Value & Pitfalls Of Low Trailer Deck Height

To some people a low trailer deck height really matters, to others not so much.  Yet you read about it in trailer descriptions a lot.  So, what are the trade-offs for a low deck?  And how do you achieve it?  Is it even worth it?

If a low deck height is one of your trailer design goals, there are some great advantages, along with some drawbacks.  Hopefully this article will help with the balance to make your trailer awesome.

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.

1. The step up onto the trailer is less with a low deck height.  That makes loading things — whether equipment with machinery, or smaller things by hand — much easier.
2. The step down off the trailer is less.  With equipment or with people, it makes unloading and access easier.
3. 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.
4. Once the load is secure, the trailer center of gravity is lower, which improves towing stability and cornering.
5. 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.
6. 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 list is not definitive.  Other factors may be the prime movers in how you use the trailer.  All of these are nice advantages and good reasons for a low trailer deck height.  Now, 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?

1. The biggest disadvantage is the low approach and departure angles which cause dragging on the ground.  When the deck is low, the trailer frame is low, and the hitch is low — giving smaller approach and exit angles.   The angles illustrated in red in this diagram.
   
   What you don’t see is how they interact with the tow vehicle — for backing into a sloping driveway, driving over a speed bump, or though a dip.  I have seen a lot of trailers hit the ground either at the hitch or at the back.
2. Ground clearance for handling obstacles when driving.  Not so much on the highway, though that can happen, but more when maneuvering.  Things on the ground hit the underside.  This is especially true when maneuvering on uneven ground where the approach and exit angles also play a role.  Like and RV in a tight campground.
3. 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, plumbing issues (some trailers).
4. To achieve a low trailer deck height, some trailer features are not really possible, like Deck-Over style trailers where the deck is over the wheels.
5. When designing 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 small tires on the edge of capacity.  Shortcuts will inevitably lead to problems — sometimes really big problems.

Remember, the magnitude of each disadvantage changes with customer uses and with how low and how long the trailer is.  The lower the trailer, the longer the trailer, the more likely these disadvantages will be problems.

How Low Is Right?

The right height for a trailer bed is subjective and really depends on the purpose.  A car hauler, for instance benefits greatly from a low trailer deck height because it is 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? . . . Should not 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 I must pull in and out of the driveway at an angle because it is long and low.  Also at many gas stations and store entrances.

Another Rule of Thumb:  The longer the trailer, the higher it should be.  Hopefully that is pretty obvious, yet I see it with tiny homes.  They can’t park where they want because it is too low for the length and 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.

One Other Thought:  How do you tow your trailer?  Many low trailers suffer from pitch issues due to the hitch height, so the back end and the exit angle get dangerously close to things.  So, if you want a really low trailer, be prepared to do some attitude adjustments for towing.

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

Bandaids That Might Create Bigger Problems

There are a few “corrections” out there worth talking about.  First, one of the best ways to lower a trailer (if the trailer does not have it already) — change to drop axles.  While it sounds easy, using a drop axle can create some other issues.  (Same for changing to a different neutral angle on a torsion axle.)  Things like clearance at the fenders and clearance to other things.

Another way to achieve a low trailer deck height is using smaller wheels and tires.  It drops the deck, but may have a slightly harsher ride.

On the other hand, if your deck is too low, use either of these ideas, backward, to raise the trailer deck.  Larger tires, or straight axles.  These can make a pretty big difference in the approach and departure angles too.  Off-roading trailer often have bigger tires for this exact purpose.

Add skid plates or rollers to the rear of the trailer.  Now this is really a bandaid.  I think it is generally a great idea, if . . . . However, it actually adds material under the trailer, therefor making the actual departure angle less.  While it can protect the tail of the trailer, if you put too much weight on them, the whole trailer may bend (or fold or whatever you want to call it.)  I am not against skid plates or tail wheels, but do not put a lot of weight on them.

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 swap.  Things like Spring Position are a good example.  Either way, it is often a balance of “how low” versus the conflicts with so many other demands.

When considering the connection to the tow vehicle, the adjustable hitch or adjustable ball mount are often attractive.  Consider carefully the choices in context of the tow vehicle.  The wrong choice will make the ingress angle for the trailer much worse.  See these practical considerations for choosing the right adjustable ball mount.

Thinking especially about DIY homemade trailers, there are a lot 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.

Trailer Plans Options For A Low Trailer Deck Height

Most of the trailer plans we offer here in the Mechanical Elements Plans Store have axle options.  For most of our plans, you can build the trailers with a Straight Axle, or with a 4″ Drop Axle.  The difference in ground clearance is 4″ – which is also the difference for deck height.

Then with some of our plans, like the deck-over trailers, the deck height is more or less dictated by the wheel height, so straight axles are really the only choice.

Then, there are a few trailer plans where the whole design changes to accomodate the low trailer deck height.  That is the case with Drive-Over Fender Trailer designs.  In this case, the top of the Drive-Over fenders are set by the wheel size, but the deck height is not.  Since the Drive-Over fenders are not easy to change, we offer one version of the trailer for Straight Axles, and a second version with a low trailer deck height using 4″ Drop Axles.  This allows you as our customer to buy the plans you need for the deck height, ground clearance, and function you want.

Interestingly, for both of our Drive-Over Fender car haulers, the 10K version has a trailer deck height 2″ lower just because of the tire size difference.

Let us know if you need a more information.