IN TODAY'S economy, carriers are looking at all ways to enhance their bottom lines. Tires rank almost as high as fuel where costs are concerned, which means careful consideration is required for their purchase and maintenance in order to bring operation costs in line.
There are many tire offerings in the marketplace. In addition to traditional truck and trailer tires, wide-base singles are taking another run at the US truck market. Also gaining popularity among fleet managers are automatic pressure control and monitoring systems.
On the super-single side of the market is the Bridgestone Greatec line. Goodyear started production two years ago on its first wide-base tire that fleets are now testing. Continental General Tire Co has a product that is in a testing phase with several fleet partners. Michelin is marketing the X-One XDA series in a drive pattern and XTA series in a trailer pattern.
The tires are expected to offer better fuel economy and increased payload. Other benefits include rig stability, lower wheel costs, and extended brake drum and lining life.
On the downside, fleets are concerned that the new tires are not widely available. Other potential negatives of wide-based tires include tire weight, which makes it awkward to handle and puts greater stress on the bearings.
Latest additions in the traditional truck tire lines include Continental General Tire's HSR, a steer tire for regional service. It has a special tread design with a depth of 23/32nds and a pyramidal stone ejector to reduce stone retention. A 16-ply casing delivers maximum in retreadability, according to the company.
Whatever tire models are chosen, controlling pressure is critical to the performance. One way to control tire pressure is to install automatic regulation systems. Dual Dynamics, Lincoln, Nebraska, offers Crossfire, a dual-tire pressure equalization system. The product also has a feature that automatically isolates the good tire in the event of a blowout. When a blowout occurs, the internal safety valve closes immediately with only a slight loss of pressure to the good tire. In slow leak situations, the valve isolates other tires after a pressure drop of approximately 10 psi.
The Meritor tire inflation system by Pressure Systems International (PSI), San Antonio, Texas, automatically monitors and maintains inflation levels. The system disperses as much air as needed to keep a tire inflated until service can be performed. Meritor estimates that more than 80% of fleet tire problems are caused by improper inflation.
Dana Spicer, Cleveland, also offers a tire pressure control system. It is designed to allow tire pressure adjustment from the cab. The system produces a better ride, lower step-up height, and reduced driveline maintenance, according to Dana Spicer.
Taking air from the same compressor that supplies the brakes and other on-board systems, the tire pressure control system uses a series of electro-pneumatic controls, feeding air to the wheel ends as required to regulate tire pressures. Steer, drive, and trailer axle pressures can be controlled using the system. Most tandem drive axles (40,000 to 52,000 pounds) and single drive axles (21,000 to 26,000 pounds) can be configured to work with the system.
Bridgestone Corporation of Japan has developed a system, Aircept, for its line of widebase single radials. The Aircept (assistant inner ring interceptor)unit fits around the rim inside the radial. Any sudden loss of pressure causes the unit to expand and support the load. Initially, the system will be available only in Europe, but as markets develop and the company's super single tires become popular in other parts of the world, the system's offering may be expanded, according to the company.
The system begins to expand if tire pressure drops below a specified level. By the time a total loss of pressure occurs, the unit has expanded to fill the interior of the tire, supporting the load. The system operates in conjunction with a tire pressure monitor that alerts the driver to the loss of air pressure.
Michelin Americas Truck Tires has introduced its eTire system that incorporates an InTire Sensor, sidewall-mounted SensorDock, hand-held or drive-by reader, and BIB TRACK software to capture and report tire pressure, wheel position, and maintenance information. The information gathered is reported in a fleet specific manner via an Internet server to enable maintenance managers to track tire costs and monitor inventories.
Texas Instruments (TI) Sensors and Controls developed the core technology for Michelin's InTire Sensor, a sensor that combines truck tire identification, and real-time pressure and temperature monitoring into one device. The InTire Sensor was introduced as part of the Michelin eTire System, an asset management system.
The InTire Sensor is a device that provides tire identification and tracking as well as real-time monitoring of tire pressure and temperature. The sensors are mounted inside a tire on the inner liner, using the Michelin SensorDock. The InTire Sensor uses a capacitive MEMS (micro electro mechanical systems) device to sense pressure and temperature.
Hand-held or drive-by readers installed at fleet depots or truck stops are used to wirelessly communicate with the sensor to read the digital pressure, temperature, and identification information that can be uploaded to Michelin's BIB TRACK software through the Internet. InTire Sensors are also mounted on the truck and trailer to automatically identify and link each tire to a specific truck.
All the monitoring in the world isn't enough, if the tires aren't selected that fit the job. Tires are designed for specific applications and uses. Each has advantages and disadvantages depending on vehicle design and the expected duty cycle. To keep overall tire costs down, tires should be matched as closely as possible to the application, according to information from Goodyear Tire Co, Akron, Ohio.
Radial tires dominate the trucking market today, and are used in mixed service applications, and typically have one steel body ply or multiple plies of other materials. The tread area of a radial is rigid, which gives longer tread life, more resistance to tread area punctures, and better fuel-efficiency. A key advantage of radials is that they run cooler.
“Heat is the tire's enemy,” says Al Cohn, manager, training and technology for Goodyear Tire Co. “The more you can do to keep a tire running cooler, the longer the life of the tire.”
Tires play a crucial role in supporting the vehicle's load, so it's important to consider maximum axle loading in the tire specification process. All tires have specific load limits at defined speeds and inflation pressures. The Tire and Rim Association has established these limits and publishes them in tables. They are also available through Goodyear and other tire manufacturers.
To determine what tire is needed, it is necessary to calculate the maximum expected loads at the wheel position. Then look at the tables, find the needed tire size, and match to a similar load, but slightly more than the maximum anticipated load.
Duals dominate the US market, so it's important not to mismatch tires when replacing a dual tire.
“If one dual is larger than the other, it will obviously carry more load and wear faster and unevenly,” says Cohn. “The smaller dual will also wear unevenly because it's forced to scuff over the road surface.”
If the tire size is 8.25R20 or smaller, the overall diameter of the replacement tire should be within a quarter inch of the original. If the tire size is 9.00R20 and higher, it should be within a half inch.
Another tire consideration is tread type. A block-type tread is good for traction on drive wheels, but it will increase the vehicle's rolling resistance and increase fuel usage. A tread should be chosen that best suits the terrain in which the vehicle is operating, and in the company's mileage goals.
Retreading tires is a way to cut overall tire costs. Tire casings, which can be recycled two, three, or more times, provide savings in a number of ways.
Retreading, new tires, pressure monitoring — and the management that is required to see they are properly utilized — can make the difference in a successful bottom line and one that is written in red ink. As expenses rise for fuel, insurance, driver recruitment and retention, and other fixed costs, getting the maximum service from tires can't be overlooked.
Goodyear offers tire tips
NO MATTER how carefully tires are selected, how they are treated will have the biggest influence on how long they will last. Here are five tips from Goodyear to extend tire life:
Check tire pressure daily using a gauge that's been calibrated from a master gauge. If dual rear tires are run, don't forget to check the inside duals.
Train drivers to accelerate and decelerate gradually. Quick starts and hard braking generate excessive heat, shortening the life of the casing.
Don't speed. For every mile per hour driven over 55 mph, tread life is reduced 1%.
Take it easy on corners. High speed cornering scuffs the tread, leading to premature wear and early tire removal.
Avoid hazards such as potholes, curbs, and rocks. Running over them can lead to irreversible sidewall damage and chunking.
Maintaining the proper inflation pressures shown in the load tables is critical. Each tire is rated at a specific load based on inflation pressure. The lower the pressure, the lower the weight it can carry. Underinflation also leads to higher heat, greater risk of premature tire failure, and reduced mileage.
Overinflating will give drivers an uncomfortable, bouncy ride, and the tires will develop excessive centerline wear, resulting in early removal.