Distance is what makes a small error expensive
A trailer out of line by a small amount is being dragged very slightly sideways. Over a few miles that is nothing. Over a long corridor run, repeated, it is a continuous tax on rubber and fuel that never stops being charged.
Which is why trailer alignment returns more on a long-haul operation than on a local one, even though the error itself is identical. The misalignment is the same; the number of miles it gets applied to is not.
The corollary is worth stating too. A trailer that spends its life on short local work can carry a modest error for years without it costing enough to notice. The same trailer moved onto long-haul duty starts costing real money immediately, and nothing about the trailer changed.
A trailer reassigned from local to long-distance work is therefore worth measuring. It was fine before because the mileage was hiding the fault.
What the tires show at this distance
On a long route the wear pattern develops cleanly, which makes it easier to read than on a trailer doing varied work.
Wear that is opposite side to side across an axle is the signature. The national trailer alignment page covers the rest of the signs.
Both ends
Heavy-duty truck alignment is at the same store, so a combination can be measured rather than one end of it, and a fleet running consistent routes can tell afterwards whether it worked.
About this store
The Fernley store carries trailer tires and every other Purcell category, and is managed by John Jangula.
See the national trailer alignment page for all 36 locations.