The tire fails at 65 mph on I-69. The trailer starts moving sideways. You’re hauling a skid steer worth $45,000 on a five-figure equipment trailer, but none of that matters while you’re holding the steering wheel steady, easing off the accelerator, and trying to reach a safe shoulder without making an abrupt steering or braking input.
That situation happens more often than it should, and the tire does not have to be bald to fail. Trailer-tire failures can involve age, underinflation, overloading, excessive speed, road-hazard damage, uneven load distribution, worn suspension components, damaged wheels, failing valve stems, or a combination of those conditions. A tire can show plenty of tread and still have weather cracking, impact damage, or internal separation that cannot be seen during a casual walk-around.
Trailer tires also live a different life from most truck tires. Many trailers travel relatively few miles, then spend weeks or months parked outdoors while supporting a load. That means tread depth is only one part of the inspection. Tire age, cold inflation pressure, load capacity, speed rating, storage conditions, and the trailer’s mechanical condition all matter.
Age Matters More Than Tread on Trailer Tires
Passenger-car and work-truck tires often reach the end of their service life through mileage and tread wear. A lightly used utility, cargo, dump, or equipment trailer may age out before the tread wears out. It may travel only a few thousand miles per year while spending most of its time parked, exposed to sunlight, temperature swings, moisture, ozone, and a constant load at the same contact points.
Tire rubber naturally changes as it ages. Heat, oxygen, ozone, ultraviolet exposure, repeated flexing, improper inflation, and long-term storage can contribute to hardening, weather checking, cracking, and deterioration of internal components. Not every dangerous condition is visible from the outside. Impact damage and belt or ply separation can begin internally before a bulge, vibration, or obvious tread distortion appears.
There is no single federal rule requiring every trailer tire to be replaced at exactly five, six, or ten years. Tire and vehicle manufacturers publish different inspection and replacement guidance, and service conditions matter. For a working trailer stored outdoors and regularly operated under substantial load, inspecting the tires more aggressively after five years and planning replacement around the five-to-six-year mark is a sensible, conservative practice. A warranty period is not a guarantee that a tire remains safe for that entire period.
At Spencer Trailers, six years is a practical replacement point for most working trailer tires, especially when their storage history, inflation history, or previous loading is uncertain. Tires with cracking, bulges, repeated air loss, impact damage, excessive wear, or an unknown history should be removed sooner. Do not assume an older tire is safe simply because another manufacturer mentions a longer maximum age for a different tire type or application.
Before you judge the tread, check the tire’s manufacture date, the trailer certification label, the specified cold inflation pressure, the tire’s load and speed ratings, and the condition of the wheel and valve stem.
Reading the DOT Date Code
Highway tires manufactured since 2000 use a four-digit date code at the end of the complete DOT Tire Identification Number, commonly called the TIN. The first two digits identify the week of manufacture, and the final two identify the year.
For example: DOT XXXX XXXX 2319 means the tire was manufactured during the 23rd week of 2019. As of July 2026, that tire is a little more than seven years old. On a working trailer, especially one stored outdoors, it should be replaced rather than trusted for another highway season because the tread still looks usable.
The complete TIN is required on at least one sidewall. The opposite side may show only a partial code without the four-digit manufacture date. Depending on how the tire was mounted, the complete code may face the trailer frame or may be visible from the outside. Check both sidewalls. You may need to roll the trailer slightly, use a flashlight and inspection mirror, or safely raise and rotate the wheel according to the trailer manufacturer’s jacking instructions.
Check every tire individually, including the spare. Tires installed as a set can have different manufacture dates, and a replacement tire may be several years newer or older than the others. Record the complete date codes instead of assuming all four tires are the same age.
- 0 to 3 years old: Age alone is usually not a replacement reason, but inspect pressure and condition before every trip. Check for punctures, impact damage, uneven wear, valve leakage, and proper wheel clearance.
- 3 to 5 years old: Inspect more closely at the beginning of each hauling season and before long trips. Pay particular attention to sidewall checking, tread-groove cracks, pressure loss, vibration, and uneven wear.
- 5 to 6 years old: Schedule replacement before a demanding highway trip, especially if the trailer is stored outside, frequently loaded near its rated capacity, or has an uncertain maintenance history.
- 6+ years old: For most working utility, cargo, dump, and equipment trailers, replace the tires rather than relying on tread appearance alone. Continuing to use them should not be based on a visual driveway inspection.
What Dry Rot Looks Like and When It Means Replace Now
“Dry rot” is the common name people use for weather checking and ozone cracking. It may appear as fine surface lines on the sidewall, cracking around molded lettering, cracks between tread blocks, or a web-like pattern where the tire flexes near the wheel. More advanced deterioration can produce deep cracks, exposed cord, bulges, tread distortion, or chunks of rubber separating from the casing.
Not every faint surface line proves that the entire tire carcass has failed, but visible cracking should never be ignored. A qualified tire professional should inspect a tire with weather checking, particularly when the tire is several years old or has been operated underinflated. Deep cracks, exposed cord or fabric, bulges, blisters, tread separation, or cracking that opens when the sidewall flexes are remove-from-service conditions.
Age is only part of the decision. A newer tire may also need immediate replacement after a curb strike, pothole impact, prolonged underinflation, overload event, wheel damage, or contact with petroleum products. Internal damage is not always visible while the tire remains mounted, so a questionable tire may need to be removed from the wheel for a complete inspection.
Direct sunlight and heat accelerate weathering. Ozone from electric motors, generators, transformers, and welding equipment can also affect rubber during long-term storage. Keep the trailer away from fuel, oil, solvents, and chemicals that can attack the tire compound.
UV-resistant tire covers help when a trailer must remain outside, but they are not a substitute for inflation checks and inspection. For extended storage, park on a clean, firm surface, use a suitable barrier between the tire and contaminated or moisture-prone ground, maintain the manufacturer’s specified pressure, and follow the trailer and tire manufacturers’ guidance about supporting the trailer to reduce long-term tire loading. Repositioning the trailer can change the contact area, but it does not reverse age-related deterioration.
Load Range: The Spec Most People Ignore
A trailer tire’s load range is part of its load-carrying specification, but the letter by itself does not tell you exactly how many pounds the tire can carry. Capacity also depends on tire size, construction, inflation pressure, whether the tire is used in a single or dual configuration, and the manufacturer’s published load-and-inflation table.
The familiar “ply rating” is a strength classification carried over from older tire construction. A modern 10-ply-rated tire does not necessarily contain ten physical body plies. Always use the maximum load, maximum pressure, load index, speed symbol, and application information molded into the actual tire, together with the trailer certification label.
The figures below are representative examples, not universal capacities for every tire carrying the same load-range letter:
| Load Range | Equivalent Ply Rating | Representative ST Size and Capacity | Common Application |
|---|---|---|---|
| B | 4-ply rated | ST175/80D13: about 1,100 lbs at 35 PSI | Very light utility and small boat trailers |
| C | 6-ply rated | ST205/75R15: about 1,820 lbs at 50 PSI | Utility, enclosed cargo, and lighter tandem-axle trailers |
| D | 8-ply rated | ST205/75R15: about 2,150 lbs at 65 PSI | Heavier utility, cargo, and equipment applications |
| E | 10-ply rated | ST235/80R16: about 3,420 lbs at 80 PSI | Many heavy equipment, RV, and gooseneck applications |
| G | 14-ply rated | ST235/80R16 all-steel: up to about 4,080 lbs at 110 PSI | Heavy equipment and gooseneck trailers when specified by the manufacturer |
Those examples show why you cannot select a tire by the load-range letter alone. Two ST235/80R16 tires may have the same physical dimensions while carrying different load ranges, maximum pressures, internal constructions, and load capacities. The wheel and valve stem must also be rated for the required load and inflation pressure.
Do not simply divide the trailer’s GVWR by the number of tires and call the result your tire requirement. Start with the trailer’s certification label and its Gross Axle Weight Ratings. Confirm the original tire size, load range or load index, recommended cold inflation pressure, wheel rating, and number of tires. Then weigh the trailer as it is actually loaded. Axle weights and, where practical, individual wheel-position weights provide a more accurate picture than total trailer weight alone.
Tongue or gooseneck pin weight is carried partly by the tow vehicle, so the trailer’s GVWR is not automatically distributed equally across every tire. At the same time, cargo loaded off-center can overload one tire even when the total axle weight appears acceptable. A tire should have reserve capacity above its actual wheel-position load, and the combined tire capacity must satisfy the trailer manufacturer’s certified axle requirements.
For example, a current Diamond C LPX207 in a 22-foot configuration can use two 7,000-lb Lippert axles with 235/80R16 14-ply-rated radial tires. That tire package should be evaluated against the trailer’s certification label and axle ratings. A same-size tire with a lower load range and lower maximum pressure is not automatically an equivalent replacement just because it fits the wheel opening.
Installing higher-capacity tires does not increase the trailer’s GVWR, axle capacity, coupler rating, frame capacity, brake rating, wheel rating, or legal payload. The trailer remains limited by its lowest-rated structural or running-gear component and by the manufacturer’s certification.
Inflation pressure is equally important. Underinflation increases sidewall flex and heat buildup and reduces the amount of load the tire can safely support. Overinflation beyond the tire or wheel limit increases the risk of impact damage and is also unsafe. Check pressure cold, before the trailer has been driven more than a short distance, using an accurate gauge with enough range for the tire. Do not bleed pressure from a hot tire; the increase after driving is expected.
The number on the tire sidewall is the tire’s maximum permitted cold pressure, not automatically the correct pressure for every trailer. Use the cold inflation pressure shown on the trailer’s certification label or in the manufacturer’s documentation. Many ST trailer fitments do specify the tire’s maximum cold pressure, but that must be confirmed rather than assumed. Do not lower the pressure merely because today’s load is light unless the trailer and tire manufacturers provide an approved load-and-inflation procedure based on verified weights.
Check all road tires and the spare before every trip. Inspect valve stems and caps, and make sure the valve hardware is rated for the pressure being used. A 110-PSI 14-ply-rated assembly requires different attention than a 50-PSI light-utility tire.
ST vs LT Tires: Use the Right Type
ST means Special Trailer. These tires are designed for non-driven trailer-axle service and are commonly used on utility, cargo, equipment, boat, RV, and car-hauler trailers. Their construction, load tables, inflation requirements, and performance characteristics are intended for trailer use.
LT means Light Truck. An LT tire is not automatically unsafe on every trailer, because some trailer manufacturers specify LT, commercial all-position, or dedicated commercial trailer tires on certain heavy-duty applications. The important rule is to use the tire type, size, capacity, pressure, speed rating, and wheel combination approved by the trailer manufacturer.
Do not replace an OEM-specified ST tire with an LT or passenger tire based only on price, tread pattern, or outside diameter. A tire that fits the wheel can still have insufficient load capacity, an incompatible pressure requirement, the wrong rim-width specification, or inadequate clearance under load. Passenger-metric tires may also require a load-capacity reduction when used on a trailer and should not be substituted without written manufacturer approval.
Current heavy-duty trailers may use 14-ply-rated all-steel ST radials or 17.5-inch commercial tire-and-wheel packages rather than the lighter trailer tires common on older equipment. Follow the certification label for that specific trailer and configuration. Diamond C specifications can change by model, GVWR package, axle package, and wheel option, so use the VIN-specific label rather than copying the tire information from a similar-looking trailer on the lot.
Goodyear Endurance remains a current ST radial line, and manufacturers such as Carlisle and Hankook also offer trailer-specific products. Brand reputation matters, but it does not replace proper fitment. Check the DOT date before buying, verify the load and speed ratings, and make sure the dealer is supplying a tire that meets or exceeds the trailer manufacturer’s original requirements.
Modern ST speed ratings vary. Some are rated for 75, 81, or 87 mph, while other trailer tires and specialty applications have lower limits. Do not assume every ST tire is limited to 65 mph, and do not assume a higher speed symbol makes the entire trailer safe at that speed. Obey the lowest applicable limit among the tire, wheel, trailer, tow vehicle, hitch system, roadway, and operating conditions.
The Sun Factor in Indiana
Spencer is in Owen County, and southern Indiana summers bring strong sunlight, high humidity, hot pavement, and repeated temperature cycles. A trailer parked in an open lot receives direct UV exposure while the tires remain loaded in one position. Dark pavement and limited airflow can add heat around the tire and wheel assembly even when the trailer is not moving.
Heat generated during towing is an even greater concern. Underinflation, overloading, excessive speed, brake drag, failing bearings, and misalignment can build damaging heat inside a tire that already spent years exposed to outdoor weather. That is why a pre-trip pressure check must be done cold rather than after the tire has heated up on the highway.
If your trailer lives outside:
- Use properly fitted, UV-resistant tire covers during extended storage. Keep the covers ventilated and remove them for inspection instead of assuming the covered tires are protected indefinitely.
- Park in shade when practical and keep the tires away from oil, fuel, solvents, standing water, sharp gravel, welding equipment, generators, and other ozone or chemical sources.
- Use a clean barrier under the tires during long-term storage when the parking surface may hold moisture or contain petroleum residue. Follow the trailer manufacturer’s directions before placing the trailer on stands.
- Maintain the cold inflation pressure listed on the trailer placard and recheck it whenever seasonal temperatures change. A tire can lose pressure while sitting even when there is no visible puncture.
- Inspect all tires at the beginning of every hauling season, monthly during regular use, and before every trip. Include the inward-facing sidewalls and the spare.
- Record the manufacture date for each wheel position somewhere convenient, such as in the trailer’s maintenance log or inside the fender. Update the record whenever an individual tire is replaced.
Signs Your Trailer Tires Need to Go Now
Age and weather checking are not the only reasons to remove a trailer tire from service. Look for these conditions during every pre-trip inspection:
- Tread depth at or below 2/32 inch: Built-in wear bars or a tread-depth gauge provide the best check. The penny test can be used as a quick screen: insert a penny with Lincoln’s head down. If the top of his head remains visible, the tread is approximately 2/32 inch or less. Replace the tire. For wet-weather hauling, replacing before the absolute minimum provides more water-evacuation margin.
- Uneven or irregular wear: One-sided wear, center wear, shoulder wear, cupping, feathering, or localized flat spots can indicate incorrect pressure, overloading, a bent axle or spindle, loose or worn bearings, wheel imbalance, alignment problems, damaged suspension components, or unequal load distribution. Correct the cause before installing new tires.
- Bulges, blisters, or tread distortion: These can indicate broken cords, impact damage, or internal separation. Do not drive the trailer on the affected tire. Replace it or install a serviceable spare before moving the trailer on the highway.
- Visible cord, fabric, or steel: Exposed structural material anywhere in the tread, shoulder, or sidewall is a remove-from-service condition.
- Deep cracks or excessive weather checking: Cracks that expose internal material, open when the sidewall flexes, or extend deeply around the sidewall or tread grooves require replacement. Questionable surface checking should be inspected by a tire professional.
- Sidewall or shoulder punctures: Damage outside the repairable tread area should not be patched. A small puncture in the central tread area may be repairable only after the tire is removed from the wheel and inspected by a qualified technician under the tire manufacturer’s repair limits. A plug by itself is not a proper permanent repair.
- Repeated pressure loss: A tire that repeatedly needs air may have a puncture, damaged bead, cracked wheel, leaking valve, loose valve core, or internal damage. Find and correct the cause instead of topping it off before each trip.
- New vibration, thumping, or visible tread movement: Stop and inspect the tire and wheel assembly. A separated belt or distorted casing can fail even when the tread depth appears normal.
- Impact or overload history: A tire that hit a curb or pothole, ran significantly underinflated, carried an overloaded wheel position, or operated beside a failed tire may have hidden internal damage. Have it dismounted and inspected.
Also inspect the wheel, lug hardware, hub, and valve stem. A cracked or bent wheel, loose lug nuts, dragging brake, overheated hub, or failing bearing can damage a new tire quickly. Replacing rubber without correcting the mechanical problem only resets the clock on the next failure.
A Quick Q&A
Q: Can I just replace two tires on a tandem axle instead of all four?
A: Sometimes, but only after the other tires have been inspected and confirmed to be serviceable. The replacement tires should match the required size, type, construction, load capacity, pressure capability, and speed rating. Keep matching tires on the same axle, and do not mix radial and bias construction on one axle. Significant differences in overall diameter or tread depth can affect load sharing. If all four tires are the same age, have the same storage history, or show similar deterioration, replacing the full set is the safer decision. Check the spare at the same time.
Q: My tires have plenty of tread, but the date code says 2018. Do I really need to replace them?
A: Yes. In 2026, those tires are approximately eight years old. For a working trailer, that is beyond the conservative replacement interval we recommend, regardless of how much tread remains. Replace them before another highway haul and inspect the wheels, valve stems, bearings, brakes, and suspension while the tires are off.
Q: What tire pressure should I run?
A: Use the cold inflation pressure shown on the trailer’s certification label, tire placard, or manufacturer documentation. Do not automatically use the sidewall maximum unless it matches the trailer specification, and do not reduce pressure simply because the trailer is lightly loaded. Check the pressure before the trip, when the tires have been parked for at least several hours, and never bleed pressure from a hot tire.
Q: Can I upgrade to a higher load range?
A: A higher load range may be appropriate when the trailer manufacturer approves it and the tire fits the wheel and available clearance. The wheel, valve stem, hub, and other components must support the higher inflation pressure. The upgrade does not increase the trailer’s certified GVWR or payload, and a heavier tire may change ride and wear characteristics when used at an incorrect pressure.
Q: Is a trailer tire-pressure monitoring system worth it?
A: A properly installed trailer TPMS can warn you about pressure loss or unusual temperature changes while towing, which is valuable on long trips and heavy equipment trailers. It does not replace a cold-pressure check, visual inspection, scale verification, or routine maintenance. A tire can suffer impact or separation damage without first creating a warning that gives you time to react.
Before You Buy a Used Trailer
When shopping for a used trailer, tires should be one of the first inspection points. Do not judge them by shine, tread depth, or what the seller says about mileage. Read the complete DOT date code on every road tire and the spare. Confirm that all tires match the trailer’s certification label for size, construction, load capacity, pressure capability, and speed rating.
A used 7×16 enclosed cargo trailer can look nearly new while sitting on tires that are already near the end of their practical service life. It may also have mismatched replacements installed at different times. Check the inward-facing sidewalls, tread grooves, valve stems, wheels, and spare rather than inspecting only the side visible from the curb.
Build the cost of a complete matched set into your purchase math. Quality 15-inch trailer tires, mounting, proper valve stems, and disposal can total several hundred dollars. Heavy-duty 16-inch all-steel or 17.5-inch tire-and-wheel packages can reach or exceed four figures, depending on the required load range, wheel rating, brand, and installation. Obtain a current quote for the exact size instead of relying on a generic tire budget.
Look beyond the tires, too. Uneven wear may be evidence of a bent axle, worn suspension, loose bearings, incorrect alignment, overloaded service, or poor cargo distribution. Check the axle tags, brakes, hubs, spring hangers, equalizers, welds, coupler, safety chains, breakaway system, and certification label before deciding that four new tires are the only expense.
At Spencer Trailers, new trailers from our lineup, including Diamond C, Liberty, and Wells Cargo, are supplied with factory-specified tire-and-wheel packages selected for the trailer’s certified axle and placard requirements. The exact tire package can vary by model, GVWR, axle configuration, and optional equipment. We still recommend checking the DOT dates, cold pressure, lug torque, and visible condition when taking delivery and before every haul.
Buying new does not eliminate the owner’s maintenance responsibility. Tires can lose pressure while a trailer sits, and a new tire can still be damaged by a road hazard, overload, brake drag, or improper storage. Keep the certification label legible, maintain a written service record, and replace tires with specifications that meet the requirements for that exact trailer. Browse our current inventory if you’re at the point where the trailer itself needs replacing, not just the tires.
If you’re not sure what you’re looking at on your existing trailer, bring it by the lot at 291 West State Hwy 46 in Spencer. We can inspect the tire dates, ratings, pressure requirements, wheels, hubs, bearings, brakes, suspension, and visible wear patterns. Sometimes a properly matched set of tires is the right answer. Sometimes the wear is warning you about a larger running-gear problem, and sometimes replacing the trailer makes better financial sense. Either way, give us a call at (812) 829-0226 and we’ll help you figure it out before the highway does.
