Truck Management: Why tires fail

Ensuring proper tire inflation is, without a doubt, your best insurance against failure.
Proper inflation is even more important in construction applications – specifically on dump trucks – because the chance for overloading the vehicle is much higher than in on-highway or long-haul applications. “Dump trucks don’t go across scales very often,” says Guy Walenga, engineering manager, Bridgestone-Firestone North American Commercial Products. “And construction work generally goes on rain or shine. A dump truck full of dry material is one thing. But add water to the mixture and the same amount of material placed in a truck can dramatically overload that vehicle.”

Scrap pile CSI
If you’re suffering from a high incidence of catastrophic failures, Walenga says it’s a good idea to have your tire dealer send a rep out and inspect your scrap pile. With a little “CSI” investigation, that rep will be able to quickly identify gaps in your maintenance plan or operational trends that are prematurely shortening your tires’ lives.

“If I’m looking at a scrap tire, sidewall scuffing on a spent tire tells me that tire has been run with too-low air pressure for the load its carrying,” Walenga explains. “That’s because a tire’s sidewalls deflect a great deal more than they’re designed to.”

That deflection creates excessive heat – always a bad thing. And the sidewalls start to weaken as the heat and the increased scuffing take their toll. Over time, the tire will have more of a bulge to it every time it goes in and out of its footprint (the area under the tire when the tread – and only the tread – should make contact with the ground)
“If you look at that scrap tire’s bead, it’s often distorted out of shape – a sign of dramatic overload or under-inflation,” Walenga adds. “You can also look in the interior and in many cases the excess heat that gets developed from this excess deflection will show discoloration into the inner liner, and you may even see a breakdown of the inner liner components. So there are clues that if you know what to look for, you can put the pieces together and identify what’s going on.”

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The brunt of additional weight, compounded by the normal stresses of debris, uneven terrain and increased lateral stresses, has to be carried by the truck’s tires. Regular air pressure checks are important and can’t be replaced by visual inspections or tire thumping, notes Michael Burroughs, product manager for Michelin Americas Truck Tires. “Air can and will always escape from tires,” he says. “In fact, truck tires can lose about 2 pounds of air a month just from air diffusing through the inner liner and the casing. The resulting underinflation produces overloading, which results in excessive flexing and heat buildup – a major cause of tire blowouts.”

As a general rule of thumb, Burroughs says for every 10 percent a tire is below its fleet-specified pressure, the tire’s tread wear rate can increase by up to 15 percent. For example, a tire that is consistently 20 percent underinflated will lose 10 percent to 32 percent of its tread life – and that amounts to 45,000 to 80,000 miles depending on application.

To ensure proper inflation, Burroughs suggests the following procedures:

Always check inflation pressure when tires are cold. The best time to check is early in the morning. Even when outside temperatures are below freezing, heat generated during driving can temporarily increase tire air pressure above the recommended level.

Never let air out of a hot tire. This can result in dangerous under-inflation. Generally, lower air pressure is recommended during summer months due to expansion of air caused by heat. Higher pressure is recommended during winter due to air contraction caused by cooler temperatures.

Do pre-trip vehicle inspections that include cold tire inflation pressure checks. When performing these checks, don’t forget the inside tire in a set of duals.

Use a tire gauge that measures pressure in 2-psi increments. Check the gauge for accuracy periodically against a master gauge. Replace or recalibrate the gauge if necessary.

Use metal valve caps (or self-sealing nylon caps) since they contain a rubber gasket, which provides an airtight seal. Air-through valve caps can also work well and can encourage more frequent pressure checks.

Check the rear-inside drive tire. This tire is difficult to access and is overlooked typically when checking pressure. When the rear-inside tire is running flat, it quickly can develop zippers. Zippers are caused by broken cables in the sidewall and significantly reduce a tire’s life. New wide single tires, such as the Michelin X-One, remove the need for checking a rear-inside tire because it is no longer there.

Use the 10-psi rule – check your rear-drive tires frequently to ensure each tire is carrying its share of the load. All four rear tires in a dual tire situation should have identical pressures. If one tire is +/-10 psi, it will force the other tires to work harder and cause increased wear. Installing wide single tires will remove this worry.

Keep your tires aligned. Tires that aren’t aligned properly can experience rapid and irregular wear. It doesn’t take expensive machinery, however, to do a basic check of tire alignment. By rubbing your hand on top of the tire, you can tell easily whether your truck is experiencing a toe-in or toe-out condition. If your tires are aligned toe-in or toe-out, you will feel a condition called feathering (Tires in a toe-in condition will feel smooth as you rub your hand toward the engine. As you rub back toward the exterior, however, they will feel rough. This is referred to as smooth in, rough out. Tires in a toe-out condition will feel the opposite – rough in, smooth out. A truck running toe-in or toe-out will have feathered tires within 200 to 300 miles.)

Jobsites being what they are, tire failure is always going to be a part of your business. But a little attention to detail and the discipline to perform daily checks on tire condition and pressure, as well as debris avoidance and basic haul route maintenance, can go a long way toward optimizing the use of the second-highest-cost item on your company’s books.