Trailer tires age out, not wear out
Most trailers don't roll enough miles to wear tread — the rubber dies of age first. UV, ozone, and heat cycles break down the casing from the inside, and the industry guidance for ST (Special Trailer) tires is replacement at 5–7 years regardless of tread depth.
Find the birthday on the sidewall: the DOT code ends in four digits — week and year. "3521" means the 35th week of 2021. Check every tire including the spare (spares age too, often faster, baking on a rear bumper). Cracking between treads or in the sidewall, or any bulge, means it's done today.
Inflation: the number comes from the load, not the sidewall
The pressure molded on the sidewall is the maximum for the tire's maximum load — not automatically your number. The right pressure comes from the tire maker's load/inflation table matched to what your axles actually carry. Get the rig weighed loaded (a truck-stop scale works; per-wheel weighing is better), then set pressure to carry that weight with margin.
Underinflation is the #1 blowout cause: a low tire flexes, flex makes heat, and heat delaminates the casing. Check cold pressures before every travel day — and a tire pressure monitoring system (TPMS) that alarms on pressure and temperature is the single best safety upgrade a towable owner can buy, because it catches the slow leak before it becomes a shredded casing and a torn wheel-well.
The 65-mph rule and load margins
Most ST tires are speed-rated at 65 mph unless marked otherwise (some newer ones carry higher ratings — check the letter on yours). Towing at 75 on a 65-rated tire builds heat exactly like underinflation does, and heat is the enemy. Slow down; the fuel savings are a bonus.
On load: aim to run at no more than about 85–90% of the tires' combined rated capacity. If your loaded weight puts you at the limit, the next load range up (D to E, for example) buys real safety margin — matched to wheels rated for the higher pressure.
Wheel bearings: the annual hour that prevents fires
Trailer wheel bearings live on grease, and they're serviced on time, not symptoms — by the time you hear growling or feel heat, damage is done. The standard interval is a repack every 12 months or 10–12,000 miles, whichever comes first: hub off, old grease cleaned out, races inspected for pitting or bluing, bearings repacked by hand with a quality high-temp wheel-bearing grease, new seals, and the castle nut set to spec (snug while spinning, then backed to the first cotter-pin slot — never preloaded tight).
Grease-fitting axles let you push fresh grease through, but they don't replace inspection — pumping grease into a hub with a torn seal just pushes it onto your brakes. At every fuel stop, lay a hand near each hub: they should be warm, and all about the same. One hot hub is a bearing crying for help — deal with it before the next leg, because a seized bearing can drop a wheel or start a fire.
The pre-departure walkaround
- Cold tire pressures set to your load table numbers — every travel day, TPMS or gauge.
- Eyeball every sidewall for cracks and bulges; check tread for uneven wear (inner-edge wear on one side hints at a bent axle or worn suspension bushings).
- DOT date codes: anything past 5 years gets watched, past 7 gets replaced — spare included.
- Hand near every hub at fuel stops; investigate any one running hotter than its mates.
- Lug nuts torqued to spec and rechecked 50 miles after any wheel has been off.
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Frequently asked questions
How old is too old for RV trailer tires?
Replace ST trailer tires at 5–7 years old regardless of tread, spare included. Read the DOT date code on the sidewall — the final four digits are week and year of manufacture (e.g., 3521 = 35th week of 2021). Age, UV, and heat break down the casing long before the tread wears out on most trailers.
What causes most RV tire blowouts?
Heat — from underinflation, overloading, aged casings, or towing above the tire's speed rating (65 mph on most ST tires). Set cold pressure from the manufacturer's load/inflation table for your actual weighed load, keep total load under ~85–90% of tire capacity, and run a TPMS to catch slow leaks before they become blowouts.
How often should trailer wheel bearings be repacked?
Every 12 months or 10–12,000 miles, whichever comes first. Repack by hand with high-temp wheel-bearing grease, inspect races for pitting, fit new seals, and set the castle nut to just-snug before pinning. Feel each hub at fuel stops — one hub running hotter than the others is an early bearing failure warning.