Feature Article: Seven tire killers

John Baxter | May 03, 2010

Seven tire killers

 

 

Tires, your biggest variable cost after fuel, cost a lot less per mile if they last as long as intended. Experts weigh in on the biggest threats to your tires.

 By John Baxter


 

 

 

1 Underinflation

A tire running on low air works “harder than it was intended to work. The tread rubber heats up,” says Guy Walenga, director of engineering for commercial products at Bridgestone/Firestone. Furthermore, the potential damage accelerates the further the tire gets from optimum pressure. For example, running 10 percent low means much more than a 10 percent increase in flexing, heat and damage from bending the steel cords beyond the point where they will spring back.

“You can never repair damage done to a tire this way,” Walenga says of overflexing. And “there is no tell-tale sign of damage. It may end up being useless for retreading.”

It also might be useless long before retreading. “Any commercial tire that has been run more than 20 percent underinflated must be considered flat and removed from the wheel to be inspected for damage,” says Matt Gudermuth, Continental Tire’s warranty manager for commercial vehicle tires. “Circumferential fatigue ruptures, known commonly as zipper failures, are caused by extreme deflection of steel casing cords during the load cycle of rotation, when the tire is underinflated or overloaded.”


 

 

 

 

 

This rupture results from excessive flexing and heat from underinflation or overloading. Not only do the steel cords bend beyond the point where they can easily spring back, but the heat weakens them and the other parts of the casing’s structure.

2 Overinflation or overloading


Overinflation can happen in these ways, says Jones:

• You put a significant amount of extra air in the tire to compensate for leakage. It’s always better to fix the leak and inflate the tire up to the proper pressure.

• You air the tire up on a cold morning and end up driving at high speeds after the weather warms significantly. Take time to check pressure in this situation and adjust as necessary.

• You’ve aired your tires for 80,000-pound running and then start hauling lighter freight. Instead, reduce the pressure according to the manufacturer’s recommendations for the axle loading.


When an object gets pinched between duals, it can damage the sidewalls enough that the cords and other parts of the casing are weakened and the casing made unrepairable. A regular tire inspection program that includes removal of such foreign objects will help with this problem.

3. Poor wheel alignment

“If the tires are not rolling straight down the road and straight up on the road surface, they are going to wear faster or in some sort of uneven way,” says Goodyear Marketing Communications Manager Tim Miller. “Today’s radial tires are designed to run such long distances before they wear out, any issue with toe, camber, caster and all axle perpendicularity to the chassis centerline will have a marked, negative effect.”

Getting wheels aligned “is one of the best ways to spend your maintenance dollars,” Walenga says, “Misaligned steer tires will wear prematurely, especially when toe-in is way off. This can happen to the point where the treadwear cuts into the casing and even the cords, so the steel is gone. At this point, the tire is nothing but scrap.” An inspector will write you up, too, for a tire sustaining such damage.

While toe-in is the most important setting and the one you need to check and reset most frequently, total vehicle alignment – aligning the trailer, drive and steer axles at an appropriate mileage – is just as important. For example, a trailer that’s “dog-tracking,” or running with the rear to one side, will wear the tires on the tractor, too. Consult with your tire dealer or a quality alignment shop about appropriate intervals for your application.


4 Poor suspension maintenance

Normal suspension component wear will result in a need for periodic alignment. However, neglect of the suspension system will create a snowball effect, with the tire facing uneven stresses that change every few seconds, as well as a suspension system that simply cannot be brought to spec.

Says Miller, “Steering system, suspension and wheel end maintenance … periodic checks for tie rod end looseness, worn king pins, wheel bearings and shock absorbers are essential. Any of these components that are worn out will kill tire wear in two ways. First, it is impossible to do a proper alignment of axles (including toe, camber and caster) without the components being up to snuff.

“Second, looseness or a compliant component that should be rigid in any of these systems will create irregular wear conditions that are usually irreversible once they start.” In other words, when tread wears in a certain, irregular pattern, conditions are created that make that wear spread because the tire can’t roll smoothly and with all the tread rubber taking equal loads.

Key suspension maintenance activities include frequent greasing, at least twice every oil change, with the grease specified by the component manufacturer, and frequent inspection of tie-rods, king pins, suspension bushings and the like for looseness.

Also, replacing shocks whenever they fail to maintain a stable ride will eliminate uneven tread wear, while also preserving the life of all the chassis components and making the ride more comfortable.


5 Improper mounting and de-mounting

“I’m sure we’ve all seen YouTube videos of Arctic race teams mounting tires with starting fluid,” Gudermuth says, referring to spraying ether inside the tire and igniting it to blow a tire onto the rim. “Even if the tire survives the mounting process, it can easily damage the liner, leading to failure in service. The more immediate concern is detonation of the tire through the burned body ply, or from explosive accumulation of pressure in the wall of the casing.”

This mounting method isn’t the only foolish technique that has been around for years. Using improper tools with rough edges that pry too hard and damage the bead is a common one. Instead, use a tire mounting/demounting machine or tools designed to protect the bead from concentrated force.

For mounting, “You need a clean and round wheel,” meaning one that has never been damaged or over-stressed, Walenga says, “and the tire must be properly mated to that wheel.” The rim needs to be clean, so grit or dirt won’t keep the tire from sliding on properly in one area.

To check that mounting is even, look for the guide rib, a thin line on the outside of the tread. It should be an even distance from the outer edge or flange of the rim all the way around. This requires good mounting technique, plus the use of the proper lubricant on the rim and bead. Check both sides.

Walenga stresses the need to check the tire stem when remounting. Replace the core seal, which unscrews, rather than re-using the old one. The cap is supposed to be the primary seal, so replace that, too. The smartest procedure is to install a flow-through design that seals but also allows the driver to check pressure and put air in the tire without removing the cap.


Failure to seal the inner liner after the tire is punctured will allow moisture to penetrate the casing and rust the steel cords, which causes them to fatigue and break after mileage is accumulated.

6. Improper repairs

A rope repair is a simple way to plug a puncture from the outside, but it often causes air to penetrate the belts, pushing them apart. Merely plugging a hole can also allow moisture from inflation air to get into the cords, and corrode them, creating a catastrophic failure later.

“Besides the danger of running a damaged tire without inspecting the casing, rope repairs cannot withstand the air pressures required by commercial steel cord tires,” says Gudermuth. Plugging a hole in the “no repair zone” of the shoulder is a big no-no, he says. “Quality repairs are a bargain compared to compromising road safety or damaging the vehicle.”

While some forms of tire plugs may be satisfactory just to get you home, the tire must be shortly thereafter removed and inspected, Walenga says. The inner liner must be resealed – from the inside – before it can be considered safe for long-term use or casing re-use during retreading. Gudermuth says, “Even a properly repaired tire must be carefully inspected for damage to the steel casing cords and reinflated by trained service personnel.”

In this zipper failure, the gash is wide and the cords are completely separated. Such a tire can explode and seriously injure the person installing it.

The repair materials must be fresh, Walenga says. Tire sealants, patches and vulcanizing cements must be compatible with one another, so use only materials from the same manufacturer. The tire must undergo a full inspection inside and out, too, or you’ll never be safe or be able to count on retreadability.


7 Tire unsuited for the application

“My bicycle tires do a great job on my bike,” says Miller, “but they wouldn’t make it on a working truck. Today, all tire manufacturers make specific tires for specific jobs. There are steer axle tires, drive axle tires and trailer tires.”

Truck tire repairs must not be done with rope type material as it cannot contain the inflation pressures for such tires. This repair was made in the shoulder of the tire, which is not fully reinforced by belts. Air leaked in around the repair and separated the cords, resulting in a potential for catastrophic failure.

There are tires made for on-highway applications and off-road tires. “We have tires for regional service that are better for high-scrub applications and some that are for service a little closer to long-haul,” he says.

All manufacturers rate their tires as to suitability for position and application. Only a few tires are designed to work in more than one position or application.

“The wrong tire or tread will not be as durable,” says Walenga. “They won’t die suddenly, but carefully matching the tire and tread pattern to the job and position will help extend a tire’s life significantly.” n


 

Other deadly tire issues

LACK OF A FORMAL INSPECTION PROGRAM. Regular inspection will enable you to fix problems before they cause irreversible, irregular wear or other damage. For example, an object lodged in the tread, if caught early, might not ruin the casing. Also, Goodyear’s Tim Miller says, “The wear pattern of a tire is a great insight into the state of alignment and steering systems, suspension and wheel ends.”

BRAKE HEAT. This comes from an improperly maintained, unbalanced brake system, says Michelin’s Doug Jones, often because stopping duties are not equally shared by all wheels. To prevent this, do brake jobs thoroughly, replacing all parts with new ones from a quality rebuild kit. Make sure all relay valves have identical crack pressures and response curves by using parts that meet manufacturer’s specs. To prevent overheating the wheels on extremely long grades, stop and allow brakes to cool, or stay at a low speed.

FLAT-SPOTTING. This is a major worry when one or more wheels lock up. Maintaining the braking system so all the brakes work in unison will help prevent flat-spotting, which is common on trucks still utilizing non-ABS brake equipment. Control the treadle valve and apply pressure when braking hard with such equipment, responding to lockup by backing off. On most modern vehicles, keeping up with ABS maintenance by responding immediately to any trouble codes from the system will prevent tire flat-spotting.

CURBING IN TIGHT QUARTERS. Curbing the tire in city environments can be avoided by remembering to swing wide enough to the left on right turns so the shorter wheelbase of the tractor doesn’t cause the trailer tires to roll over the curb. The longer the trailer, the wider you need to swing.

IMPROPER RETREADING. Retreading is best done by a shop that has sophisticated casing inspection equipment and well-trained inspectors. Every step of the process, whether installing a hot cap or pre-cured new tread, must be precisely controlled and verifiable. If possible, find customers of any given retreader and ask about their experiences with the tires.



Alignment terms

TOE. Toe or toe-in refers to the angle between the front wheels when viewed from above. The tires normally are slightly closer together in front when at rest to compensate for rolling resistance.

CAMBER. Wheels are set almost vertically, but given a slight camber angle to make steering more stable by helping keep the tread flat on the road when the cab leans in corners. This setting is normally designed into the front axle.

CASTER. This is the angle of the kingpins from vertical. Proper caster helps ensure stability by generating a force that tends to return the steering to the straight-ahead position.

STEERING AXIS INCLINATION. The need for the outer tire to turn to a sharper angle than the inner tire when the truck is turning. This helps avoid scrubbing.

PERPENDICULARITY OF AXLE. Having the axle at exactly ninety degrees to the tractor or trailer chassis centerline so that it will roll straight rather than generating a side force.

Overloading a tire produces problems similar to those of underinflation, says Doug Jones, Michelin’s customer engineering support manager. Never load a tire beyond its rating.



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