The tales tire treads tell
Look what’s happening, find out why, and correct it.
Tires are a major expense, probably No. 2 or 3 on your list, after fuel and, of course, paying yourself. Just one tire costs $400 or so. The longer it lasts, the less it costs on an annual and per-mile basis. Conversely, neglect makes tires more expensive. During pre-trip and post-trip inspections, look closely for irregular tread wear patterns. If you find them as they start, you’ll have more time to correct the causes.
Over the years, members of the Technology & Maintenance Council of the American Trucking Associations have studied irregular tire wear, beginning with the old bias-ply tires and now with radials. Members are fleet managers and tire-manufacturer representatives who constantly deal with wear problems, and they’ve catalogued them in their Recommended Practice 219D (now in its fourth version). This RP lists 33 wear patterns among steer-, drive- and trailer-axle tires.
It also lists causes, which tend to repeat themselves.
Improper alignment and underinflated tires are major causes of irregular tread wear, according to Peggy Fisher, a long-time TMC member and former general chairwoman. She’s specialized in tire maintenance for many years. She managed the tire program for the old Roadway Express, has been a consultant and now is president of Tire Stamp Inc., a high-tech tire management service.
“It’s not uncommon for a truck to come from the factory out of alignment,” Fisher said. “And if drivers feel a tractor pushing in a way other than straight, it could be trailer or drive axles. If they own a trailer, they should have both the trailer and the tractor aligned. They should do an alignment on their trucks once a year, and more often if they feel it pull” one way or the other.
Improper tire pressure is perturbingly common, and there’s no cheap or easy way to remedy it, she said. It either involves special equipment or considerable effort on the part of drivers. A good gauge and an air hose allow a driver to check and correct pressure, but servicing the 18 tires on a typical big rig takes time. (Tip: To eliminate hunting for an air supply and maneuvering the rig to it, keep a tire hose on board and hook it to an air tank with quick-connect/disconnect hardware.) Aside from the manual method, pressure can be maintained by several automatically operating products, though they cost money and themselves require some maintenance. More products are available for trailers than for tractors, whose drive axles complicate mounting, and only one device we know of works on steer tires.
Steer axle tires are critical for safety, because a blowout can send you and your truck into a wall or ditch or, God forbid, into other nearby vehicles. (It doesn’t have to: At the sound of a front tire blowing, step hard on the accelerator and keep going. Steer the truck to a safe place, even if it’s a ways down the road. Then slow down gradually and park. It works.) Even tread wear is what you want no matter where the tire is on the rig, but irregular wear can result from a number of things. Usually you can continue running an oddly worn tire, either where it is or at another position on the vehicle. If its overall tread is shallow, replace it or, if its casing is healthy, have it retreaded.
Some conditions have simple causes, like toe-in and toe-out wear on the inside or outside of the tread. This is from misadjustment of toe settings on the front wheels, a relatively easy fix. Other conditions can be complex, like scrub/thrust angle-induced full shoulder wear (even the term is complex). This can come from misalignment of drive or trailer axles (they’re not perpendicular to the frame), or a dry fifth wheel, which impedes turning and tries to push the tractor straight ahead. Grease the fifth wheel, or get all axles realigned. TMC identifies 13 wear conditions for steer tires. Fisher pointed out the four most common ones.
Shoulder step/chamfer– A step is worn on the edge of the tread and completely around its circumference. It can be on one side or on both sides. If on both sides, the step on one side is wider than the other. This can be common on tires without “defense grooves” along tread edges and when wear is gradual.
Feather wear – Each rib is individually worn toward one edge, giving a high-to-low appearance. The main cause is excessive toe-in of the front wheels, but other possible causes are damaged suspension parts, such as bent tie rods. If feather wear appears on both tires, drive-axle misalignment can be the cause.
Cupping/scallop/wavy wear– Tread is scooped out in alternate areas of the tread’s edges, creating a scalloped look, and sometimes progressing across the entire tread. Blame it on an unbalanced tire-wheel assembly, lack of shock absorber control, loose kingpins, and/or improper bearing adjustment.
Rib depression/punch wear – Inner ribs worn lower than adjacent ribs around a tire’s circumference. The primary cause is low air pressure. Other causes are improper seating of the bead on the wheel, bad shock absorbers, and improper bearing adjustment and bad tire-wheel balance.
Power and torque coursing through drive axles subject these tires to high stresses. Big-power diesels have prematurely consigned countless tires to their deaths. And you know what happens when wheels lock up and tires acquire brake skid patches. Sometimes it’s so severe, as when wheels are dragged long distances, that it ruins the tires. New linings and improper brake adjustment are the usual causes, but aggressive braking can also cause it. (You wouldn’t do this, would you?) You might have seen and complained about overall fast wear, which can be caused by abrasive pavement surfaces, high loads, frequent turning and braking, and simply the wrong tire and tread for the application.
RP 219D lists six drive-tire wear conditions, and Fisher says these three are the most frequently seen:
Rapid shoulder wear, one side – Excessive wearing of the inner edge of the inner dual or inner edge of a wide-base single tire. Caused by negative camber of the wheel (the top of the tire-wheel assembly is closer to the truck’s frame than the lower portion) as a load bears down on it. It can be aggravated by air suspension flex, ultradeep tread depth, and uneven inflation pressure in duals. A wide-base single tire can show rapid shoulder wear on both sides, usually caused by overinflation.
Shoulder step/chamfer wear – Tire worn on the edge of a shoulder, usually starting on the inner edge of the inside dual on the forward drive axle. This is typical of radial tires but might vary with tread design and service application. Improper inflation, worn or damaged suspension parts, and road conditions are among aggravating factors.
Heel/toe wear – Each lug around a tire worn high to low from front to back edges. Mismatched inflation and tire diameter are among the causes, but high engine torque and running on mountain roads can be factors.
The trailer carries the payload, but there’s no pay until you deliver the load. That will be delayed if a tire fails en route. So, whether the trailer belongs to you or someone else, its tires need proper inspections and decent care. TMC identifies 11 tread wear types, and the most common are these.
Diagonal wear – A series of flat spots appear diagonally across the tread at 25- to 35-degree angles. Caused by improper bearing adjustment, toe out, mismounting of the tire-wheel assembly at the lugs, or mismatched duals. It might start as a brake skid or other irregular wear pattern.
Multiple flat spot wear – Numerous areas worn flat around the tread’s circumference. With duals, it’s caused by mismatched inflation pressures or height of the two tires, improper bearing adjustment, imbalance, bad shock absorbers, or driver abuse of the trailer brakes. This, too, is aggravated by high-speed empty or light-load running.
Cupping/scallop/wavy wear – Cupped-out areas creating a scalloped appearance around the tread’s circumference. Usually caused by out-of-balance wheels and tires, bad mounting, bad shocks, improper bearing adjustment, or underinflation.
Erratic depression wear – Random wear spots around the tire’s circumference. Caused by bad shocks, mismatched tires or inflation pressure between two duals, improper bearing adjustment or bead seating, and tire-wheel out-of-balance. High-speed light-load running aggravates it.
So, next time you’re out on a lot kicking and eyeballing a truck’s tires, you have hints of why tread looks like it does.
If you want the complete scoop, contact the Technology & Maintenance Council in Arlington, Va. (703-838-1763 or email
firstname.lastname@example.org) and get a copy of the Radial Tire Conditions Analysis Guide, which includes Recommended Practice 219D and other related documents. The guide costs $79 for TMC members and $105 for nonmembers.
By the way, TMC would welcome you as an owner-operator member. Check into that, too. LL