Understanding Trailer Dynamics For That Long Haul

Trailer_DynamicsFor most of us, our trucks are frequently hooked to some sort of trailer. These trailers can range from a bumper-pull, single-axle boat trailer with two wheels to a 40-foot tandem-axle gooseneck trailer with eight tires (duals). Not only are there a wide range of trailers, but variations in how trailers are set up vary from manufacturer to manufacturer.

jon_5_BWWith all of the possible truck and trailer combinations out there, there is no way a single hitch or coupler height can work for everything. With this in mind, we decided to look into the importance of hitch height, and reached out to B&W Trailer Hitches to get an expert opinion on how best adjust the “in tow” height of a trailer.

“Towing a trailer that is level distributes the load better and it rides better,” says Beth Barlow, Market Manager for B&W Trailer Hitches. The load distribution between the axles on a tandem-axle trailer is extremely important for not only ride quality, but wear and tear, and even durability.

Towing a trailer that is level distributes the load better and it rides better – Beth Barlow, B&W Trailer Hitches

Before we even get into load distribution, we need to first examine why this is an issue.

The Issue

There are two distinct ways of mounting the springs to the axle of a trailer. In general, trailer manufacturers bolt the springs under the axle(s) of shorter trailers. This gives the trailer a lower deck height, making it easier to load and unload. For longer trailers, the springs are generally mounted to the top of the axle. This difference can change the deck height of the trailer two to four inches.



As the trailer angle increases, the rear axle is supporting a higher percentage of the weight. This increases the wear and tear on the axle bearings and springs, but it also wears the tires quicker, and generates more heat within the tires.

On the truck side of things, you have the difference between two- and four-wheel drive trucks (1.5 to 4 inches is common). “Over the years truck heights have come up and we are seeing more people towing with lifted trucks,” mentioned Barlow.

These are the most common reasons. There are other factors that can play into this such as tire size, bumper or receiver hitch, load leveling air bags, and even too much tongue weight (which is a common problem).

Free Body Diagram Example

The image above is a free body diagram of a basic tandem-axle flatbed car trailer. The basic principles in this example hold true for most any tandem-axle trailer, just the numbers and percentages change slightly. In our example, we are using a 20-foot tandem-axle trailer, which is actually about 24-feet long after you factor in the tongue length.

The arrows represent the loads.

Fl= The equivalent point force from the load on the trailer (i.e. center of gravity of the load)

Ft= The force of the ball

Fa1= The force on axle one

Fa2= The force from axle two

What Does This Mean

If we assume that the trailer plus vehicle (or load) has a combined weight of 10,000 pounds and the center of gravity is just far enough forward to result in a 10-percent tongue load (roughly 20 inches in front of the centerline of the two axles in this example), then we have an even weight distribution between the two axles on the trailer of 4,500 pounds with the trailer being level. If the trailer is at an angle of positive 10 degrees, the rear axle then is carrying 5 percent more weight than the front axle. If the axles are 5,000-pound axles, then the rear axle is at 95-percent capacity while the front axle is only at 88-percent capacity.

On short trips, the differences aren’t nearly as important as they are on long trips. On long trips, this extra weight can cause uneven tire wear, excessive heat, and additional fatigue which could lead to premature parts failure.

In addition to the fatigue and wear issues caused by an un-level trailer, the dynamics of the trailer handling can change. A trailer with more weight to the rear of the trailer has a greater likelihood of moving around on you (sway or fishtailing).

Assuming the tongue only has 10 percent of the load, this would be the weight distribution per axle with a 10,000-pound load and 20,000-pound load for a tandem-axle trailer (bumper pull, gooseneck and/or fifth wheel).

What Can Be Done

“You want to have some adjustability or multiple ball mounts to accommodate different trailers and truck heights. Two of our popular products that address this are the Tow & Stow adjustable ball mount and our adjustable gooseneck couplers,” explained Barlow.

The Tow & Stow adjustable ball is a single hitch that offers solutions to most bumper pull issues. The Tow & Stow is available in a three- to nine-inch drop with the dual-ball and tri-ball combination. The unit is adjustable in one-inch increments, and is available in black or chrome. The ball options are 2 and 2-5/16, 1-7/8 and 2, or 1-7/8, 2 and 2-5/16 of an inch. These are by far the most common hitch ball sizes on the market today.

The tri-ball hitch has the three most common size balls on a single assembly. With the removal of the pin, the assembly rotates around. To adjust the height of the ball or to stow the ball out of the way, there are two pins mounted in the back. With these removed, the ball assembly slides freely. There are two pins that keep the ball assembly in a track, preventing it from falling off. These pins also make aligning the holes easy.

The Defender Gooseneck Coupler features the standard B&W Trailer Hitch coupler assembly at the bottom which accepts the standard 2-5/16 ball. The coupler tube has five pin holes to allow up to five inches of adjustment to fine tune the tongue height of a gooseneck trailer. “This is important to keep the neck lined up evenly with the ball,” Barlow point out.


What a lot of people don’t realize is that having a gooseneck not square on a ball limits the movement of the neck. The higher the angle of the trailer, the less movement the trailer can make. When entering parking lots, the trailer can actually get in a bind if the range of movement is limited.

Taking advantage of the ease of adjustability, flipping the hitch over, can increase the angle of the trailer to make loading easier. Once the load is secure, simply unhook the trailer, flip the hitch over and away you go.

Additional Features

In addition to the Tow & Stow hitch offering a a great amount of adjustability in hitch height, the assembly is designed to be conveniently stored. Instead of having to either remove the hitch or smack your shin on it every time you walk behind your truck, the Tow & Stow is designed to flip the ball assembly around to avoid hassle. This ensures the hitch is always in the truck and that you don’t injure every single kid walking too close to your truck.

Because of the ball assembly’s ability to pivot, it is also easy to mount the Tow & Stow upside down. This raises the hitch height, making loading and unloading of vehicles much easier for car trailers. Then after the vehicle is on, simply drop the ball down and away you go. With other drop hitches, you have to remove the ball and flip it over to take advantage of the “raised height.” The time and effort that operation takes negates the benefits. With the Tow & Stow, it only takes a matter of seconds to change everything around.

Final Thoughts

When it comes to hauling things around, it is an extremely big inconvenience if you break down. Sometimes it is just a matter of understanding what you are asking the trailer to do, and making the appropriate changes to allow it to function the best it can. By letting the trailer ride level, loads are distributed better and the trailer tows better.


Suprisingly enough, the receiver height for our 2004 4WD Ford and 2006 2WD Dodge were only about an inch different. If you aren't careful when you measure for a drop hitch, then you may end up too low. According to these three images, we need about three inches of drop, but when the trailer is loaded, both of the trucks squat a couple of inches. When all is said and done, most of the time we are only using about a one-inch drop to level the trailer out (before we inflate the air bags in the truck.)

Article Sources

About the author

Chad Westfall

With diesel running through his veins from childhood, Chad has more than a decade of experience in the automotive industry. From editorial work to wrenching, there isn’t much he hasn't conquered head-on. When he’s not writing and shooting trucks and tech, you’ll find him in the shop working on turning the ideas floating around in his head into reality.
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