that pressure. Never bleed air pressure from a hot tire. And, remember, before checking or adjusting air pressure, let the truck sit for three to four hours.

Expert Advice

Al Cohn, commercial tire technical marketing manager for Goodyear, says, “Running underinflated tires wastes fuel and also leads to overheating and potential casing damage. This damage is often hidden and could lead to a dangerous ‘zipper’ rupture, where a tire can fail without warning due to casing damage.”

Make sure both tires in a dual assembly are kept at recommended inflation pressures so they are both carrying the load evenly, he says. Running with one dual tire underinflated not only puts stress on that tire, but also it overstresses the other tire and may ruin two good casings. On-road failures of a tire in a dual assembly must be dealt with as soon as possible, he suggests, as limping to a tire service facility miles away will impact both tires in the affected dual assembly. And, when replacing duals, always use tires with matching outside diameters.

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Cohn goes on to say, “It is important that fleets make their tire decisions based on real data from tires in their own fleets. They need to gather information over time on a sampling of tires, and fleets that run more than one brand of truck need to sample a certain number of tires from all vehicles and applications to get a realistic idea of wear trends.”

Another way to ensure that tire life is maximized is to assign well-trained individuals to their care. Typically, tire technicians are entry-level personnel who get assigned to handle tires, notes Goodyear’s Cohn, but more and more, fleets are recognizing the fact that if you get a well trained person to do the job, that individual can save the fleet a lot of money.

Goodyear offers extensive basic training, which Cohn refers to as Tires 101, to help fleets learn how to maximize their tire dollars by properly caring for tires and prolonging tire casing life. A fleet’s tire dealer can also be a tremendous source for training and on-site tire checks and service.

According to Guy Walenga, commercial tire engineering manager for Bridgestone/Firestone North American Tire (BFNAT), “Air pressure is still the first priority for maintaining tires and getting the most life out of a casing. Nearly 80% of fleet tires are in dual positions, a situation that requires there be no more than a 5% difference in air pressure between tires for optimum performance of the original tread and to protect the casing for retreading.”

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Walenga says that, ideally, drivers should be educated to do air pressure checks during pre-trip inspections of vehicles and use a proper, calibrated air pressure gauge instead of a hammer or pipe. He notes that if drivers find problems with tires, there should be a system in place to finish the loop – service should be immediate so delays do not occur.

Visual pre-trip tire inspections should include scrutiny of the casing, he says. Fleets should not allow tires to roll out with a nail in the casing or other damage that will decrease air pressure along the way or create the potential for failure.

Walenga says that fleets and dealers need to develop a comprehensive tire mounting procedure for new tires and retreads. Every tire in the fleet should be filled to the proper air pressure so that tires are concentrically mounted on wheels. The wheels need to be clean, and the tires need to have the proper lubrication at both the bead and seating areas.

Once the tires/wheels are mounted for service, they need to be visually inspected, which includes a check to make sure the guide ring is equal around the rim. If it is not, Walenga warns that the tire will show irregular wear within 40,000 miles of service.

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In addition, it is always good to have an alignment program in place that allows for quick alignment checks. A quick check is an easy way to determine if a total alignment is needed right then to avoid problems down the road.

Working Together

Some of the best tire maintenance programs rely on a good working relationship between a fleet and its tire dealer and/or retreader and can be key to getting the most from tires. To capitalize on the relationship, fleets may want to assign someone to work with the dealer and/or retreader and assess scrap tires to learn what patterns are occurring and how premature failures can be avoided.

When asked to name the most important factor in maintaining tires, Doug Jones, customer service engineering support manager for Michelin North America, says it’s maintaining proper air pressure. Jones agrees with Cohn and Walenga that training tire technicians is crucial, and he contends that an untrained person can destroy good equipment.

OSHA supports this view by requiring anyone who touches a tire to have basic training. There are several organizations that offer formal tire handling training. Tire companies provide training, and TIA offers an accredited commercial tire technician course.

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All About Pressure

According to Curtis Decker, national manager of field engineering for Continental Tire North America, “Everyone talks about air pressure. That’s because when the tire is properly inflated, it runs its coolest.”

Brand-new rubber is not cured when the tire is made; rather, it continues curing over the life of the tire until the compound reaches reversion at the end of its life, he claims. Additional heat will accelerate this process. When a tire is underinflated, the casing runs hotter and works harder, with more dynamic stress, shortening the life of the tire.

Once fleets put together a good air pressure program, the next step is to provide ongoing maintenance, which includes proper repair techniques and proper alignment. For repair practices, Decker suggests fleets adopt practices such as those outlined by the TMC tire RPs and guidelines offered by the Rubber Manufacturers Association (RMA) and TIA.

He goes on to say, “Fleets need to practice due diligence when specifying tires to make certain the correct tires are spec’d for the application. The new, fuel-efficient tires run cooler, which means they have potential to last longer. Retreaders are also making more fuel efficient tires that run cooler.”

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Monitoring Pressure

Tire life and driver safety depend on good tire maintenance. Tires are expensive, but they can provide a good return on investment if they are properly cared for. Fleets know that maintaining tire pressure is the secret to tire life. Many have successful programs in place. Some are using new inflation technology to make the job easier.

With all the problems faced by an improperly inflated tire, ArvinMeritor offers a solution that works while the vehicle is in motion. The Meritor Tire Inflation System by PSI uses compressed air from the trailer air brake system to inflate any tire that falls below a pre-set pressure while the trailer is moving.

The inflation system connects all tires on the trailer to a controlled air supply, which maintains air pressure at a constant, proper level – even while the vehicle is moving. As air pressure decreases from a recommended level, the system automatically supplies air to a control box and then into the axle. The air is then distributed to each tire, the company says, until the desired pressure is reached. The computer-controlled system compensates for pressure changes due to rolling temperatures.

Some system manufacturers say fleets have achieved a good return on the investment they’ve made for tire inflation systems. “Due to an identifiable return on investment of less than 12 months, there has been a rise in the popularity of ATI systems in the last few years,” notes Deryk Powell, COO at Velociti Inc., a mobile installation and deployment company that offers retrofit of automatic tire inflation (ATI) systems. “The faster you install your entire fleet with the systems, the sooner you will realize the benefits.”

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In the past, fleets mainly specified ATI systems on newly purchased trailers since they could be installed cost effectively at the factory. But with Velociti specializing in the remote retrofitting of ATI systems, Powell adds, the number of fleets installing these systems on existing trailers, as well as on tractors, is on the rise, a trend that is expected to continue.

Hendrickson International has come up with Tiremaax, an ATI option for users of its trailer suspension systems.

According to the company, Tiremaax is governed by an electronic control unit, which detects low tire pressure and signals the operator to situations requiring attention. It responds by directing air from the trailer tank to one or more tires when the inflation pressure dips below the pre-set level.

With the system, air travels from the supply tank through air lines inside the axle to the wheel ends. A ball-bearing rotary union allows air to flow through the axle spindle to the rotating hubcap fitting. Hoses then connect the hubcap tee to the tires.

Hendrickson says that Tiremaax activates only when needed – constant air pressurization to the tires is not required – reducing air demand and prolonging system and seal life.

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Underinflation Woes

The data supporting the need for maintaining proper tire inflation is significant, but there are some underappreciated aspects fleets should consider, as well. Maintaining proper tire inflation levels impacts the entire business – maintenance, fuel economy, logistics, customer service, accounting/purchasing, drivers and, most importantly, safety.

When tires roll in an underinflated state, the steel cords are over stressed and simply will not hold up. This makes retreading difficult, if not impossible. Wasted casings represent wasted dollars.

Proper tire inflation greatly reduces tire blowouts, which results in the rubber on the road you swerve to avoid while traveling down the highway. Not only are blowouts themselves dangerous, but hitting tire debris can cause tire and vehicle damage. And, a sudden blowout in traffic is dangerous to other motorists – and insurance rates.

Donald Lemke, fleet maintenance manager for USF Logistics, thinks about prolonging tire life daily. “Our goals are to improve fuel economy, enhance tire life and increase productivity,” he says. He has added super wides and the Airgo ATI system to improve performance and save on fuel.

“I anticipate savings to only improve as our fleet ages and fuel prices continue to rise,” Lemke says. “The small amount of time invested in the maintenance of the system and the warranty support received from our distributor has reinforced our decision to equip our new trailers with automatic tire inflation.”

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Another Option

From both productivity and cost perspectives, fleets often have to live with the pitfalls of improper tire inflation. It’s a constant cost/benefit balancing act.

However, there are alternatives, such as nitrogen.

Nitrogen is used as a substitute for air in aircraft tires, race tires and a handful of commercial applications. And in the past year, nitrogen has become a very popular alternative for fuel-cost-conscious consumers.

Inflating tires with nitrogen in place of compressed air is not a new idea. In fact, it was first developed for use by the trucking industry. But, despite recent consumer-level interest, it’s still not very common in the trucking industry.

Nitrogen suppliers point out that air, comprised of mostly oxygen and nitrogen, migrates through the walls of tires three times faster than nitrogen alone. That means that tires stay properly inflated longer. Plus, as air migrates through the tire carcass, the oxygen has an opportunity to oxidize the tire’s steel cords, which can damage the casing and shorten its useful life.

Because nitrogen is dry and stable, it will help prevent wheel corrosion and rust. The inert gas is non-combustible and does not hold heat as air does, so tires can run cooler.

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Air at a Glance

Looking for an easy way to check air pressures? There are a couple of innovations on the market today that can make checking air pressure a whole lot faster and easier.

Earlier this year, Stemco introduced its BAT RF products, which includes the AirBAT RF, a monitor that provides instant visual reading of tire air pressures and the ability to transfer the data by radio frequency. The unit can be quickly and easily installed, the company says, in less than 10 minutes on any dual tire wheel end.

The data is collected by the hand-held tool and is transferred to a PC in the fleet’s maintenance department. According to Stemco, the heart of the system is the sensor that continuously monitors and tracks mileage and tire pressure. Wireless RF data collection enables fleets to gather accurate tire pressure information (and mileage) quickly and efficiently, the company says.

Michelin North America recently introduced a computerized chip that mounts inside tires, which monitors and records detailed pressure and temperature information. The eTire system includes a hand-held scanner that allows technicians to read data on both inside and outside duals at a glance.

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The eTire System incorporates the company’s InTire Sensor, sidewall-mounted SensorDock, a hand-held and drive-by reader and its BIB Track software to capture and instantly report tire pressure, wheel position and maintenance information. The InTire Sensor can be installed in any brand of truck tire, the company notes, which means a fleet can monitor and track every tire in its operation.

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