How To Make A Trailer Longer

Sometimes I wish my trailer was longer.  Is there an easy way to make a trailer longer?  Is that even possible?  And, what are the limits or problems with making it longer?

Let’s look at ways to do it.  And, as you might expect, let’s also discuss the advantages and cautions of  increasing length.

In this article we’ll talk about ways to make a trailer longer, because it’s not always as it seems.  The construction of your trailer can make it easier or harder than we show here — especially if you are converting a trailer.  We recommend you use the ideas here as suggestions, NOT as directions.

For additional, related ideas, we have 2 other articles on similar topics.  Check out this previous post about making a trailer wider as another option for carrying more.  Also, the post on increasing load capacity.

Looking At The Big Picture

Adding length can mean different things to different people.  If you need additional tongue length, that’s one thing, but if you need more bed length, that’s another.  For this discussion we’ll limit the scope to increasing trailer bed or deck length.  Extending the load area.

For most trailer frames, adding a little length is not a problem.  Add 6″ maybe a foot.  More than that, and you should consider starting with a different design.  Length is the biggest contributor in the need for strength of the main beams, so if you extend the length more than a little, you probably need bigger overall main beams. **

** Well, that is if the trailer is to maintain it’s same capacity.  If you are downgrading capacity while adding length, that’s a different story, but for the sake of this discussion, we’ll assume the same overall load capacity.

I would much rather that you start with a trailer design that is too large, then shorten it (or narrow it) rather than stretch it.  For example, if you need a 13′ trailer, it’s better to start with a 14′, then shorten it.  You may not have the option, but this is the better approach.

Where Do You Add Trailer Length?

Adding length to the trailer deck does not change the science of where the axle goes.  So, if you add length only in one direction, like to the rear, then you probably need to move the axle back as well.  Contrastingly, depending on available space, sometimes you can add a little length to the front, over the tongue.  Be careful that you don’t make the tongue too short, however, because the trailer may then interfere with the vehicle in a tight turn or when backing.

The big hiccup to make a trailer longer is the axle position.  It’s fairly easy to add material to the trailer frame, but you must either add to both front and back (proper ratios), or you must move the axle after adding material to the frame.  (Note, here’s how to make the axle position calculations for an existing trailer.)

Calculations:

A good general rule of thumb for adding bed length is do it in the same proportions as exist on the trailer.  For instance, let’s look at an example where the current bed length is 10′, and the axle is located 5’10” from the front of the bed.  Let’s say you want to extend the bed and add in 12″.

The current ratio for the axle position is:

(Bend length in front of the axle) divided by (Total bed length) =

5’10” / 10′ = convert to inches = 70″/120″ = 0.58333 = 58.3% in front of the axle.

So, if we want to add 12″ to the deck, we should add 58.3% (about) to the front, and 41.7% (about) behind the axle:

12″ * 0.58333 = 7″ to the front.  Then, 12″ – 7″ = 5″ to the back.

That keeps the axle in the same relative position to the trailer deck.  (See #1 below.)

A similar result, add 12″ to the rear, then move the axle back 7″.  (See #3 below.)

This example illustrates the thought process in where to add material.  As you consider how to add material with the descriptions below, also think about how adding material changes weight distribution over the axle, AND stress due to longer (more spread out) loading.

Ways To Make A Trailer Longer

Adding To Length And Width

Now we know where the length should be added, next we must plan on how to accomplish it.  Like making a trailer wider, there are multiple ways to increase length.

  1. Add Material.

    The first and easiest option is to add material to the front and back of the existing trailer.  The image here is the same one shown in the “Make a trailer wider” article, because it really shows both.  This one shows a wood addition on a metal frame, but metal is usually a better option.  The advantage is minimal tear-up of the existing trailer.  The big disadvantages include the added weight, and the reduction in tongue length.

    Note that stress in the beams over the axles increases as the trailer gets longer, so some attention to reinforcing those areas is appropriate.

  2. Cut the Trailer Frame and Insert Sections.

    Cutting the trailer in sections, then adding material to extend the front and back is the next way to make a trailer longer.  While this option has a lot of possibilities, take care in the way you cut the trailer frame.

    The main reason to cut the frame is preservation of items already on the front and back.  For instance, the tongue and all its complexities — or for the back, lights mounting, hinged tailgate, ramps or other features that you want to preserve.

    You can cut the trailer above the axle, then lengthen it by inserting material, then weld it all together again.  And, install new suspension mounting.  The advantage is a single cut.  The disadvantage is cutting and seaming in the high stress area.  This requires more reinforcement when welding the frame back together.  Because new weld areas are not as strong as the original, reinforcement is a must.  (Yes, a good weld is stronger than the parent material, but heat distress (just beyond the weld) is never as strong.  More info in our post on safety factors.)

    A much better location to cut the trailer is near the back end.  Typically this area has lower stresses, so cutting and welding new pieces is easier to maintain proper strength.

  3. Add Material Then Move The Axle.

    As mentioned above, one option to make a trailer longer is adding material where it is easiest (based on your trailer frame), then move the axle to accommodate it.  For example, cut the trailer frame near the back end, then insert material for length.  Next, move the axle back to compensate for the difference in added length.

    This method with the cut location near the back as in the illustration below, puts the new material in an area where stress is lower.  That is a big advantage for longevity and future use.  The two areas of highest stress are:  1, near the axle;  and 2, (typically) within a few feet of where the tongue leaves the main part of the frame.  Material insertion in high stress areas requires more reinforcement when putting it back together.  See #2 above.

    Option 3 For Lengthening A Trailer
    Cutting, elongating, then inserting material preserves the ends.  Brace to weld so the frame rails are straight.  This image does not show added reinforcement that should accompany inserted sections.  Overlap the sides of the joint with added material at least.

    Depending on your trailer specifics, this option might be the only real way.  Or, it might be the most convenient — even though moving the axle is a hassle.

  4. Combinations of the Lengthening Options Above.

    Often the best approach is a combination of the above methods.  For instance, adding material in the front over the tongue, (plus an extension of the tongue if needed).  Then, cutting the trailer near the rear to insert new material there.  The sky’s the limit for blending the approaches, so be creative.  In large measure, the structure of the existing frame will dictate which approach, or which combination of approaches is best.

    That said, the fewer cuts and welds, the easier the project, and likely, the better the project will turn out.  It’s easy to think about, but harder to actually make a trailer longer.

Other Considerations

As with most things DIY, there are always some other things to consider as you start a project.  As we make a trailer longer, we have to think about the other things that also must become longer.  Trailer sides (if it has them) must extend, the decking (probably best to just replace it all), as do the wires for lights and sometimes brake lines.  Often it’s just best to re-do the wiring so you don’t end up with a bunch of splices.  Same with brake lines.

Your specific circumstances may also have other considerations.  Just think about all the details as you make choices on how to proceed.

A note on Aluminum:  If your frame is aluminum, make sure you weld good supporting structure around any areas where you cut the frame to add material.  We mentioned above about heat stress tempering the material around a weld, and that’s double true for aluminum.  It can be done, take care in doing it right.

A Sanity Check Before You Start

The potential to make a trailer longer is not as straightforward as widening or strengthening.  Think through all the possibilities carefully before cutting your frame.  You don’t want to make it weaker in the process.

My Recommendation?  If you need to add more than a foot in length, sell the existing trailer then, go get or build a longer one.  Think about it.  The existing trailer is probably worth more before it’s cut or cobbled.  Then, the new one will likely perform better and be nicer to use than the potentially cobbled one.  That’s not always true, yet it’s worth thinking about.

Good luck with your trailer lengthening project.

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