Where’s the Wear?

Feather wear causes one side of the tread rib to be higher than the other, resulting in step-offs you can feel from one side to the other. Feather wear is caused by side scrubbing, usually the result of excessive toe-in or toe-out, or severe drive axle misalignment.

One goal of tire maintenance is to have the entire tread surface wear out at the same time. As soon as tread wears too much in one place, it has to be replaced.

Irregular wear is most common in over-the-road driving, where tires have plenty of opportunity to wear down, says the Bridgestone/Firestone video Saving Through Reducing Irregular Wear. Irregular wear can occur for several reasons, such as uneven seating of the rim on the wheel, imbalance, bad shocks or panic stops that lock the wheels. Once this wear starts, it makes the tire bounce, which makes the wear continue.

Not only your eyes, but your fingertips can help you read tread condition and pinpoint the problem, whether it’s incorrect inflation, misalignment or something else.

One type of irregular wear occurs because the weight of the truck is not evenly distributed on the tread, such as when the tire is leaning to one side from improper suspension camber. The other type occurs when the wheels are misaligned, meaning they’re headed down the road in different directions. When one or more tires are not aimed straight ahead, they produce side forces, meaning the tires scrub the road while rolling. A 2-inch misalignment on a truck with a 181-inch wheelbase would create the same wear as having the tractor dragged 58 feet sideways every mile.

When you rub your fingers across a tire that’s scrubbing, it will feel rough in one direction and smooth in the other because the bands of tread are worn more on one side. This almost always means side forces are at work.

When the front wheels have toe-in, they are turned inward, so that their forward edges are closer together than the back ones. The tread will feel smooth when moving inward toward the center of the truck, while it will feel rough or feathered when moving outward.

With toe-out, the rear edges are closer together than the forward ones. The tread will feel smooth when moving outward, and rough moving toward the center of the chassis. Toe-in or toe-out can be caused by incorrect settings in the front suspension, or problems with the Ackerman angle, which is the turning angle needed to negotiate a corner or curve without scrubbing.

Proper alignment is also critical. You can figure out how frequently to align your equipment by referring to Guidelines for Total Vehicle Alignment, Recommended Practice 642, from the Technology and Maintenance Council of the American Trucking Associations. Aligning on a schedule rather than waiting until you notice irregular wear will save you plenty. Also align whenever replacing tires.

Think of the vehicle as a whole when doing alignment, says Doug Jones, a support manager for Michelin. Making sure the alignment settings are in the middle of recommended ranges, not just within maximum tolerances, will further improve performance, say Bridgestone/Firestone materials. Maintain suspension systems and replace worn parts regularly.

Alignment is often thought to be a front end problem because the front axle does the steering and has the most wearing parts. In fact, the most common truck alignment problems are drive axles misaligned with each other and with the front axle. The second most common problem is trailer axle misalignment.

To be aligned properly, a tractor needs to be put on a large alignment rack so all the axles can be put in line. If you regularly pull the same trailer, its axles should be set at the same time.

Also consider these factors to minimize irregular wear:

INFLATION. This is the top tire maintenance issue, says Al Cohn, technical marketing manager at Goodyear. “Don’t forget that just gauging tires isn’t enough,” he says. “You have to replace or recalibrate old gauges, too.” Too many truckers don’t even recalibrate gauges after dropping them, Cohn says. Goodyear recommends checking inflation once a week. Because pressure should vary with load, refer to a load chart, such as one at this site.

SELECTION. “Irregular wear is often a sign that you’re using the wrong tire for the job,” explains Real Questions, Real Answers, a Bridgestone/Firestone booklet. It recommends that linehaul trucks use a tread with straight grooves and sipes, which are tiny slits; for off-road use, zigzag grooves without sipes may prolong life. Zigzag design gives more surface, spreading out abrasive forces.

Inappropriate tread compound also can create irregular wear. For example, a tough, scrub-resistant compound works well in pickup and delivery service, but a compound that runs cooler will give more regular wear in highway service.

MOUNTING. Make sure tires are mounted evenly all around (evenly seated on the bead) and properly balanced. Goodyear recommends mounting so the low spot marked on the wheel lines up with the high spot marked on the tire to help balance each wheel/tire fit. Manufacturers and tire service technicians can highlight the marks.

SPEED. If it’s practical, reduce your top speed to prevent heating the tires excessively. Slowing from 75 mph to 55 mph extends tire life 20 percent, Goodyear says.

RECORDS. Keep detailed records. For example, if you rotate tires to minimize the effects of irregular wear but notice a problem keeps appearing at a certain wheel position, you can better focus your troubleshooting.

Proper alignment and inflation reduce tread wear, improve casing retreadability, greatly improve fuel economy, reduce driver fatigue and improve driver satisfaction. Practice these basics, and the stories you read from your tires will have happy endings.


7 SOURCES OF TIRE WEAR

Here are some of the chief causes of uneven stress that produce irregular tire wear.

  1. THRUST ANGLE. With a misadjusted thrust angle, the drive axles will be almost parallel with one another, but not aligned properly with the chassis and front axle. The entire chassis will roll down the road at an angle. To detect misaligned thrust angle, “You’ll need to look at two tires,” says Goodyear’s Al Cohn. Tread wear will be similar to toe problems except that the wear pattern on one side of the chassis will feel like toe-out, while on the other it will feel like toe-in. You’ll eventually see fast wear on the outside on one side and fast wear on the inside on the other.
  2. SCRUB ANGLE. When the drive axles are fighting each other but the angles average out close to the correct alignment, the scrub angle is misadjusted. You’ll see just a diagonal wear pattern on the drive axle tire treads. Axles that shift around because of loose or worn axle components also will cause this tread wear pattern.
  3. DOG TRACKING. When either drive or trailer axles are out of line, you have dog tracking. The trailer does not follow straight behind the tractor. You might see more of the trailer in the mirror on one side than on the other.

    How do you know whether a thrust angle or dog tracking problem comes from misaligned drive axles or trailer axles? Evaluate the driving symptoms. If the truck pulls constantly to one side, the problem is in the mounting of the drive axles. If it wanders and you need to crank the wheel in both directions to keep it straight, it’s the alignment of the trailer axles.

  4. INFLATION. “With underinflation, the center of the tread lifts up off the road,” says Michelin’s Doug Jones. “You’ll get wear on both shoulders.” With overinflation, “The center ribs will move outward from the center of the wheel. Then, the shoulders will show good wear, while the center of the tire will show high wear.”

    Severe underinflation can produce “low and high lugs all around, a kind of funny, erratic wear that’s all over the place,” Cohn says. With overinflation, “you’ll get centerline rib wear, so the center rib becomes depressed compared with the others.” Underinflation, the natural consequence of normal leakage without proper maintenance, also produces severe overheating of tires.

  5. CAMBER. “Positive camber” happens when either improper manufacturing or severe overload causes an axle to bend downward in the middle. This causes the tires to tilt, running far apart at the bottom and too close together at the top. You’ll see wear on the inside shoulder on both sides. The tire will feel much as it does with toe-in wear, Cohn says.
  6. CUPPING WEAR. This produces bands of high wear at various locations. “The tire is shimmying relative to its axis,” Jones says. Cupping occurs when the tire is not evenly seated on the rim, which means its diameter is not the same all the way around. It also can be caused by imbalance, bad shock absorbers, loose or worn suspension bushings or misadjusted air springs. Cupping often starts at one location and then spreads around the tire.
  7. FLAT SPOTTING. This occurs when a driver locks up the wheels because he doesn’t know how to modulate the brakes or the ABS isn’t working right. It starts as a single, flat, scrubbed band of shallower tread running across the tire. It, too, can spread cupping wear around the tire because of the vibration it creates. Having ABS and keeping it in good shape helps eliminate flat-spotting. Specifying an ABS system with more channels also helps.

  8. FROM BALLS TO BEADS: THE QUEST FOR BALANCE
    An old trucking myth says if you put three golf balls into a tire, they will shift around until they balance it out. While that procedure doesn’t meet the approval of tire makers, other companies have applied the concept by using tiny balancing beads.

    Balancing beads are sold in some Goodyear tire centers, says Goodyear’s Al Cohn. “Some people like it; some say it does not work and continue to use lead weights,” he says of the weights locked onto a rim after a tire/wheel combination is spin-balanced. “We sell it, so we think there is some merit there.”

    One such product, Counteract Balancing Beads, is said to “automatically counteract the imbalance” of a tire. The glass oxide beads have a tiny bit of silicone added to make them flow easily around the tire.

    Another product, Equal, consists of tiny grains of a “dry granular polymer from the plastics family,” says Bob Fogal Jr., president of Equal maker IMI. “It’s compatible with all tires and wheels and dampens vibrations effectively because it’s manufactured so it consists of varying particle sizes.”

    Testing the product on heavy truck wheels at the independent Transportation Research Center showed that it does indeed do its job, Fogal says.

    Keith Harring, whose K.L. Harring Transportation runs more than 30 Kenworth tractors, swears by Equal. He claims one truck with 380,000 highway miles on it has 8/32-inch to 10/32-inch left on its original rubber. The fleet’s maintenance manager, Tommy Vajdic, says Equal “prolongs tire life and keeps the drivers happy.”

    The tire sealant Ride-On is also marketed for its balancing properties. Ride-On, a liquid, is pumped in through the valve stem.

    Equal and Counteract beads are added to the interior of the tire by simply tossing in a small bag that later disintegrates.


    RESOURCES
    Bridgestone/Firestone
    (800) 367-3872
    www.bridgestone-firestone.com

    Michelin North America
    (800) 847-3435
    www.michelin-us.com

    Goodyear
    (330) 796-2121
    www.goodyear.com

    Toyo Tires
    (800) 678-3250
    www.toyo.com

    Technology and Maintenance Council
    (705) 838-1763
    www.truckline.com

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