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Aligning Rigs

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Several months ago, a trucking industry friend asked me, “How often should I align my trucks?”

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This is a fair question, to be sure, similar to those asked when establishing proper oil change intervals or setting time and mileage limits for cooling system maintenance. Before giving him a simple time interval, though, it occurred to me that a number of fleets no longer bother trying to establish alignment intervals. Instead, many now pose several related questions that are likely to result in more productive, cost-effective answers.

Questions like: How does one establish that a truck is in need of revision to its alignment settings? What is the best way to measure alignment?

Perhaps the best way to answer these questions is by considering what exactly we are trying to accomplish with “proper” truck alignment. The two primary goals that normally surface are assuring optimum vehicle handling and minimizing premature tire wear.

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Handling and Stability

Questionable truck handling or stability conditions are typically found by careful review of driver write-ups and can usually be confirmed in a short test drive. Load, speed and road type should be documented in handling-related driver comments, as these variables can accentuate or mask the offending condition. This is often key in making an accurate diagnosis.

For instance, “road walk” (directional instability) and “wander” can often be traced to a toe-out condition on the steer axle. Consistent pull to one side is normally caused by a drive axle that is not positioned square to the chassis centerline.

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With the high-torque drivelines of today, drive axle alignment should ideally be checked under power to observe if the axle changes position relative to the chassis centerline compared to its at-rest position.

While this isn’t always practical and is at least a two-person job, the exercise often reveals significant alignment changes. Worn bushings in radius rods or other suspension brackets can make static alignment efforts fruitless until these repairs have been made.

Significant differences in left-to-right side steer axle camber can also cause a right- or left-side pull. The truck will pull to the side having the more positive (or less negative) camber.

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Caster does not normally affect vehicle handling, except for excessively high caster, which can cause hard (high effort) steering, or excessively low caster, which can cause slow steering-wheel return to straight ahead after turning. Steer axle toe setting within normal limits doesn’t affect handling, with the exception of toe-out noted above.

Tire Wear Relations

Premature tire wear, on the other hand, is nearly always related to excessive tire side scrub and most often appears as a steer tire symptom. Improper steer axle toe setting is the most frequent culprit, with toe-in wearing the outside shoulders and toe-out wearing the inside shoulders.

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If, however, fast wear is observed on a steer tire’s outside shoulders only (or inside shoulders only), a chassis thrust angle resulting from drive axle misalignment is the likely culprit. A careful and knowledgeable look at both steer tires will allow an accurate diagnosis of the offending alignment condition.

There is normally little or no need to perform a complete truck alignment procedure beyond the specific correction required, provided that a technician with proper training and experience in interpreting driver write-ups and “reading” steer tire condition takes charge.

Of course, before returning them to service, any trucks that have been repaired after significant chassis damage and/or replacement of suspension or steering linkage components should be checked for proper alignment.

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Methods Of Truck Alignment

It is also important to understand the several different approaches used by manufacturers of alignment equipment. There are at least three approaches to truck alignment and, while each can provide satisfactory results, most service providers find the best results by choosing one and accumulating experience on only that type of equipment.

The first approach is to align axles and other wheel-end components to the chassis centerline, established either physically or theoretically. A second, and newer, approach aligns all axle wheel-ends to one another, so that tire scrub is minimized, and straight-ahead travel is assured with a minimum of tire scrub. This requires fitting sensors to each axle-end and checking these points relative to one another. This free-body approach is favored by some for current-generation trucks.

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A third approach is the tried and true, but very labor intensive, procedure of physical measurements: plumb bob drops and frame-based cross measuring referenced to a documented level surface. Because of the training and experience required to assure accuracy, such methods are usually reserved for collision repair and truck chassis modification experts.

Most experienced fleet operators agree it is wise to choose one approach to alignment checking/setting and to establish a data-based reference that relates known settings to truck handling and tire wear issues.

One other important consideration is that changes in truck wheelbase, configuration (single vs. tandem drive, for example), suspension type, driveline torque levels, and other such variables can affect the relationship between measured alignment settings and their effect on truck handling and tire wear. Alignment equipment companies and tire company field engineers are valuable resources for technician training in diagnosing and correcting alignment-related issues.

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Commercial Dealer Challenges

It appears that a growing number of well-managed fleets are taking a more measured approach when answering the question: “How often should I align my trucks?” Rather than basing the frequency on an arbitrary fixed mileage or elapsed time interval, the answer is becoming: “whenever they need alignment, based on a schedule of knowledgeable observation and service record review.”

Taking that approach is more cost-effective, will please more drivers and will free up valuable resources for other tasks, a far better choice vs. routinely running a large number of trucks through the alignment process.

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With fleet customers investing alignment time, labor and parts into only those vehicles requiring attention, you, as a service provider, should ensure that your technicians are properly trained. And, they should be trained, not only in alignment procedures, but also in the skills of relating tire wear and handling complaints to the specific variables needing attention.

The earlier these cause-and-effect detections can be accomplished, the greater value and cost savings you will be delivering to your fleet customer. This should also enhance your credibility and long-term customer relationships.

And don’t fret. Any diminished volume of traditionally scheduled alignment work should be more than offset with added alignment work resulting from a growing reputation as a true “expert” in this often complex segment of your servicing business.

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