Carl’s Trailer Sales
Trailer tires often age out before they wear out. A stock trailer can sit for months, then take a loaded trip to the sale barn. The tread can still look deep when the sidewall has been baking in the sun. That is why “how many miles” is the wrong first question.
Storage changes the life of trailer tires, and miles are only part of the story. Trailer tires stored in the sun can crack in the sidewall. People call those cracks dry rot. A tire that sits can flat-spot. Check tire pressure when the rubber is cold, and match the load range printed on the sidewall to the placard on the trailer. The spare on a stored trailer ages on the same clock.
There is no federal rule that says every trailer tire must come off at one birthday. NHTSA tells you to stop using a tire that is worn, cut, cracked, bulged, or damaged by low pressure or too much weight. NHTSA says some vehicle and tire manufacturers recommend replacing tires that are 6 to 10 years old, even when the tread remains. Your tire maker and the placard on the trailer are the instructions that apply to your setup.
Start here
The short version
Date code
The last four digits of the DOT number are the week and year the tire was built.
No single age
NHTSA, Goodyear, and Bridgestone do not share one replacement birthday.
Tread and cracks
Worn tread, cuts, bulges, and dry rot can finish a tire before the miles do.
The spare
A spare ages in storage too. Check it with the rest.
Read the date code first
The age starts with the DOT Tire Identification Number on the sidewall. It begins with the letters DOT. The last four digits are the week and the year the tire was built. NHTSA’s example is 0308, which means the third week of 2008. A code ending in 0921 means the ninth week of 2021. Goodyear uses the same reading in its RV tire bulletin.
Look at both sidewalls. NHTSA says the full number may be on only one side. Write the four digits down before you decide the tire is “about five years old.” A tire can sit in a warehouse before it is mounted, so the build date is not the same thing as the day it was first put in service.
What the tire makers actually say
NHTSA
Replace for wear, damage, or underinflation and overload damage. Some manufacturers recommend replacement at 6 to 10 years regardless of tread.
Goodyear, RV tires
Recommends replacing RV tires that have been in service 6 years or more, when they still look fine. If you do not know the in-service date, use the DOT build date.
Bridgestone
Inspect after five years. Remove tires manufactured 10 years prior, including the spare. Many tires need to come off sooner for wear or damage.
Goodyear’s RV bulletin, published through NHTSA, is careful about this. It says calendar age alone cannot predict when an RV tire should be replaced, and that no single scientific timetable covers every tire. The 6-year in-service recommendation is Goodyear’s guidance for RV tires, including the spare. It is not a law that covers every utility trailer in the county. If your tires are a different brand, follow that brand.
Walk every trailer tire
Do not stop at the tire closest to the shop door. Trailer tires on the sunny side and trailer tires on the shady side can tell two different stories. Check each tire, then the spare.
On every tire, read the date code, look at the tread, and feel the sidewall. Trailer tires with deep tread can still show dry rot. Trailer tires with even wear can still be old. Write down what you see so a clean tire does not talk you out of looking at the next one.
Wheels matter with the tires. A bent wheel, a loose lug, or a tire that sits crooked on the axle is a reason to stop. Low tire pressure on one tire overloads the other tires on that axle. That is how a short trip turns into a blowout.
Replace trailer tires that fail the tread, the sidewall, or the age guidance from their maker. Replace them as a set when the tires are the same age and one of them is done. Mixing one new tire with three older tires on the same trailer makes the new tire do more than its share.
Stored trailer tires need the same walk. Tires stored outside crack sooner. Tires stored under a cover still age. Flat spotting shows up as a thump for the first miles after a trailer has been sitting. Tire covers slow the sun. They do not reset the date code.
Passenger vehicle tires are the wrong fix for a trailer axle. Trailer tires are built for a heavy load that sits, then rolls. Car tires are built for a car. If you are unsure which tires are on the trailer, read the sidewall and the placard before you buy the next set.
Tread, cracks, and load still come first
A young tire can be done. NHTSA’s reasons to stop using a tire include tread worn down to the penny test, cuts, cracks, bulges, and irregular wear from low pressure or overloading. Trailer tires see long sits and then a heavy load. Low pressure on a loaded trailer is a common way to ruin a tire that still shows a fresh date code.
Use the tire placard on the trailer for size and tire pressure, not the number printed as a maximum on the sidewall. Check tire pressure cold, before the highway miles. The spare tire ages even when it never rolls. NHTSA says spare tires are easy to forget for that reason. Uneven wear on the tires usually means tire pressure, load, or an axle issue, not a mystery.
Here is the short version of the tire life check. Read the age on the tires. Look for wear on the tires. Look for cracks on the tires. Compare the tires with the placard. Then decide if you replace the tires or send the trailer out. Good tread on old tires is not a free pass. Fresh tires with a cut still come off. The life of the tires is the shorter of age, wear, and damage.
Weight matters as much as age. If you are matching a trailer to a truck, the GVWR vs payload guide explains why the scale reading and the hitch share the load. Hitch style changes the truck setup, which is covered in the bumper pull vs gooseneck guide.
A simple way to decide
Read the DOT date on every tire, including the spare. Look for cracks, bulges, and uneven wear. Confirm the pressure and the load against the trailer placard. If the tires are in the 6 to 10 year window your manufacturer talks about, or if you cannot tell when they were mounted, have them inspected before the next loaded trip.
Come see it in person
Carl’s Trailer Sales can look at the tires with the rest of the trailer at 10958 US HWY 212, Belle Fourche, SD 57717. Service is listed at trailer service and repair. If you are shopping a different trailer, start with trailers for sale in Belle Fourche. Call (605) 892-4032.
When to replace the tires
Replace trailer tires for tread wear, for dry rot, or for a date code that has reached the window your tire maker publishes. One flat tire is a reason to inspect the other tires, not a reason to ignore them. A cut in the tire tread or the tire sidewalls means that tire is done.
Miles are a clue. Life is the combination of miles, storage, and load. Rubber that looks chalky has been in the sun. Tire covers help stored tires. They do not stop age. Load range on the sidewall has to match the placard. The wrong tires on a trailer axle are a towing problem and a safety problem.
How long do trailer tires last if you do the walk every season? Longer than tires you never look at. Tires last when pressure is right, the load is right, and you replace them before the sidewall gives up. A blowout on the highway is the expensive way to learn the date code.
Frequently asked questions
How do I tell how old a trailer tire is?
Find the DOT number on the sidewall. The last four digits are the week and year it was built. A code ending in 0921 was built in the ninth week of 2021. Check both sides. The full number may be on only one sidewall.
Do I have to replace trailer tires at six years?
Not by federal law. NHTSA says some manufacturers recommend replacement between 6 and 10 years. Goodyear’s RV guidance says to replace RV tires that have been in service 6 years or more. Bridgestone says to remove tires at 10 years and inspect them after five. Follow the maker of the tire on your trailer.
Can trailer tires with good tread still be unsafe?
Yes. Age, cracks, bulges, and damage from low pressure or too much weight can finish a tire before the tread is gone. NHTSA lists those as reasons to stop using a tire.
Does the spare tire count?
Yes. Spares age even when they are not used. NHTSA and Bridgestone both tell you to include the spare when you check age.
Can Carl’s check my trailer tires?
Yes. Bring the trailer to Carl’s Trailer Sales in Belle Fourche for service, or ask when you are looking at inventory. We can help you match the date codes to the load the trailer is rated to carry.