Read the real age: The DOT date code
Look on the sidewall for the letters DOT, then a longer string of characters. The last four digits are the date of manufacture, week first, then year. A code ending in 2619 means the 26th week of 2019, so the tire was made in the middle of that year. A code ending in 0924 means the 9th week of 2024, early in the year. That whole string is the Tire Identification Number, or TIN, and the last four digits are the only reliable age a tire has.
Check every tire, including the spare and both sides of the trailer. RV tires are often replaced one or two at a time, so the dates can differ wildly across the same set. A tire that looks new may have sat in a warehouse for two years before it ever went on the RV. That warehouse time counts. If the code has only three digits, the tire was made before the year 2000, and at that age you replace it, no question.
The RV tire replacement rule
Six years in service, replace. Six is the number Goodyear states, and it sits inside the wider range most guidance falls in: inspect at five years, replace by seven. Goodyear's rule, from its tire service bulletin: any tire in service six years or more should be replaced even if it appears serviceable and even if the tread is not worn. NHTSA references the same aging risk. It applies to the spare too, which sits mounted and aging exactly like the running tires.
Six years from the DOT date if you cannot prove service history. If you do not know when the tire was first mounted, the DOT manufacture date becomes the clock, and you replace at six years from that date. At five years from either, have a qualified tire technician inspect for sidewall cracking, belt separation, and rubber degradation, and plan the replacement.
Never buy used RV tires. The service, storage, and load history of a used tire is unknown, and a tire that was overheated once, run flat, or overloaded can fail regardless of how it looks.
ST vs LT tires: The kind of rubber matters
The letter in front of the size tells you what the tire is built for. ST stands for special trailer, and it is the tire the trailer's certification label will specify. LT stands for light truck, and it belongs on the tow vehicle, not typically on the trailer, unless the replacement math is done carefully.
ST tires carry more load for their size. For the same size and load range, an ST tire typically carries roughly 10 to 15 percent more weight than a comparable LT tire, because its sidewalls and belts are built for trailer duty. If the trailer's label calls for ST tires, that is not a suggestion. Swapping in LT or passenger tires because they were cheaper or more available can mean running a tire that is not rated for the load.
Never mix ST and LT tires on the same axle. Different constructions, different load behaviors, and the pair will not share the load the way matched tires do. Replace all the tires on an axle with the same type, and match the size and load range on the certification label, not just what is in stock.
The 65 mph ST tire speed limit
Here is the number almost no one knows until a tire fails: the load rating of an ST trailer tire is calculated assuming a maximum speed of 65 miles per hour. The tire's capacity is only valid up to that speed, and running a loaded trailer tire faster than its rating strains it beyond what it was designed to carry.
Some newer ST tires carry a speed symbol that implies a higher limit, letters like L for 75 or M for 81. Those symbols reflect a brief heat-resistance test, not a recommendation, and unless your tire explicitly carries one, treat 65 as the ceiling, not a suggestion. If you regularly tow at highway speed, run your tires at their cold pressure and confirm your RV is not overloaded, because heat, load, and speed multiply against each other. A correctly loaded and inflated RV is the foundation everything else stands on.
The 15 percent load safety margin
Every tire has a maximum load molded on its sidewall. The lasting rule from tire engineers is to keep 15 percent headroom between that rating and the weight the tire actually carries. Keeping 125 percent of the measured load is even better. A tire that exactly matches its load has no margin for heat, hills, wind, or an uneven axle split, and those are the conditions that turn a tired tire into a failed one.
This is where the weight calculator earns its keep. You cannot know your tire's margin without knowing your real loaded weight, axle by axle, from a certified scale. Run our RV towing weight calculator with your actual cargo, then compare the heaviest axle end to the tire's load rating. If the margin is skimping toward 10 percent or worse, the honest fix is higher-capacity tires, not hope.
Pressures: The certification label, not the sidewall maximum
The pressure number molded on the sidewall is the maximum the tire can hold, not the recommendation for your RV. The number you want is on the trailer's certification label, usually on the tongue or frame near the axle. That label lists the correct size, load range, and cold inflation for the trailer's axle ratings. Fill to that label pressure, checked cold before you have towed anywhere that day.
Underinflation is the fastest path to a blowout. A soft tire flexes harder and builds heat, and a trailer already runs stiffer and hotter than the tow vehicle tires. Heat is the enemy. Tires lose about 1 psi for every 10 degrees the temperature drops, so check cold pressure through the season, not just in spring. A tire pressure monitoring system, properly programmed to alarm early, will catch the slow leak and the run-low condition before the sidewall fails.
The visual checks before every trip
- Sidewall cracking. Small radial cracks along the sidewall, and check the inner face too, the sun reaches it differently and inner cracks are easy to miss.
- Bulges or blisters. A bubble in the sidewall is internal belt damage, and the tire can fail without warning.
- Dry rot or crazing. A spiderweb of fine cracks means the rubber compound is breaking down.
- Belt separation. A ripple or waviness in the tread area can mean the belts are separating internally, a replace-now signal.
- Match the set. Same type, same size, same load range on each axle, and the DOT dates reasonable together.
Why age beats tread for RVs
A passenger car wears its tread out in 40,000 to 60,000 miles long before rubber age becomes the risk. An RV often accumulates fewer miles than the rubber's useful life, so the tires age out first. UV light, heat cycling, and time harden the rubber compound and break down the internal structure, which is why the DOT date, not the tread depth, is the number that matters.
The check that gets skipped
The spare. It sits mounted for years, ages exactly like the running tires, and it is the first thing people trust in an emergency. Same DOT rule applies, date it and replace it on the same six-year clock, and keep it at the same cold pressure.
How do I read a DOT tire date code?
The last four digits after DOT are the week and year of manufacture, in that order: 2619 is the 26th week of 2019. If the code has only three digits, the tire was made before the year 2000, and at that age you replace it, no question.
Can an RV tire be too old even with perfect tread?
Yes, and this is the core of RV tire safety. Age degrades the rubber regardless of tread. The industry guidance, per NHTSA-adjacent aging research and Goodyear's bulletin, is replacement at six years in service or six years from the DOT date.
Can I use LT tires instead of ST tires on my trailer?
Only with careful math. For the same size and load range, ST tires carry roughly 10 to 15 percent more weight, and the trailer's certification label calls for the type it was built around. If you change to LT, the replacement must exceed the load capacity of the original at its inflation, and you must never mix ST and LT on the same axle.
Why is the speed rating of an ST tire only 65 mph?
The load capacity of ST trailer tires is calculated assuming 65 mph. Some carry a speed symbol that implies more, but that reflects a short heat test, not a recommendation. Running a loaded trailer tire faster than its rating strains it beyond its design, which is why 65 is treated as the ceiling unless the tire explicitly states otherwise.
Is over-inflating tires for long storage a good idea?
Some owners add about 10 psi for storage to reduce sidewall flat-spotting, then drop back to spec before driving. It is a storage-only practice, never drive on the over-pressured figure, and it is secondary to getting the weight off the tires or moving the RV periodically.