A simple and immediate way to make the most of the money spent on fuel and tire purchases is to pay greater attention to proper tire maintenance, the heart of which is air pressure. By maintaining the proper inflation pressure for a given size of tire and load, tires will provide the best fuel efficiency and safety, while minimizing wear for longer tread life and maximum retreadability.
The challenge has always been how to maintain the proper inflation pressure. The task can be made more manageable through the use of such technology as nitrogen inflation and tire pressure monitoring system.
It is the air inside the tire that carries the weight of a vehicle, not the tire, explain tire professionals. The air supports the weight, absorbs shock and keeps the tire in its proper shape so it may perform as designed. Tires, which serve as the container for the air, are designed to be run at a specific pressure based on how the tire is constructed and the amount of weight that it is carrying.
In addition to affecting rolling resistance, and thus fuel economy, inflation pressure also influences handling, traction, braking and load-carrying capability.
Improperly inflated tires have an uneven, irregular and inconsistent tire footprint (that portion that contacts the road surface), tire professionals point out. Because the tire doesn't roll as smoothly or as easily as it was intended to, fuel efficiency declines, as the engine has to work harder to keep the truck moving.
Tires are made of layers of fabric and steel cords encased in rubber. Tires flex when they roll, which bends these components.
Tire manufacturers agree that underinflation - when a tire has lower than specified air pressure - is a major contributor to premature tire failure and poor tread life problems. The reason being: underinflated tires generate a surplus of heat through friction and additional flexing of the steel belts which generates heat, and heat is a tire's worst enemy.
Excessive heat build-up in the tire creates dangerous driving conditions, they note, and also shortens tire life by rapidly increasing tread wear. There is a direct correlation between how much a tire is underinflated and how much faster it wears.
Underinflated tires also cause more frequent blowouts and punctures, requiring costly road service.
Because underinflated tires tend to run hotter, retreadability is diminished.
Truck and bus tire manufacturers design their tires to be retreaded, so it's important to protect the casing for reuse through retreading.
Another cause for concern is tire pressure in mated dual tire and wheel assemblies. Inflation mismatches on these 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.
Tire pressure should always be checked when a tire is "cold," which tire professionals say, is 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 and that causes an inaccurate reading.
They also recommend that tire pressure be checked regularly, at least once a week, and always with a properly calibrated tire gauge. Inflation pressure cannot be accurately estimated by kicking or thumping the tire. As one tire professional put it: "Trying to determine if tires need air by thumping them is as effective as trying to determine if the vehicle's engine needs oil by thumping on the hood."
In spite of the fact that regularly checking tire pressure is one of the most important maintenance procedures, it is one of the most difficult to enforce. And even with the best preventive maintenance programs, maintenance personnel too often overlook checking some tires or even entire vehicles. Moreover, even the best of maintenance programs can't prevent tire damage resulting from a loss of air pressure while on the road.
Technology, through the use tire pressure monitoring and control systems, is helping to do away with these concerns. Some systems 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.
A tire pressure monitoring system (TPMS), basically, is an electronic system designed to continuously check the air pressure inside a tire. These systems report real-time tire pressure information to the driver of the vehicle in a variety of ways.
With recent advances in microchip technology, electronic tire pressure monitoring is now an affordable tool for both large and small fleet operations alike, and is an indispensable necessity for trucks or trailers with wide-based (super single) tires, says Richard Van Dyke, vice president, Fleet Specialties Co., Tire Sentry Div. "Both on-board and hand-held electronic tire pressure monitoring can be a particularly useful tool to support or enhance most any preventive maintenance program,"
There are tire pressure monitoring systems that can monitor tires when the vehicle is on the road, and also when stationary, which makes it possible to check tires for low pressure before leaving the yard and at the end of the day. An example is Tire Sentry Div.'s Yard Man - a hand-held receiver/display that enables low tire pressure to be automatically checked while the user walks by a truck equipped with electronic tire sensors (electronic valve caps).
Van Dyke says tire pressure monitoring systems provide a number of benefits. Among them:
• Frees maintenance and yard personnel for other tasks.
• Helps extend useful tire life.
• Helps reduce road service calls for tire problems.
• Helps increase fuel efficiency.
• Increases the efficiency of PM programs.
• Helps reduce overall tire and maintenance cost.
Fleet Specialties' Tire Sentry Div. was the first to introduce tire pressure monitoring systems designed specifically for the trucking and transportation markets.
Automating the tire pressure checking function reduces the need for manual pressure checks and increases the frequency and accuracy of pressure checks. That's because onboard tire pressure monitoring systems - such as the Doran 360, SmartWave, Pressure Pro, TireVigil, SmartTire and Tire Sentry - provide real-time alerts to low-pressure situations to the driver. This adds greater safety for the driver and vehicle by enabling drivers to get problems fixed as they occur, which helps avoid costly blowouts, tire-related road service calls and downtime.
Depending on the system, alerts are provided in a number of ways and for various conditions. Some systems tell the exact air pressure of each tire on an in-cab display, while some systems have a red light/green light display. Others provide an indication on the axle end when a tire problem is detected. Among TPMS features and capabilities: alerts when tire pressure is too low, alerts when tire pressure is too high, alerts with both visual and auditory warnings and monitoring both the vehicle and trailer.
"A typical truck TPMS can provide the driver with the current tire pressure in the cab either while sitting still or moving," notes Chris Nau, national sales manager, Doran Manufacturing. "Along with tire pressure readings, today's truck TPMS offer additional features such as audible and visual alerts when the tire pressure drops to unsafe levels, notification for high pressure or temperature, alert history or data logger and the ability to monitor trailer tires even in a drop-and-hook fleet."
Some systems, like TireVigil Pro, incorporate telematics to deliver tire-related information off the vehicle to dispatchers, maintenance personnel and fleet management. This gives them greater visibility of their fleet's tires, whether their vehicles are hundreds of miles away, rolling down the road or parked.
Earlier this year, Doran Manufacturing joined with DriverTech - a builder of onboard computer system for vehicles - to develop a product that forwards a low tire pressure alert received by the Doran 360 TPMS to dispatch and/or maintenance personnel. In September, PressurePro and Haas GPS announced their integrated TPMS/tracking solution - the new H1440. The unit combines traditional business tracking information such as location, engine on/off and speed violations, with automatic and on-demand real-time tire pressure alerts.
This off-the-truck communication enables dispatch, fleet or maintenance personnel "to react and assist the driver in developing a game plan on how to best address the tire issue before catastrophic tire failure and costly downtime occur," Nau says.
There are two ways to monitor whether a tire has lost pressure: indirect and direct. Indirect monitoring systems uses the vehicle's antilock brake computer to measure the circumference of each tire and then compare the dimensions to find a tire that may be low or have lesser circumference. On a tire that is low on pressure, its circumference changes enough to roll at a slightly different number of revolutions per mile than the other tires.
The direct tire pressure monitoring method uses a wireless pressure sensor, attached either inside or on the outside of the tire, to send the pressure data to a receiver in the vehicle. These systems measure, identify and warn the driver of low pressure. With a sensor in each wheel, they generate accurate warnings and can send a real-time alert if the pressure in any one tire falls below a predetermined level due.
"The direct method has somewhat become the standard over recent years because many trucks have dual tires and limit the effectiveness of measuring the tire circumference," observes Nau.
There are also automatic tire inflation systems (ATIS) that monitor and continually adjust the level of pressurized air to tires. Unlike a tire pressure equalization system that keeps inflation pressure and load distribution equal by distributing air from one tire to another, ATIS maintains proper tire pressure automatically, with no action required by the driver.
One type of system uses the vehicle's existing air-brake compressor to supply all of the tires from a central source. Another type of ATIS uses self-contained compressors mounted on each hub that are powered by the rolling motion of the wheels. Both systems keep tires properly inflated even while moving.
The concept of automatic inflation works best on trailers because the hollow trailer axle and hub allows for an exit point for the air supply to get to the tire valve stem, says Doran Manufacturing's Nau. This technology is not conducive to a truck application because of the solid steer spindles and drive axles.
Also, an active inflation system requires moving parts which have tendency to require additional maintenance and because the tire is automatically inflated serious tire issues can easily be over looked.
The first company to develop automatic tire inflation system technology for commercial trailer was PSI. The Meritor Tire Inflation System (MTIS) by PSI uses compressed air from the trailer's air system to inflate any tire that falls below a preset pressure whenever the vehicle is in operation. As air pressure drops below the tire manufacturer's recommended level, MTIS automatically routes air through a control box, then into each axle. The axles carry the air to a rotary union at the spindle that distributes the correct amount of air to each tire as needed.
Other automatic tire inflation systems for trailers are offered by Airgo Systems, Dana Spicer, Hendrickson and Pressure Guard.
"With all of the increased efficiencies possible with automatic tire pressure monitoring, and considering the more miles driven, the faster the return on the investment," says Van Dyke of Fleet Specialties' Tire Sentry Div. "An average of six to 10 months may be quite realistic for a tire pressure monitoring system to pay for itself.
"Often, just by saving one tire and a road service call you can will pay for the system on that vehicle."
Along with improved safety, truck owners and operators will also get a return on investment "realized through better tire wear, longer tire life, less number of on-highway catastrophic tire failures, a lower loss of retreadable tire casings and finally an increase in fuel economy," adds Nau.
The Transportation Recall Enforcement Enhancement, Accountability and Documentation (TREAD) Act was passed in the fall of 2000 as a result of the Ford/Firestone crisis. That situation involved a high incidence of tire failures on Ford Explorer vehicles equipped with Firestone tires. The law came about because Congress wanted to make tires safer for the motoring public.
Among the major components of the TREAD Act that affect the tire industry are: tire labeling requirements, tire testing standards, an early tire defect warning reporting system, an established recall processes, recalled tire tracking, disposal of recalled tires and tire pressure monitoring systems as standard equipment from the OEMs.
"The TPMS requirement was the detail that helped advance the TPMS technology to a viable and reliable option in the automotive industry," Nau says. "These advancements have trickled down into the heavy duty trucking industry."
Since Congress has already mandated the installation of TPMS on new vehicles under 10,000 pounds gvwr, Van Dyke figures it may be only a matter of time before Congress expands the TREAD Act to also include trucks, buses and other pubic conveyances, including emergency vehicles.
Along with TPMS, another technology that can be used to help maintain proper tire inflation is filling tires with nitrogen instead of compressed air. Nitrogen inflation proponents says nitrogen allows a tire to retain more of its original properties so there is less inflation pressure loss for a more stable and consistent tire pressure, longer tread life and less oxidation of tire components. This assists in increasing tire life, improving fuel economy and reducing tire aging.
Because of its inherent benefits, nitrogen been used for many years used to inflate aircraft tires, off-road truck tires, military vehicle tires and race car tires. Among the key benefits: Tires inflated with nitrogen don't lose pressure as quickly as those filled with air, and since nitrogen disperses heat quicker than air, tires run cooler.
Nitrogen tire inflation in on-highway transportation has been evolving with the greater availability of nitrogen, as on-site nitrogen generators have become more affordable and as more manufacturers of nitrogen generators have entered the marketplace.
Nitrogen is a non-combustible, inert gas that makes up about 78 percent of the air we breathe. The remainder of the atmosphere is oxygen, except for about one percent which is made up of gasses and water vapor.
Air contains oxygen, and oxygen is affected by changes in temperature, especially at high pressures and temperatures. When oxygen reacts with things, the process is called oxidation.
Water vapor and humidity inside of tires is also a concern, as they can cause extreme pressure fluctuations as a tire heats up going down the road.
Being a dry, inert gas - not readily changed by chemical reaction, nitrogen doesn't fluctuate, but rather, provides constant pressure and is less susceptible to accelerated diffusion caused by changing temperatures. Plus, it helps reduce water vapor and humidity in tires.
Because nitrogen inflation minimizes moisture and oxygen in a tire, there is less rubber degradation and no corrosive properties as found in compressed air, say nitrogen suppliers. A reduction in rubber oxidation slows a tire's "aging," improving the casing's structural durability, lengthening its useful life and yielding a higher proportion of retreadable casings that can survive more retread cycles.
Furthermore, because nitrogen's molecules are larger and less permeable than oxygen and all the other gases in air, they migrate considerably slower through a tire. It might take a truck or bus tire inflated with nitrogen about three months to lose two psi, whereas even a well-maintained tire inflated with compressed air will lose, on average, about two psi per month - a natural occurrence as air permeates through rubber.
Nitrogen is also far less reactive, nitrogen suppliers note. It doesn't cause rust or corrosion on steel or aluminum, and it doesn't degrade rubber. Wheel surfaces stay smooth and clean, and rubber remains supple and resilient.
Depending on the type of fleet or service provider application, converting to nitrogen could take place in a variety of ways, says Ken Lawton, president of GoNitro Tire. While nitrogen tire inflation systems have traditionally been fixed systems in a shop or service center, recent innovations provide significantly increased flexibility with new mobile systems. Additionally, once the initial conversion is complete, top-offs and ongoing maintenance can be handled using either fixed or the new portable systems.
For small to medium size fleet and service operations with a central depot, fixed nitrogen tire inflation systems are a good option, he says. These operations should verify the capacity of their existing compressed air system while taking into consideration any additional requirements of the nitrogen inflation system.
Generally, systems will require 12 scfm (standard cubic feet per minute of air) at 110 to 160 psig (pound-force per square inch) for each 4 cfm (cubic feet per minute) of nitrogen, says Harold Wagner, national sales manager, Kaeser Compressors. The amount of air will only be required while the nitrogen generator is in operation. Depending on the number of vehicles, multiple nitrogen generators may be required.
The air should be clean and dry, he goes on. The existing clean air treatment equipment ought to be checked to ensure it provides a maximum dew point of 50°F and that the system includes a coalescing oil removal filter to eliminate trace contaminants.
Further, Wagner recommends identifying and repairing air leaks. Studies indicate that as much as 35 percent of all compressed air produced is lost to leaks. In addition to increasing energy costs, this can also reduce the effective capacity of the system.
Larger, heavy duty fleets can be more of a challenge, observes Lawton. Not only are tractors and trailers often stored in different locations, but the conversion phase will require more resources than the maintenance phase. In these situations, mobile tire inflation systems that combine a small portable, gas driven compressor and a high purity nitrogen tire inflation system are ideal. These units are completely contained and include all necessary equipment and accessories.
Taking advantage of technology to keep tires properly inflated helps increase vehicle safety, improves fuel economy, enhances vehicles performance and increases tire and tread life, say tire professionals. But there are additional benefits as well.
By being more fuel efficient, less fuel is consumed. This saves money at the pump, decreases petroleum fuels demand and reduces emissions and pollution.
Along with lasting longer, tires that are well maintained have improved retreadability, which conserves natural resources and helps the environment by reducing solid waste disposal problems.