When to replace RV tires: The age rule that saves your trip

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. This is a federal requirement rather than a maker's convention: NHTSA's rule, 49 CFR 574.5, requires the code to be molded onto one sidewall, which is why a tire fitted with its whitewall out can hide the number that matters most. 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.

Six years in service, replace. That is Goodyear's own 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. If you cannot prove when a tire was first mounted, the bulletin says to use the DOT date of manufacture as the clock instead. It applies to the spare too, which sits mounted and aging exactly like the running tires. The bulletin is also plain that age is not predictable per tire: temperature, storage and load history all change how fast the rubber goes, which is why the date is the reliable measure and the tread is not.

If you cannot prove service history. The manufacture date becomes the clock, and the tire is replaced six years from it. Have a tire professional inspect the set annually while they are in service, looking for sidewall cracking, belt separation and rubber degradation.

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.

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 and a comparable LT tire do not carry the same weight, because the ST's sidewalls and belts are built for trailer duty. Your tire maker's load and inflation tables carry the figures. 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.

An ST trailer tire's load rating is calculated at a stated speed, and for most of the ST tires on the road that speed is 65 miles per hour. The capacity is only valid up to it, and pulling a loaded trailer faster than the tire's rating strains it beyond what it was built to carry.

But the ceiling is not universal, and it has moved. Newer ST tires carry a higher speed symbol: Goodyear says its current ST line carries an N rating, which is 87 miles per hour, and other makers offer L and M. So the answer for your RV is molded on your own tire rather than sitting in a rule of thumb. Find the speed symbol on the sidewall and treat it as the limit; if there is not one, or you cannot read it, treat 65 as the ceiling. Whatever the symbol says, run your tires at their cold pressure and confirm the 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.

Every tire has a maximum load molded on its sidewall, and the RV industry sets a floor under how much of it a trailer may use. The standard is a 10 percent reserve: the tires on an axle have to be rated to carry at least 110 percent of that axle's rating, which is the figure on the trailer's certification label rather than the weight you happen to be carrying on the day. Axles rated above 8,000 pounds are the one exception, where the same standard allows a 106 percent reserve. Federal law asks only that the tires meet the axle rating with no margin at all, so the reserve is the industry's own addition, and it exists because a tire loaded right up to its rating has nothing left for heat, hills, wind, or an uneven axle split.

That floor is the builder's guarantee, not a check you can run. It is measured against the certification label, so it tells you what the trailer was built with. Your own check is different, and it starts with a real weight: the loaded weight, axle by axle, from a certified scale, taken at the heaviest wheel position. Compare that figure against the tire's maximum load rating and keep a reserve on purpose, because a tire carrying its full rated load has no margin left; the fix at that point is a higher load range or less load, not a different driving style. Our RV towing weight calculator does that arithmetic on your own numbers.

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. If you have changed tire size, or you are running a different load range than the label was written for, Michelin publishes load and inflation tables that give the pressure for the weight each tire is actually carrying.

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 to 2 psi for every 10 degrees the temperature drops, which is the range the makers publish rather than one figure: Michelin and Ford put it at about 1 psi, Goodyear at 1 to 2. 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.

• 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.