Measure it once when nothing is wrong
Trailer alignment is almost always done as a reaction: the tires wore out early, so something gets measured.
There is a better version, and it costs the same. Measure a trailer when it is working fine, write the figures down, and you have a baseline. Every later measurement is then a comparison rather than a judgment, and the question "has this changed?" has an answer.
Fleets do this routinely for engines and rarely for trailers, which is odd given that a trailer carries most of the weight in a combination and runs more tires than the tractor pulling it.
What the measurement covers
Axle alignment to the kingpin, axle-to-axle relationship on a tandem or tri-axle, and the suspension and mounting hardware holding it together.
Monroe also aligns tractors. Measuring the combination rather than one end of it is the only way to establish which is responsible when a unit tracks badly, and for a fleet with fixed pairings it is worth doing both at once.
The symptoms, when you do not have a baseline
The national trailer alignment page lists them, and every one of them is a lagging indicator. That is the argument for the baseline: a measurement answers the question now, while a symptom list only answers it once the tires have paid for the information.
Drivers are not a reliable source on this. A trailer out of line transmits almost nothing to the tractor, which is why the tires are the better witness.
What a correction protects
The tires, and the casings under them. A trailer position scrubbed away on one shoulder will not pass at the plant, so the loss is the tire and its retread value together.
Monroe carries trailer tires and every other Purcell category and collects casings for the plant in Portland, so the measurement, the tires and the retread program sit in one place.
About this store
The Monroe store runs seventeen services and is managed by JR Webster. Lacey and Renton also align trailers.
See the national trailer alignment page for all 36 locations.