Boat Trailer Tires

trailer tires
Special trailer tires (marked ST) have stiffer sidewalls and should be inflated to max pressure while carrying a load. They should never be used as passenger tires since they are not flexible enough.

Tire troubles are the number one reason for calls to BoatUS’s roadside assistance. When my buddy Lee asked me recently where he should get tires for his boat trailer, he was just considering one page of an encyclopedia of hard-earned trailer tire advice.

“Are you replacing them in pairs? How old are they? Are they dry-rotted?” went my barrage of questions. “They’re practically new,” Lee assured me, “from 2005 when I got the boat — I’ve only used the trailer a couple of times a year.”

Lee didn’t realize that eight-year-old tires are not new. I  told him that the average life of a trailer tire is  three to five years, even with very few miles on them. If the tires sit on the ground year-round and freeze in the mud over the winter, the sidewalls can break down, and they can also get flat spots from sitting. I gave him the following advice to preserve his tires in the future if his trailer isn’t in frequent use:

  • Jack or block up the trailer so the tires don’t sit on the ground.
  • Bleed a little air from the tires.
  • Cover the tires to prevent the sun from dry-rotting them.

Before you run out to buy new special trailer tires (marked ST) here are some things you should know.

Load Range

Make sure to get tires rated for the weight they are going to collectively carry. As an example, if you have a 5,000-pound boat and trailer package (GVWR) you’d want the tires to distribute this weight evenly, plus a 20-percent safety factor. So, each of my four tires should be rated for 1,500 pounds. Often, just replacing the original tires works, but to be sure, take a look at the tires’ sidewalls to identify the load range. ST metric-sized special trailer service tires will be branded with their load range on their sidewalls . See the accompanying picture to decipher the markings. In most cases it will be best to replace tires in pairs to ensure even wear and smooth running.

ST trailer markings
Trailer tires have their load range marked on the sidewall. Photo: Carlisle Transportation Products


To recap some of the main tips:

  • Buy the safe load range for your application.
  • Buy them in pairs for each axle.
  • Take the weight off them when not in use.
  • Cover them to prevent oxidation and dry rot.
  • Inflate to max pressure when in use. Under-inflated tires are the number one reason for failure.
  • Use a tire gauge to ensure max inflation; stiff sidewalls hide under-inflation.

Here are some other facts on trailer tires.

And here is more I’ve written about boat trailer maintenance.

Written by: Peter d'Anjou

A USCG licensed captain and former merchant mariner, Peter d'Anjou is now a freelance writer and editor. A one-time executive editor at Sailing World magazine, he writes about his passion for racing and boating. Having managed a large yacht repair facility in the NE U.S. his background in boat construction and repair translate to the practical side of boat ownership.