Counteracting uneven wear on tires

February 2019

Paul Abelson


Q. You said you call people who write, to get details so you can answer. I have a complicated question about tires that I’d like to talk to you about. I’m getting wear streaks across my tires and I want to get rid of them. Also, I was skidding in the snow last week (early December) and that scared me. Please call.

A. You did have several situations going, and I was happy to review them with you. To correct uneven wear, find the cause and correct it, rotate your tires, and let normal driving remove the uneven wear. Do not, as your tire dealer’s mechanic suggested, turn down the tire on a lathe to get it round again. It’s an unnecessary cost that cuts tire life significantly, a cosmetic fix that does not correct the underlying problem. The uneven wear will recur.

Your wear problem may be caused by misalignment or improper inflation pressure, perhaps both. Alignment is easily checked and corrected as needed. There are two sections of the TMC Recommended Practices manual that will be helpful diagnosing uneven wear causes, RP216, the Radial Tire Conditions Analysis Guide and RP219, Radial Tire Wear Conditions and Cause. Both are illustrated to help us diagnose wear, and they recommend corrections.

Tire inflation affects tire wear. The old rule-of-thumb, keeping tires at 100 pounds per square inch (or 100 PSI) doesn’t work. It was instituted in the days when tires leaked air through the rubber, losing as much as 2-3 PSI per week. Speeds were lower. 100 PSI kept tires from getting too low. Low tires flex more causing added wear. With radial tires, high air pressure shortens the tread-road contact patch, increasing wear on the center of the tread. When pressure is too soft, outer edges tend to wear faster. Any misalignment adds to exaggerate irregular wear.

When radials get too low, about 20 percent below recommended PSI internal damage occurs, leading to tread separation. As proof, check those “road gators” along the road. If there are wires showing, these are not thrown retreads. They are the result of damage, most likely from under-inflation.

What is “proper” inflation? That depends on load, speed and tire size. For example, if you run at 80,000 pounds, you’re putting 34,000 on each tandem or 4,250 on each tire. You’ve been using Bridgestone 295/75R22.5 G-rated tires. According to their load tables, you should have 75 to 80 PSI in each tire. If you run the same size in H-load range, you’d need only 70 PSI. But for steer tires to carry 6,000 pounds each, you’d need 110 in each.

If you follow the “100 PSI all around” rule, you’ll be overstressing your steer tires and giving yourself a harsh ride from your drivers and trailer. Going low to put more rubber on the road the way the military does in sand and mud only works at low speeds. On highways, where snow may just be in scattered patches, you’ll ruin your tires and risk a blowout if you deflate them.

Tread depth is better for traction. If your tires are worn beyond 50 percent, say 15/32 in a drive tire that started at 29/32, you’ll be sacrificing a few percent in fuel economy but you’ll be gaining in skid resistance. Try to put newer tires on for winter and keep the well-worn ones for summertime. Automobile winter tires are made with rubber that is softer and more flexible in the cold. They don’t make them for trucks the way they do for cars. They would wear out too quickly in commercial service.

Thanks for a good wide-ranging conversation on an important topic.

Q. I have a 2016 International ProStar with a Cummins 450 engine. It has a fuel-water separator with the see-through bowl that I check daily. Lately, it’s been filling quicker, and sometimes there’s crud in it. That says bad fuel, but I’ve been filling up at only TA & Petro truck stops. Have they cheapened their diesel?

A. No. TA & Petro and all the other major fuel stops continue to maintain high quality standards in both their fuel and handling practices. At some truck stops that don’t pump the volume that the majors do, water can condense in storage tanks. If they buy from the day’s cheapest source, they may get a load that has been in storage longer than it should have been, or where costs have been cut by skipping over some fuel handling practices letting snow or rain water enter the fuel. Water in diesel is a life-supporting addition, but it’s not the kind of life we want. It’s algae and fungus, brought into the tank with air when the tank vents or fills. Water supplies oxygen and hydrocarbon fuel nourishes these unwanted creatures. They form the slime that plugs filters, blocks fuel flow and plugs injectors. That’s the crud you see in the separator bowl.

Here are some remedies. First, check your tanks for free water using a water-detecting paste on the end of a test stick or yardstick. If you find some, drain or siphon it from the tank.

Every fill-up, use a fuel additive that controls water. Some emulsify water, breaking it up into droplets so small they become harmless. Others de-emulsify water. They alter the fuel so it will not hold water. It drops to the bottom as free water to be removed. If you use a de-emulsifying conditioner, check for water regularly. Increase the normal dose for your first few fill-ups, but don’t exceed limits printed on the bottle.

Fill up often, even daily. This reduces the volume of air in tanks, reducing condensation.

Finally, use a biocide additive at least once a year. Biobore and Penray are respected makers, but not the only ones. Follow label directions completely. Biocides can be dangerous. LL

Paul Abelson, senior technical consultant, is a longtime contributor to Land Line. He’s a member of the Society of Automotive Engineers and a member of the Technology and Maintenance Council. In 1995, TMC awarded him its Silver Spark Plug award. In 2006, he received the Lifetime Achievement Award from the Truck Writers of North America. Although he’s “retired,” he still makes a popular contribution to Land Line readers with “Maintenance Q and A.”