Tire-related problems are the No. 1 reason for tractor-trailer downtime in the U.S. Every tractor-trailer combination has 18 opportunities to fail. En route tire failures most often are due to tire punctures, sidewall damage and runflats. Such delays result in 2.5 hours of vehicle downtime on average.
This may seem obvious to some of you, but to my great surprise, fleet managers attending the annual meeting of the American Trucking Associations' Maintenance Council in March rated a session titled "Tire Maintenance: Mastering the Basics" as the best held at the meeting. Apparently it reminded them of things they had long forgotten.
The program presenters were Guy Walenga of Bridgestone/Firestone Inc., Kevin Rohlwing of the International Tire and Rubber Association, Al Cohn of Goodyear and Trent Longo, Hercules Tire & Rubber Co. They each touched on the basics of tire maintenance, from selection to computing cost per mile.
The following summarizes Al Cohn's presentation on optimizing tire performance.
One of the questions fleets ask most frequently is: "How important is it to maintain the proper tire inflation pressure?" The answer is: It is vital.
Tires require the proper inflation pressure to carry the vehicle load. If you run overinflated, drivers are not very happy because they will be bouncing all over the highway. In addition, the tires will develop centerline wear and will be removed from service prematurely.
If tires are run underinflated, nothing but trouble can result. Underinflation causes irregular wear, shortens casing life and also increases the likelihood of tire punctures.
Underinflation also reduces removal mileage. A tire that is 20-percent underinflated will lose 12 to 16 percent of its potential tread mileage. Fuel economy also will be reduced. A general rule of thumb is that for every 10 psi of pressure loss, a 1-percent drop in mpg will result.
We all know that tire air pressure should be checked when the tires are cool—not when they've just come in off the road and still are hot. It's also important to gauge tire pressure when the temperature outside is moderate.
Ambient air temperature affects tire pressures. A tire that is inflated to 102 psi at 65 degrees Fahrenheit will increase in pressure to around 110 psi at 100 F. While altitude also has some affect on air pressure, it is a small one. Pressure will increase about 2 psi for every 5,000 feet of altitude.
Instead of worrying about these factors, it is more important to worry about checking air pressure frequently. How often is frequently? Goodyear recommends checking air pressures once a week for line-haul fleets, assuming drivers are looking at their tires daily for punctures, snags etc.
If a fleet runs a lot of city driving or secondary/off-road operation, then air pressure should be checked more often.
The most important things are to: 1) make sure the pressure gauge is calibrated; 2) never check a hot tire; and 3) don't forget to check the inside dual tires.
Dual tires should be mated within 1/4-inch overall diameter if the tire size is 8.25R20 or smaller, and within 1/2-inch overall diameter if the tire size is 9.00R20 or larger. Improperly matched duals are subject to rapid treadwear, because the larger tire carries more load and will wear faster and unevenly. The smaller tire also will wear unevenly because it is forced to scuff over the road.
Most fleets have found that balancing steer tires significantly reduces driver complaints due to tire vibration issues and decreases the amount of irregular wear that may develop in slow-wear-rate operations such as line-haul service. Balancing drive and trailer tires has not been a practice adopted by many fleets.
The best time to remove steer tires is when the remaining tread depth is between 6/32nds and 8/32nds of an inch. Drive tires should be removed at 6/32nds to 8/32nds in mixed service applications, where stone-holding and drilling is a problem, and at 4/32nds to 6/32nds in strictly highway-service operations.
If the fleet owns its own trailers, the tires from these units should be removed at 3/32 to 4/32 inch. A good practice is to retread original steer, drive and trailer tires to drive designs as retread No. 1 and then to trailer rib designs as retread No. 2. For fleets that don't own their own trailers, original tires can be retreaded to drive designs as retread No. 1, removed at 6/32 inch, and retreaded again with a drive design as retread No. 2.
According to The Maintenance Council's recently adopted "Recommended Practice on Alignment," a new vehicle should be checked for proper alignment no later than 90 days or between 15,000 and 30,000 miles after going into service. Toe, camber and drive-tire thrust angle should be checked. On average, fleets that have not been aligning their vehicles can expect a 30-percent increase in tire mileage when seriously carrying out such a program.
Total-vehicle alignment includes the trailer, too. A fleet may have a great tractor alignment program but realize little gain in tire performance if its trailers are out of alignment and going down the road sideways. Trailer misalignment can result in a 30-percent reduction in mileage.
Speed also affects tire performance. The faster a vehicle goes, the hotter the tires become, and heat is a tire's worst enemy. Retreadability, fuel economy and removal mileages are reduced in high-speed operations.
For every 1 mph over 55, fuel economy is reduced by 0.1 mpg. Going from 55 to 75 mph decreases tire removal mileage by an average of 30 percent, and a 2-mile-per-gallon drop in fuel economy also can be expected. (This is about 33 percent of a typical fleet's fuel consumption of 6 mpg.)
So to optimize tire performance and reduce tire costs, fleets should:
Check air pressure on a regular basis with a calibrated gauge;
Mate dual tires properly;
Balance steer tires;
Implement a good casing management program to maximize mileage and retreadability;
Align both tractors and trailers; and
Keep vehicle speeds in check.
So, did you pick up any little tidbit here that you didn't know before or had forgotten?
Armed with some of these facts, you now can charge off and impress your fleet accounts. If you can get them to actually do these things, you'll save them loads of money in tire and fuel costs.