Date codes, scale weights and a hand-packed bearing

The date code, and how to read it

On the sidewall, after the letters DOT, there is a string that ends in four digits. Those four digits are the week and the year the tire was manufactured. 3421 is the 34th week of 2021. The full code is molded onto one side of the tire only, so if you find a shortened version you are looking at the wrong face — go round and look at the inboard side with a flashlight.

Industry guidance, published by tire manufacturers themselves, is to replace RV tires on age regardless of tread — they and the NTSB put it at five to six years. The reason is that a trailer tire spends its life parked, loaded, in the sun. It fails from the inside out: the casing degrades where you cannot see it, and the tread you are looking at is measuring a wear process that mostly is not happening. Mileage is close to irrelevant. The date code is the number that matters.

Weigh it, do not guess it

Correct cold pressure comes from the actual weight on each axle, looked up in the tire manufacturer’s inflation table. The figure molded on the sidewall is the pressure for that tire’s maximum rated load, and your rig is almost certainly not carrying its maximum rated load. Over-inflated, a trailer skips over bumps and wears its tires down the middle. Under-inflated, the sidewall flexes, the tire runs hot, and heat is what kills RV tires.

So we set pressures from weight. It takes one trip to a scale, it is the single most-skipped step in this trade, and it changes the way a trailer tows more than any accessory you can bolt to it. It is also worth weighing corner by corner if you can, because rigs load unevenly — the kitchen side is usually heavier, and both tires on that axle get set for the heavier corner.

Bearings: annually, or every 12,000 miles

On a travel trailer this matters more than anything under the hood of a motorhome, and for a simple reason: there is nothing to warn you. No gauge, no light, no change in engine note. A dry bearing on a trailer axle announces itself by seizing, usually at speed, and by then the spindle is generally ruined too. That turns an hour on a bench into a recovery, a new hub and a machining job.

A proper repack means pulling the hub, cleaning the old grease out completely, inspecting the cone and the cup for pitting, scoring and brinelling — the little ladder of marks a loaded bearing leaves when it sits still for months — packing by hand so the grease is forced between every roller, fitting a new grease seal, and setting the preload properly. New seals every time. A seal costs a few dollars and is the only thing standing between your grease and your brake linings.

Why the grease zerk is not the same thing

Zerk-fitted axles are convenient and they have a place, but pumping grease in tells you nothing about what the races look like, and done carelessly it pushes grease straight past the inner seal onto the shoes. Contaminated linings do not clean up. If your axles have zerks and have never been opened, that is worth knowing about before a long trip rather than after one.

Brakes, measured

Electric trailer brakes wear at both ends: the shoes, and the magnets that get dragged across the drum face. Both get measured, not glanced at — lining thickness with a gauge, magnet face for uneven wear, the drum itself for scoring and for whether it has been machined past its limit. We also check that the magnets are actually drawing current, because a brake that is mechanically perfect and electrically dead is a brake that does nothing.

The re-torque nobody mentions

Lug nuts settle after a wheel has been off. They need re-torquing after the first fifty miles or so, to the figure for your wheels, in the right pattern. We write that figure on the sheet with the interval next to it. It is the most commonly skipped step after a wheel change and it is the reason wheels come off trailers.