The most challenging part of a successful radial tire program today is choosing the right tread type, size, profile, and construction for your vehicle and service conditions. But once you've selected the tires, it's essential to have guidelines for addressing problems as they occur. They should be communicated to service technicians, preferably in written form, and should be simple and easy to understand.
Often referred to as “fingertip diagnosis,” the following guidelines are helpful in analyzing tire wear patterns. The only requirements are the ability to feel, or “read,” directional scrub edges on the tire tread surface, as well as some basic understanding of how different vehicle configurations affect tire wear.
Steer axle tires should be read first, since they're most susceptible to side forces. In fact, steer tires can often tell us more about drive axle or frame-related alignment problems than can drive tires. Examine each steer tire by simply moving the outstretched palm of your hand laterally across the tread face while feeling for a sharp edge. Note the direction of this feather edging in relation to the driver's position in the vehicle (left or right).
If the sharp edges are going in opposite directions, toe setting is likely the dominant tire wear mechanism. If they're on the inside of the ribs on both steer tires, excessive toe-in is the culprit. If the edges are on the rib sides toward the outside of the vehicle, excessive toe-out is likely. Toe-in can lead to premature wear of the outside shoulder rib on both steer tires, while excessive toe-out will wear both inside tread ribs.
If the outstretched palm test shows the direction of feathering to be the same on both steer tires, the dominant wear mechanism is probably a chassis thrust angle resulting from a misaligned drive axle, worn or loose suspension components, or frame misalignment.
A condition called “toe-out on turns,” while rarely seen on current models, is common to some older long-wheelbase trucks and buses. It produces a tread feather condition identical to toe-out, even though the toe setting is within spec when checked with the wheels in the straight-ahead position.
Steering systems are designed to make the inside wheel turn at a sharper angle than the outside wheel when cornering, using geometry controlled by the shape of the right and left side steering arms. No shape is perfect for all turning conditions, and large differences in wheelbase require changes in optimum steering-arm shape. Service conditions involving frequent sharp turns and vehicles with modified wheelbase dimensions sometimes show this type of wear on steer tires. The best solution is to choose steer tires that have very high resistance to lateral scuff wear, even at the expense of some high-speed straight ahead wear resistance.
Drive axle tires rarely show enough lateral feather wear to detect it using the outstretched-palm test. But sometimes they do develop a feather edge that's detectable around the tread rather than across it. These sharp edges can be felt by running your palm around the tread in the direction of forward travel on drive tires, and opposite the direction of travel on free rolling tires.
A little is normal, especially in high torque applications and on single drive axle trucks. If these wear conditions are excessive, however, the solution for drive tires is to select a different tread pattern with more rigid tread blocks or fewer lateral tread bars, especially on the tread shoulders. For free rolling applications, tires with shallower tread depths and/or less aggressive continuous circumferential ribs will usually help.
