Trailer Tires Design And Load

Whether you’re towing a boat or driving an RV, you need the proper tires to safely make the journey.

Trailer tires rated ST, meaning Special Trailer, are designed to carry heavier loads than passenger or light truck tires.

Trailer tires are also engineered to prevent fishtailing and to dissipate heat that builds under the pressure of significant weight.

Trailer tires are distinguished by a solid center rib. This center rib provides uninterrupted contact with the road, allowing greater stability for your trailer.

These tires also feature stiffer sidewalls, which up their carrying capacity and reduce sway. A higher grade of belts, wider belts and more plies further enhance capacity and guard against damage.

Load Range

A few different rules apply when it comes to trailer tires. Since they don’t have UTQG (Uniform Tire Quality Grade) ratings, instead, they’re branded with a load range on their sidewall — a letter mark that tells you the ply rating and the max inflation to inflate the tires.

  • B 4 ply rating 35 psi
  • C 6 ply rating 50 psi
  • D 8 ply rating 65 psi
  • E 10 ply rating 80 psi

A combination of this rating and your tire’s size determines how heavy of a load they’re rated for.

Trailer Tires Design And Load
Trailer Tires Are Designed To Carry Weight

For example, “B” load range tires size ST175/80R13 inflated to 30 psi can take on a maximum load of around 1,000 pounds, and “E” load-range tires size ST235/80R16 inflated to 80 psi can take on a maximum load of around 3,400 pounds.

Multiply that weight by the number of wheels on your vehicle for total load capacity.

Whether you’re outfitting a horse trailer, pop-up camper or RV — know the combined weight you’ll need your tires to support before you shop.

When to Replace Trailer Tires

Another important difference with trailer tires is that they’re made so well that the integrity of their internal construction tends to degrade long before their tread blocks wear down.

Also, trailer tires do not carry a tread life rating, so when determining whether it’s time to replace them, you can’t rely on the penny test.

The last four numbers of the DOT number is the manufactured date of the tire. For example, if the DOT number ends in 3018, it means the tires were manufactured in the 30th week of 2018.

The tire’s manufacturer is the best source to find the life expectancy of your trailer tires as this will vary from manufacturer to manufacturer.

Regular inspections of your trailer tires can also help you to determine their lifespan.

Caring for Trailer Tires

To get the best out of your trailer tires, make the time to maintain them properly.

Don’t park your trailer fully loaded. If you are able to, raise the trailer so the tires are in the air.

If that’s not an option, regularly move the trailer by a foot or two, to give the wheels a quarter or half revolution. This will help prevent flat spots from forming in the tires.

The sun can also cause the rubber compound of your tires to breakdown, so park your trailer inside a garage or under cover on flat pavement.

Keep them clean by removing solvents, such as oil or grease, which are known to damage rubber.

Trailer tires are designed differently than vehicle tires. Consider these basics before you purchase your next set of trailer tires, so you can better enjoy your adventures.