Five tips to attaining optimal truck tire performance, service life
One thing is consistent when it comes to tire maintenance: Inflation has been, and always will be, a top concern for truck fleets. “It’s been talked about for as long as I’ve been around commercial tires, and that’s close to 40 years,” says Cooper Tire National Fleet Channel Sales Manager Jason Miller. “But keeping consistent inflation levels seems to be a moving target. When I’ve done yard checks with large fleets, I’ve seen the good and the bad. And, likewise with drivers. They have a huge impact since they’re supposed to check tires daily—with a gauge, not a thumper.
“The best fleets have tire inflation well under control, with drivers that are onboard with the need for accurate pressure checks, maximizing tire life and keeping costs under control. Since quality tires that are properly maintained affect longevity, driver satisfaction and fuel economy, inflation maintenance is a tremendous opportunity to reduce costs.”
What can be done to ensure a top-tier tire inflation program? Miller offers these tips.
Use calibrated gauges. “Every shop has gauges, and many drivers do as well,” he notes. “But the question is, are they accurate? Gauges get dropped, and even if they don’t look like it, they’re sensitive pieces of equipment. I’ve tested shop gauges against a master gauge in the past and have found psi readings can be off by 2 to 15 psi. If you’re not testing each gauge, and recalibrating them monthly against a master, there is a good chance you’re inflating tires to the wrong level. You should have a psi test station set up, along with master gauge in a highly visible area of the shop. Your techs and drivers need to use it. Some fleets simply have drivers swap out their gauges for a calibrated gauge once a month. You simply can’t have a good tire program if you can’t trust your gauges.”
Start with the chart. Like most major manufacturers, Cooper Tire provides load-inflation tables based upon Tire and Rim Association guidelines. “With a typical 6 x 4 legal load, there will be 34,000 pounds being carried by eight drive tires, or 4,250 pounds per tire. Using the table you’ll see that the drive tires can support that load at as little as 75 psi fully loaded,” Miller explains. “Yet, many fleets run a standard inflation pressure at 100 psi because, they tell us, ‘that’s what we’ve always done. It’s easy for our drivers to remember, and it gives us more margin for error if a tire leaks.’ So what’s the optimal pressure? Like so many things in life, the answer is, ‘It depends.’ Every tire has a personality. Likewise, every fleet has a personality. The most cost-effective tire programs come from matching the right tire to the right application at the right inflation pressure. It takes a little time and some discipline but the effort will pay off.”
“We need to think differently about air pressure,” he continues. “The reality is, the tire doesn’t actually support the load, the air does. The tire simply contains the air. Through inflation pressure, you’re primarily trying to manage two things: the shape of the tire footprint and the amount of sidewall deflection. Overinflation can pose several problems. The biggest is premature removal and ride disturbance due to irregular wear since you’re not getting the optimal footprint patch to the road. With the weight concentrated on a relatively small contact patch in the crown of the tire, the shoulders will scrub their way into and then out of the contact patch causing rapid and uneven edge wear. You’re also likely to see significant heel-toe wear and increased, ‘road rash’ or chipping of tread rubber in the center ribs. The resulting ride disturbance and general ugliness often result in early removal despite having as much as 30 to 40 percent useable tread remaining. These problems are especially prevalent in mixed service applications running open shoulder drive tires. Next, with such a small contact patch, you’re compromising traction, and that really comes into play, not only in winter but in muddy off-highway operation. You may also see an increase in the occurrence of impact breaks since the tire sidewalls have less flex. Finally, you’re impacting fuel economy. I always tell fleets that they need to break the cycle and run tires at their proper inflation level. Only then can you get the true performance engineered into the tire, and that will pay you back in the form of a lower cost of ownership.”
What’s the impact if you don’t follow the chart? “Big,” Miller affirms. “While operations vary significantly, running tires that are just 10 percent underinflated may cause you to remove them from service 10 percent early. At 20 percent underinflated, tread life may be reduced by as much as 25 percent.”
Audit your inflation levels. Yard checks are a pain, but a necessary evil. “If you’re serious about getting your tire costs in check, you really need to benchmark where you’re at with tire inflation, and identify problem areas,” Miller notes. “Only then can you take steps to improve your program. For example, what percent of your duals—both on your tractor and trailer—have inflation pressures within 5 psi of each other? Did you know that just a 5-psi difference in inflation between duals is the equivalent of one tire having a circumference that is 5/16-inch smaller? That means during every rotation cycle, the smaller circumference tire must scuff ahead to keep up with the tire with more inflation. These tires rotate around 500 times per mile, so simple math means 500 multiplied by 5/16-inch translates to 156.3 inches per mile, or 13 feet per mile. Imagine dragging a tire 13 feet every mile, under load. How many feet is that per day or per year? That illustrates clearly why you will see increased tire wear with improper pressure.”
Tire related concerns beyond air pressure. “Another area to watch is with retreads,” he adds. “It’s back to circumference. In some cases, fleets will get identical retreads back from their retreader, but the casings may be different. Each brand and model may have a slightly different diameter so, while two tires will look identical when you get them back from the retreader, one may be significantly taller than the other. This is why we recommend using a circumference band, good measuring tape, or have a height gauge mounted in the shop to check circumference. Otherwise you may be putting together duals that should be identical, but are really mismatched in height and that will cause one tire to wear prematurely.”
Incentivize drivers. With today’s advanced trucks, it’s possible to gauge how well a driver works the truck—hard braking, quick starts and fuel economy can all be logged and analyzed. “Many fleets provide bonuses for drivers who practice less aggressive driving and take an active role in proper tire inspection and maintenance,” Miller observes. “We’ve seen progressive fleets offer bonuses for tire wear and proper tire inflation. And why not? If the driver keeps tire inflation at the proper level, and does fingertip diagnostics on each tire during pre-trip inspections, tires will have longer lives. How drivers take care of their tires can be easily tracked when the truck returns to the terminal.”
If these tips are followed and operators run the correct tires for their applications, fleets stand a solid chance of pulling the drive tires at 2/32nds, and the steers at 4/32nds. “And your casings should be in great shape for retreading,” Miller concludes. “The way to extend your budget on tires is to get the most miles, coupled with the most retreads. Proper tire selection is one key to doing that, but it’s the maintenance practices—especially proper tire inflation—that keeps your tractors and trailers operating as efficiently and safe as possible.” — Cooper Tire & Rubber Co., Findlay, Ohio, 419/423-1321, 800/537-9523; www.coopertire.com