Trailer Works

By Pat Piper

Here's how to keep your rig in top shape.

Trailer GuideClick to Enlarge


Identified as GAWR (Gross Axle Weight Rating) and found on the trailer's VIN plate, usually located near the trailer tongue, this tells you the maximum weight all the axles on the trailer can safely carry. For example, if a single-axle trailer has a 3,500-pound GAWR, this means the trailer can carry no more than 3,500 pounds, including the weight of the boat and trailer, engine, and fuel. If a double-axle trailer has a pair of 3,500-pound axles, its GAWR is 7,000 pounds. Axles are available in many weight capacities. Your trailer has either leaf springs or torsion axles (see sidebar).

Bunks Or Rollers

Your trailer holds the boat with a series of rollers or with a number of long boards (bunks). Cypress is preferable to the usual pine because it is a sturdier wood. Bunks are found on almost all classic boat trailers so the weight of the hull is more evenly supported on the trailer. Be sure to inspect the carpeting covering the bunk for any signs of excessive wear and replace it, or your hull can become marked. Similarly, inspect roller assemblies to ensure they turn smoothly. Roller trailers are preferred for areas with a high tidal range but you’ll see both at any boat ramp.


Located on the trailer tongue, many actuators have a master cylinder that holds brake fluid. As the trailer pushes into the slowing tow vehicle, the mechanical actuator activates the brakes on the boat trailer. You need an actuator that is designed specifically for either disc or drum brakes. In another system, an electric-over-hydraulic actuator is wired into the tow vehicle braking system and will electrically activate the trailer brakes at the same time the tow vehicle brakes are applied.


Boat trailer lights are either incandescent bulbs (the standard that has been in use for years) or the increasingly common LED (light-emitting diode) lights that burn cooler and last longer. Take the time and have someone turn on the truck lights, apply the brakes, and left and right turn signals while you ensure that every light operates as it should.


Boat trailer tires have "ST" (special trailer) or the words "Trailer Use Only" on the sidewall. Trailer tires have stronger sidewalls than passenger car tires to handle heavier loads and have less flex for greater stability.

Boat trailer tires usually have a higher psi (pounds square inch) inflation than your car or tow vehicle. Correct psi is listed on the trailer tire sidewalls and many times you’ll also find it on the VIN (Vehicle Identification Number) plate on the boat trailer. Inflate when the tires are cold. Under inflation is the primary cause of boat trailer tire problems. (For more on trailer tires read The Lowdown on Tires)


Every state has different rules about trailer brakes, but 37 of them set the weight of the trailer and boat at 3,000 pounds before brakes are required.

Brakes are either drum, which until recently were the most common braking system, or disc, which have fewer moving parts. Drums need to be adjusted every 3,000-4,000 miles while disc brakes are self adjusting. Both systems should be flushed with freshwater after immersion in saltwater (see article How To Wash Your Trailer).


Boat trailer frames are made of steel, galvanized steel, or aluminum. Steel and galvanized steel are heavier than aluminum. Steel has to be painted to prevent rust but galvanized doesn't. Aluminum is more expensive but when tow capacity is a concern, a lighter aluminum trailer makes it possible to tow more weight. Aluminum is preferred for saltwater as it won't rust. 

— Published: Summer 2013

Under Suspension

Leaf Springs

Leaf Springs

Leaf springs have been around for a long time (Leonardo Da Vinci used the technology when he built a catapult). Today, thin varied lengths of steel are laid on top of each other (as few as one and as many as six) and are designed to bend when the trailer hits a bump so that the boat being carried remains stable. The plus of leaf springs is they are inexpensive to install while the negative is they will eventually rust, especially if the trailer is used in saltwater. Rust most often occurs in between the leaves.

Torsion axles

Torsion axles operate as a single unit at each end of a trailer axle and provide a smoother ride. They are more expensive.

Torsion Axles



  • On-the-road assistance for your trailer and vehicle
  • Only $38 Annually! ($24 Membership + $14 TRAILER ASSIST)