About Boat Trailer Tires

About Boat Trailer Tires. How many times have you seen a boat trailer by the roadside with one wheel chocked up and the owner gone to get the tire repaired?

Boat trailers take some punishment with both salt and fresh water. The trailer chassis gets corroded, the trailer electrics get waterlogged and often short circuit, the wheel bearings get corroded and seize.

In many cases the boat trailer tires are not properly inflated, or in poor condition for highway driving. Also in many cases there is no spare tire in case of a tire failure. How prepared are you with your boat trailer tires? Selecting the right wheel and tire rim is essential to match the exact load requirements of your boat trailer


What type of tire construction? Is it Bias or a radial tire?

What tire size? This is the percentage of section height to section width or aspect ratio?

What is the rim size? Of course the diameter will have to match the selected tire.

What type of application? Is it Special Trailer (ST) type or a passenger vehicle type?

What is the tire load range? This is the load carrying capacity and the inflation pressure? Remember that load is trailer, boat, and everything in the boat for overall weight. The tire inflation pressure is an important factor in both handling and tire life. Maximum inflation pressure is shown on the tire side wall and should always be checked when the tire is cold.


This isn’t easy when there are three different size identification systems used on trailer tires.

The Numeric System - (4.80 X 8) is primarily used on small trailer tires. This indicates the tire section width (4.80") and the wheel rim diameter (8")

The Alpha Numeric System - (B78 X 13 C) is prevalent on trailer tire sizes of 13" to 15". This indicates the air chamber size (B); Aspect Ratio (78); wheel rim diameter (13") followed by the load range (C)

The Metric System - (ST205 75D 15) which is now being phased in by the many trailer tire manufacturers. This indicates the tire application type (ST-Special Trailer); section width (205mm); Aspect Ratio (75); construction type (D= bias ply) and the wheel rim diameter (15")


Special Trailer (ST) tires are constructed to provide improved high speed durability and bruise resistance when subjected to heavy loads. Te boat trailer tire construction is quite different from standard automotive tires. The trailer tire has the same load range (or ply) from bead to bead and are of bias ply construction. This provides a stiffer side wall which gives much safer towing as it helps to reduce trailer sway.

You should not use Passenger Car (P) or Light Truck (LT) tires on a boat trailer. This is because the construction, which is usually radial or bias belted, gives greater and more flexible side walls. This often leads to increased trailer sway and a loss of control. So many times I have followed trailers on the highway and seen this sway in action, it’s scary!


It is absolutely crucial that wheel mounting nuts or lug nuts on boat trailer wheels are tight and properly torque. Improper wheel nut torque is a major cause for loosening lug nuts in operation. Loose lug nuts can cause wheel separation with potentially serious safety consequences.

You should check the lug nut tightness regularly and in particular with a new boat trailer. Do it at start of the season and end of the season and absolutely before any major highway trip. To properly check wheel nut torque you need a torque wrench. If you find that wheel lug nut torque is not being maintained after 2 or 3 re-torque applications, this would indicate there is something wrong with the nut studs, wheels and/or hubs and should be looked at and corrected. More about boat trailer parts and also about Boat Trailer Tires