Value & Pitfalls Of Low Trailer Deck Height

To some people it matters, to others not so much. Yet you read about it in trailer descriptions and axle descriptions a lot. So, what are the trade-offs with a low trailer deck height?

First, Advantages of a Low Trailer Deck Height

Thinking of trailers in action, the big advantages of a low trailer deck height have to do with loading, unloading and CG (Center of Gravity). Here are some more.

The step up onto the trailer is less with a low deck height. That makes loading things — whether equipment with machinery, or smaller things with people — much easier.
The step down off the trailer is less. With equipment or with people, it makes unloading easier.
When driving something onto a trailer (riding lawn mower, go-cart, motorcycle, …), a lower deck means shorter ramps, a lower approach angle, or both. It is certainly easier and less likely to damage the items driving on.
Once the load is secure, the trailer center of gravity is lower — which improves towing stability and cornering.
For a loaded or enclosed trailer, if the deck starts closer to the ground, there is less height above — often meaning less frontal area beyond the tow vehicle, so less wind resistance. This helps stability as well as fuel economy.
For a tiny house trailer, a low trailer deck height means you can build more house within the legal limits of total height. That gives more vertical space inside.

This is not a definitive list. Other factors may be your prime movers in the case of how you use the trailer. All of these are nice advantages and good reasons for a low trailer deck height. But what about the other side of the coin?

And Some Disadvantages

With all the good reasons for a lower deck, what can possibly be a disadvantage?

The biggest disadvantage is low approach and exit angles which cause dragging on the ground. When the deck is low, it usually means the trailer frame is low — giving a smaller exit angle. Also, if the deck is low, the tongue (hitch) is usually low — giving a smaller approach angle. Here is a diagram with the angles (red lines).

What you don’t see is how these angles interact with the tow vehicle — for backing into a driveway, driving over a speed bump, or though a dip. I’ve seen a lot of trailers hit the ground either at the hitch or the frame back.
Ground clearance for handling obstacles when driving. Not so much on the highway, though that is sometimes a factor, but more when maneuvering the trailer. Things on the ground can hit the underside. This is especially true when maneuvering on uneven ground where the approach and exit angles also play a role.
Anytime you need to get under the trailer, a low deck makes it harder. If the spare tire is stored under, for example. If there are wiring issues or (for some types of trailers) plumbing issues.
Deck-Over style trailers have a full width deck, and by nature, they have higher decks. So, for a low deck you probably have to deal with wheel wells or a narrower trailer bed.
When designing a trailer for low trailer deck height, people often take shortcuts that compromise other areas. Things like choosing main beams that are on the edge of sufficient, or smaller tires that are on the edge of capacity. Shortcuts inevitably lead to problems later — sometimes really big problems.

Please remember the magnitude of each of these disadvantages changes with the customer uses and with how low and how long the trailer really is. The lower the trailer and the longer the trailer, the more likely these disadvantages will become problems.

How Low Is Right?

The right height for the bed is subjective and really depends on the trailer purpose. A car hauler, for instance benefits greatly from a low trailer deck height because it’s much better for driving the car on. On the other hand, when a farm trailer gets low, they often drag the ground when driving in and out of the field. That can tear up things under the trailer (like lights, wires, etc.).

In general, make the deck as high as practical. . . . What? . . . Shouldn’t that be: Make the deck as low as practical? Well . . . . As the deck gets lower, more of the disadvantages creep in. A good example is a utility trailer. They have lots of uses, but we also see a lot of scrapes on the ground when they are too low. I have a trailer that I must pull into and out of the driveway somewhat sideways because it’s long and low. Also at gas stations and store entrances.

Another Rule of Thumb: The longer the trailer, the higher it should be. Hopefully that’s pretty obvious, yet I see it with tiny homes. They can’t park where they want because it’s too low for the obstacles. For a one time placement like with a tiny house trailer, work can be done to get it there, but for other trailers in normal use, a little higher is better.

Maybe these ideas sound wrong to you? Perhaps you have some thoughts to add? Let us know in the comments.

How To Achieve A Low Trailer Deck

Factors that contribute to a low trailer deck height are many. Some are fundamental with the trailer frame design, others are components that can be swapped. Things like Spring Position are a good example. Either way, it’s often a balance of “how low” versus the conflicts with so many other demands.

Thinking especially about DIY homemade trailers, there are lots of ways to achieve a lower deck. Some are good tricks, others are more common sense. Please read “How To Make A Lower Trailer Deck” for the list.