Boat Trailer Tires and Maintenance

A very large number of anglers have boats on trailers. From lightweight aluminum rigs to very heavy fiberglass and Kevlar 20 plus feet boats, one thing all sizes of boats have in common is trailer tires. Boat trailer tires and maintenance of those tires is crucial to our bass fishing, we can’t get the boat to the lake without tires.

Boat Trailer Tires and Maintenance

Boat Trailer Tires and Maintenance – Radial or Bias Ply

Trailer tires are available in bias-ply or radial construction. However, radial tires are more popular in the larger sizes found on most bass boat trailers. By popular demand, the bias ply tire is pretty much limited to 8 and 10-inch tires. Bias ply tires are assembled with the plies running around the tread of the tire. Made with nylon and other fibers, they flex a bit and sometimes will form a flat spot from sitting for extended periods of time. Radial plies run across the tread from sidewall to sidewall. Radial tires designed for passenger car and light truck use, the sidewalls flex when making turns. Radial trailer tires flex as well but not as easily as their passenger counterpart. For this article, we will focus on radial trailer tires because they are more popular on larger bass boat trailers.

Boat Trailer Tires and Maintenance – Identification

Let’s start by discussing the numbers found on a tire. Tire companies went away from the letter tire size system used in the U.S. years ago and switched to the metric tire size system. Here is a typical boat trailer tire size and its breakdown.


ST – Special Trailer, used to be marked “For Trailer Use Only”

205 – Tread width in millimeters

75 – Aspect Ratio, sidewall height to tread width ratio

R – Indicates a radial tire. May also be a D for Diagonal or Bias-Ply

15 – Rim diameter in inches

Other information found on trailer tire sidewalls include:

Maximum Pressure – In many cases the suggested pressure. Some sources recommend reducing by 10% if traveling at speeds over 55 MPH

Load Range – Rating for how much weight the tire can support with its ply-rating

DOT date – Date of Manufacture

Boat Trailer Tires and Maintenance – Inflation is important

Most information on the tire’s side wall is self-explanatory. However, I’d like to touch on a tire’s “load range”. Load range rates how much weight the tire’s sidewalls can support. Generally, ST (special trailer) tires exceed LT (light truck) tires by 10% and P (passenger) tires by 40% in sidewall strength. So, while they look the same, trailer tires are quite different from light truck and passenger car tires. Always check the air pressure in trailer tires with a tire gauge, in many cases a radial trailer tire with low air will not bulge out like a passenger car radial tire. This is because the trailer tire has a higher sidewall load rating. If a trailer tire is visually low, do not drive on it, it likely has very little air in it.

Boat Trailer Tires and Maintenance – Killers

The three biggest enemies to trailer tires are under-inflation, overloading and oxidation from the sun. Under-inflation causes the tire to heat up at highway speeds thus weakening its internal parts. Overloading (i.e. load weight above the recommended range) stresses the tire because it’s not built to handle it. The sun causes oxidation to the outer layers of the tire. This oxidation causes those little cracks seen around the rim and tread. Those little cracks will grow into big cracks and are a sure sign of tire failure.

Boat Trailer Tires and Maintenance – When to Replace

Trailer tire manufacturers and the Rubber Manufacturers Association recommend replacing trailer tires every three to five years. Think about it, depending on where the boat is and an angler’s ability to use it, it may sit in the same spot for days, weeks or months with the elements doing their evil deeds to the tires. In these cases, the sun is baking the outer layers and a failure is likely. Depending on whether the trailer is a single or tandem axle the failure could be costly. For example, I have a 31.5-foot RV trailer I tow. One year while bringing it home from storage, on a local two-lane road, the front tandem tire failed. When it did, it took out the rear tandem tire, beat the wheel housing up and cut the electric brake wires. I know it isn’t a boat trailer, however the same kind of damage, or worse, can occur when a boat trailer tire comes apart at highway speeds.

Keep an eye on the condition of the boats trailer tires, monitor their pressures and keep them clean. Be careful with the products used to clean them, some cleaners can speed up the damage the sun does to tires. Check wheel bearings regularly, a damaged wheel bearing can immediately end a tires life. See “Hub Remove and Inspection” [see below] for the procedures to inspect wheel bearings. When hooking up the trailer for each outing it’s wise to verify the wheels’ lug nuts haven’t backed out. A quick visual inspection and rocking the trailer will identify loose lugs nuts. Every couple trips put a wrench on them and verify the torque. A loose tire will cause uneven wear and rapidly decrease a trailer tires life.

One final thought, don’t forget about the spare tire. A damaged or flat spare tire is useless on the side of the road. We have a lot riding on our trailer tires, take a few minutes on a regular basis and check those tires.

UB Garage Specialist

Cool Hub Removal and Inspection



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