Alignment & Wear
Evan Lockridge
Contributing Editor
One of the many things today's truck tires offer compared to those made not so long ago is extended tread life, thanks to improved rubber compounds. But to take full advantage of these improvements requires a different attitude when it comes to vehicle alignment.
Years ago, alignment meant simply a front-end job, but that's only the beginning of performing what's called total vehicle alignment, in other words, making sure all axles are tracking properly, including those on the trailer.
One of the best resources on total vehicle alignment is the Technology & Maintenance Council of the American Trucking Associations. Even if you have read its Recommended Practice called "Total Vehicle Alignment Recommendations for Maximizing Tire and Alignment-Related Component Life," first published a little more than five years ago, it may be time for a refresher, because it was revised about a year and a half ago. If you've never read it, then it's about time.
The first part of RP-642-A outlines recommended procedures for maximizing tread life, beginning when a truck is first put in service. It includes information on when to perform the first preventive maintenance inspection interval on the tires, as well as when to perform periodic maintenance later on and what to check any time a component is replaced that can affect the truck's alignment.
This RP also includes valuable information on what to look for when you visually inspect tires. According to TMC, tire wear is normally the best indicator of a vehicle's alignment condition. Tires that are wearing too quickly or irregularly are a good indication realignment may be needed.
For instance, there's information on what's called feather wear, one of the most common tire conditions that results from misalignment. This is when tread ribs or blocks are worn so that one side is higher than the other. On steer tires this can be a sign of toe condition. Toe is defined as the difference in distance apart – at the front and at the rear – of the steering axle tires as seen in a top view of the truck. Toe-in exists when the tires are closer together in the front than in the rear. Toe-out exists when the tires are closer together in the rear than in the front. If feather wear on both steer tires is in the same direction, drive axle or other chassis misalignment is indicated. However, if one steer tire shows feather wear and the other steer tire has normal wear, a combination of toe and drive axle or chassis misalignment is indicated.
In this RP you will also learn how seating a tire improperly on a wheel can result in irregular tire wear – typically seen as tread depth variations around a worn tire – and can lead to vehicle vibration as well.
Of course, as this RP points out, not all improper tire wear means your tractor-trailer is in need of a realignment. It may be a case of simply rotating tires. According to TMC, irregular or uneven tread wear patterns may be stopped or reversed by rotating a tire to another wheel position and possibly even reversing the direction of the rotation. This is particularly true of free-rolling wheel positions. "In fact, periodic rotation of steer tires can actually prevent, or at least delay, the onset of irregular tire wear," TMC says.
One of the biggest steps you can take in minimizing irregular tire wear due to alignment problems is finding a qualified technician who you can trust. The ultimate way to gauge the quality of a particular shop or technician is by tire wear performance, but that's something you can only judge long after someone has done work on your trucks. Fortunately the RP recommends steps you can take and questions you can ask to guide you in your decision-making process.
For more information on RP 642A, log on to ATA's web site at www.truckline.com and look for the TMC logo.
